EP4728323A1

EP4728323A1 - Glazing inspection

Info

Publication number: EP4728323A1
Application number: EP24733688.6A
Authority: EP
Inventors: Jonathan JAKES; Bartlomiej BIELECKI; Sebastian BROCH; Marco Ronci
Original assignee: Pilkington Group Ltd
Current assignee: Pilkington Group Ltd
Priority date: 2023-06-14
Filing date: 2024-06-13
Publication date: 2026-04-22
Also published as: CN121336136A; WO2024256822A1

Abstract

A method of inspecting a glazing is described. The glazing is configured for installing in a vehicle having a head up display projector with a first projection distance from an eye box position. The method of inspecting comprises positioning the glazing relative to a light source; directing light from the light source to illuminate a portion of the first head up display region to produce a first virtual image at a first image plane, the first image plane being a first distance from the eye box position; imaging the first virtual image at the first image plane with an imaging system to capture a first image; and using the first image to determine a first performance parameter of the glazing; wherein the first distance is different to the first projection distance. Apparatus for carrying out the method is also described.

Description

GLAZING INSPECTION

The present invention relates to a method of inspecting a glazing having at least one head up display region and to apparatus for inspecting a glazing having at least one head up display region.

Head up display (HUD) systems for vehicles are well known. Such HUD systems are typically equipped with a head up display projector in the vehicle for projecting light onto the vehicle windscreen, whereby light is reflected from the windscreen thereby producing a virtual image in the line of sight of the vehicle driver when viewed through the windscreen. The virtual image therefore appears in front of the vehicle driver, behind the windscreen, when viewed from an eye box position inside the vehicle, the eye box position being representative of the eye position of the vehicle driver.

Vehicle windscreens are known for use in a head up display system where the virtual image appears at a projection distance of about Im to 3m or less (i.e. about 2m) from the eye box position. Such a head up display system may be used for displaying basic information about the status of vehicle, such as the speed of the vehicle in simple alpha-numeric characters. In the art such head up display systems are often referred to as “conventional head up display system”, or a “conventional HUD”.

More recently, head up systems have been developed to project more detailed information to the driver in the form of “augmented reality”, where information may be overlaid on the real -world view. Typically, this type of augmented reality (or AR for short) head up display has a larger projection area on the windscreen than the conventional HUD systems previously described. Furthermore, the image appears much further behind the windscreen from the perspective of the vehicle driver, often having a projection distance of about 10m (compared to Im to 2m for a conventional HUD) from the eye box position.

A vehicle with a HUD system having a tilted or inclined image plane is described in WO2017/195026A2. In such a system, different portions of a route (i e. for a journey) may be displayed on a tilted or inclined image plane. For example, a first portion of the route may be projected at a first focal distance and a second portion of the route at a second focal distance greater than the first focal distance, and a third portion of the route at a third distance greater than the second focal distance . The focal distances associated with a graphical overlay of the route may continuously vary between the first portion and the third portion to provide a smooth continuum or graduation of focal distances associated with the route, comparable with the focal distances of the real -world objects that correspond to the route.

A similar system is described in WO2019/131296A1, see for example figure 1 thereof and the related description. A HUD device is mounted on a vehicle and displays an image as a virtual image on a virtual screen which is set in front of a windshield by projecting display light indicating the image to the windshield. The HUD device is provided with a display unit that emits the display light; and a control unit that controls the image displayed on the virtual surface by controlling an operation of the display unit. The virtual surface is set so as to incline forward with respect to the vertical direction of the vehicle.

In order to assess the performance of a windscreen used in a head up display system for a vehicle, the windscreen is typically inspected prior to being installed in the vehicle. Usually light in the form of a matrix pattern is projected onto the windscreen and the image at the eye box position (or several eye positions in the eye box) is compared against predetermined head up display performance parameters deemed to be acceptable. Parameters such as ghosting, rotation, linear distortion, magnification and aspect ratio may be determined.

In head up display systems where the virtual image is Im to 2m from the eye box position the optical arrangement required to make the inspection measurements is relatively simple because the virtual image is small with a low degree of curvature. However, for a head up display system where the virtual image is much further away from the eye box position (i.e. about 5m - 10m or more as may be the case for an AR HUD), other factors such as image size and curvature of the windscreen become more prominent due to the increased distances involved. Angular alignment of the optical elements of the inspection system is also more critical due to the increased distance to the virtual image.

US 11,340, 453B2 discusses how in augmented reality HUD systems, the more substantially expanded image size and image curvature can cause parts of the image to always be displayed out of focus because of the limited depth of focus of the camera unit used during inspection. Problems due to astigmatism are also discussed.

The present invention aims to provide at least an alternative method for inspecting a vehicle windscreen that has a head up display region, in particular a head up display region for an augmented reality head up display system

Accordingly, from a first aspect the present invention provides a method of inspecting a glazing, the glazing being configured for installing in a vehicle having a head up display projector such that in use, light from the head up display projector illuminates a first head up display region of the glazing to produce a first virtual image at a first projection distance from an eye box position, the method of inspecting the glazing comprising: (i) positioning the glazing relative to a light source; (ii) directing light from the light source to illuminate at least a portion of the first head up display region of the glazing to produce a first virtual image at a first image plane, the first image plane being a first distance from the eye box position; (iii) imaging the first virtual image at the first image plane with an imaging system to capture a first image; and (iv) using the first image of the first virtual image at the first image plane to determine at least a first performance parameter of the first head up display region of the glazing; wherein the first distance is different to the first projection distance. By making measurements of the virtual image at the first image plane which is at the first distance from the eye box position, wherein the first distance is different from the first projection distance of the first head up display region when the glazing is installed in a vehicle, the present inventors have found it is possible to accurately assess the performance of the glazing at the first projection distance.

When the portion of the first head up display region is illuminated during (ii), the first virtual image is produced at the first image plane which is a first distance from the eye box position, and not at the first projection distance from the eye box position. This allows inspection measurements to be made only at the first image plane to determine performance parameters for different regions of the windscreen where such regions may be head up display regions having different projection distances when installed in a vehicle. Whilst the performance parameters measured at the first distance are not necessarily the same as the performance parameters measured at the first projection distance, the present inventors have surprisingly found that there is a good correlation between measurements of performance parameters made at the first distance with measurement of the performance parameters made at the first projection distance.

Preferably the first performance parameter determined at (iv) is compared with an appropriate performance specification. The appropriate performance specification is preferably a range for the first performance parameter at the first distance. For example, if the performance parameter value at (iv) is determined to be Pl, the performance specification may specify that /V can vary between Pl - pl and Pl + Ap2 Such a performance specification may be different for glazings intended for different vehicles.

Preferably the first performance parameter of the first head up display region of the glazing relates to ghosting, distortion, magnification, aspect ratio or displacement.

Preferably the first projection distance is greater than 3m, more preferably greater than 5m, even more preferably greater than 7m.

Preferably the first projection distance is less than 150m, more preferably less than 50m, even more preferably less than 20m, even more preferably less than 15m.

Preferably the first distance is less than or equal to about 4m.

Preferably the first distance is less than or equal to about 3m.

Preferably the first distance is less than or equal to about 2.5m.

Preferably the first distance is greater than about 0.5m, more preferably greater than about Im.

Preferably the first projection distance is between 7m and 150m, and the first distance is between Im and 30m with the proviso that the first distance is less than the first projection distance. Preferably the first projection distance is between 7m and 15m, and the first distance is between Im and 3m.

Preferably the first head up display region is for an augmented reality head up display system.

Preferably the first head up display region is about at least 5% of an area of the glazing.

Preferably first head up display region is less than about 50% of an area of the glazing, more preferably less than about 25% of an area of the glazing.

Preferably the glazing is a windscreen.

Preferably the glazing is a windscreen for a motor vehicle, a train, an aeroplane or a vehicle for use on water.

Preferably the glazing comprises a first pane of glazing material joined to a second pane of glazing material by an interlayer structure comprising at least one sheet of adhesive interlayer material, the second pane of glazing material being an inner sheet for facing the interior of the vehicle when the glazing is installed in the vehicle and the first pane of glazing material being an outer sheet for facing the external environment of when the glazing is installed in the vehicle; wherein the inner sheet has a major surface facing the interior of the vehicle when the glazing is installed in the vehicle and wherein the outer sheet has outer surface for facing the external environment of the vehicle in which the glazing is installed.

Preferably the imaging system comprises at least one camera.

Preferably the imaging system comprises at least one fixed camera for capturing an image of the first virtual image from a respective fixed eye position in the eye box.

Preferably the imaging system comprises at least one movable camera for capturing an image of the first virtual image from a first eye position in the eye box, the movable camera being movable to a second eye position in the eye box to capture a different image of the first virtual image.

Preferably the first image of the first virtual image is captured with a camera being positioned at the eye box position.

Preferably the first image of the first virtual image is captured with a camera being positioned at a first eye position in the eye box.

Preferably the eye box position has more than one eye position associated therewith.

Preferably the light source comprises a display.

Preferably the light source comprises a pattern of perforations backlit by a flat light source. Preferably the first virtual image at the first distance is configured to be parallel to the first virtual image at the first projection distance of the head up display system

Preferably the first virtual image at the first distance is configured to be parallel to the eye box position.

In some embodiments the first virtual image at the first projection distance is part of an inclined virtual image wherein the inclined virtual image is inclined relative to the eye box position. A vehicle having such a HUD system is described in WO2019/131296A 1 wherein the virtual image is displayed on a virtual surface set so as to incline forward with respect to the vertical direction of the vehicle

Preferably the first virtual image at the first projection distance is part of an inclined virtual image set so as to incline forward with respect to a vertical direction of the vehicle i.e. in a direction of forward travel of the vehicle.

In some embodiments the first distance is less than the first projection distance.

Preferably the first projection distance is greater than x m, wherein x = 3, or 4, or 5, or 6, or 7, or 8, or 9, or 10, or 15, or 20, or 30, or 40, or 50, or 60, or 70, or 80, or 90, or 100.

Preferably the first projection distance is less than y m, wherein y = 110, or 100, or 90, or 80, or 70, or 60, or 50, or 40, or 30.

Preferably the first projection distance is between 5m and 15m.

Preferably the first distance is not greater than j m, wherein j ' = 5, or 4.5, or 4, or 3.5, or 3, or 2.5, or 2, or 1.5, or 1, or 0.5.

Preferably the first distance is at least km, wherein k = 0.1, or 0.2, or 0.3, or 0.4, or 0.5, or 0.6, or 0.7, or 0.8, or 0.9, or 1, or 1.1, 1.2, or 1.3, or 1.4, or 1.5, or 1.6, or 1.7, or 1.8, or 1.9, or 2.

Preferably the first distance is between 0.5m and 5m, more preferably between 0.5m and 4m, even more preferably between 0.5m and 3m.

In some embodiments the first distance is greater than the first projection distance.

Preferably the first distance is greater than x ’ m, wherein x ’ = 3, or 4, or 5, or, 6. or 7, or 8, or 9, or 10, or 15, or 20, or 30, or 40, or 50, or 60, or 70, or 80, or 90, or 100.

Preferably the first distance is less than y ’ m, wherein y ’ = 110, or 100, or 90, or 80, or 70, or 60, or 50, or 40, or 30.

Preferably the first distance is between 5m and 15m. Preferably the first projection distance is less than or equal to j ’ m, wherein j ’ = 5, or 4.5, or 4, or 3.5, or 3, or 2.5, or 2, or 1.5, or 1, or 0.5.

Preferably the first projection distance is at least k' m, wherein k’ = 0.1, or 0.2, or 0.3, or 0.4, or 0.5, or 0.6, or 0.7, or 0.8, or 0.9, or 1, or 1.1, 1.2, or 1.3, or 1.4, or 1.5, or 1.6, or 1.7, or 1.8, or 1.9, or 2.

Preferably the first projection distance is between 0.5m and 5m, more preferably between 0.5m and 4m, even more preferably between 0.5m and 3m.

In some embodiments the first projection distance is greater than 20m,

Preferably the first projection distance is greater than x ” m, wherein x” = 30, or 40, or 50, or 60, or 70, or 80, or 90, or 100.

Preferably the first projection distance is less than y ” m, wherein y ” = 110, or 100, or 90, or 80, or 70, or 60, or 50, or 40, or 30.

In some embodiments the first image of the first virtual image is captured with the imaging system being positioned at the eye box position.

In some embodiments the first image of the first virtual image is captured at a first eye position in the eye box.

Preferably the method comprises capturing a second image of the first virtual image at the first image plane at a second eye position in the eye box and determining a first performance factor using the second image of the first virtual image.

In some embodiments a plurality of images of the first virtual image are captured, each image being captured at a different eye position in the eye box.

Preferably each image in the plurality of images is used to determine a respective first performance parameter.

Preferably each image is used to construct an image of the first virtual image, and the constructed image of the first virtual image is used to determine a first performance parameter.

In some embodiments the glazing comprises a first pane of glazing material joined to a second pane of glazing material by an interlayer structure comprising at least one sheet of adhesive interlayer material, the second pane of glazing material being an inner sheet for facing the interior of the vehicle when the glazing is installed in the vehicle, the inner sheet having an inner surface facing the interior of the vehicle when the glazing is installed in the vehicle, wherein the first virtual image that is produced comprises light from at least reflection from the inner surface of the inner sheet.

In these embodiments, the first pane of glazing material is an outer sheet for facing the external environment of the vehicle in which the glazing is installed, wherein the outer sheet has an outer surface for facing the external environment of the vehicle in which the glazing is installed.

Preferably the first virtual image that is produced comprises light from at least reflection from the interlayer structure.

Preferably the first virtual image that is produced in these embodiments comprises light from at least reflection from the outer surface. Reflection of light from the inner and outer surfaces may be used to determine a performance parameter related to ghosting.

In some embodiments the imaging system comprises a first camera at a first eye position in the eye box to capture the first image of the first virtual image and a second camera at a second eye position in the eye box to capture a second image of the first virtual image.

In some embodiments the imaging system is movable relative to the glazing to capture the first image with the imaging system at a first position relative to the glazing and to capture a second image with the imaging system at a second position relative to the glazing. The imaging system may be movable using a robot arm or the like.

When the imaging system is at the first position relative to the glazing, preferably the first image is captured at a first eye position in the eye box.

When the imaging system is movable and moved to the second position relative to the glazing, preferably the second image is captured at a second position in the eye box.

In embodiments when the imaging system is movable relative to the glazing, preferably a plurality of images may be captured to construct an image of the entire first virtual image.

In some embodiments light from the light source is in the form of a pattern, preferably comprising at least one dot and/or at least one line.

Preferably the pattern is specific for inspecting a glazing intended for a particular model of vehicle.

In some embodiments light from the light source is in the form of a pattern and the first virtual image of the pattern at the first image plane is distorted by the glazing, wherein the first virtual image distorted by the glazing is compared against a reference image of the pattern or a reference pattern when determining the performance parameter of the glazing.

As is known in the art, the reference image or reference pattern may be an undistorted image which is then distorted for projection onto the glazing being inspected.

In some embodiments the first performance parameter of the first head up display region of the glazing is determined using only the first image of the first virtual image.

In such embodiments, the first image of the first virtual image is preferably captured with the imaging system being positioned at a first eye position in the eye box

In some embodiments, during (li) light from the light source illuminates at least the entire first head up display region.

Preferably at (iii) the entire first virtual image from the entirely illuminated first head up display region is imaged and the captured first image is an image of the entire first virtual image.

Preferably only a portion of the entire virtual image from the entirely illuminated first head up display region is captured as the first image at (iii).

Preferably an image of the entire virtual image from the first head up display region is constructed from a plurality of images, each image in the plurality of images being of a different portion of the entire virtual image from the first head up display region. The plurality of images may be taken with the imaging system, which preferably comprises at least one camera which may be fixed or movable, at different eye positions in the eye box.

In some embodiments the performance the entire first head up display region is determined by carrying out steps (ii) and (iii) a plurality of times to illuminate a plurality of different portions of the first head up display region of the glazing.

Preferably each portion of the first head up display region is illuminated separately.

Preferably each different portion is used to determine a respective first performance parameter.

Preferably each respective first image from the different illuminated portions of the first head up display region is used to construct an image of the entire virtual image from the first head up display region. The image of the entire virtual image from the first head up display region so constructed may then be used to determine the first performance parameter of the first head up display region of the glazing

In some embodiments the glazing is configured for installing in the vehicle such that in use, light from the head up display projector illuminates a second head up display region of the glazing to produce a virtual image at a second projection distance from the eye box position, wherein the second projection distance is less than the first projection distance.

Preferably the method of inspecting the glazing comprises inspecting the second head up display region to determine at least a first performance parameter of the second head up display region of the glazing

Preferably method of inspecting the second head up display region comprises directing light from the light source or another light source to illuminate at least a portion of the second head up display region of the glazing to produce a second virtual image at a second image plane, the second image plane being at a second distance from the eye box position; imaging the second virtual image at the second image plane with an imaging system to capture a first image of the second virtual image; and using the first image of the second virtual image to determine at least a first performance parameter of the second head up display region of the glazing.

Preferably the first performance parameter of the second head up display region of the glazing is compared with an appropriate performance specification.

Preferably the second distance of the second image plane from the eye box position is the same as the first distance of the first image plane from the eye box position.

Preferably the second distance is the same as the second projection distance.

Preferably the first projection distance is between 5m and 20m and the second projection distance is between Im and 5m.

Preferably the first head up display region of the glazing has a first area and the second head up display region of the glazing has a second area, wherein the first area is greater than the second area.

Preferably the first area is at least 1.5 times the area of the second area, more preferably 2 times the area of the second area, even more preferably 3, or 4, or 5, or 6, or 7, or 8, or 9, or 10 times the area of the second area.

Preferably the first area is less than 20 times the area of the second area.

Preferably the first region is for an augmented reality head up display system and the second region is for a conventional head up display system.

In some embodiments the method is used to inspect a glazing that is configured for installing in the vehicle such that in use, light from the head up display projector illuminates a second head up display region of the glazing to produce a second virtual image at a second projection distance from the eye box position, wherein the second projection distance is greater than the first projection distance. Preferably the method of inspecting the glazing comprises inspecting the second head up display region to determine at least a first performance parameter of the second head up display region of the glazing

Preferably the second distance of the second image plane from the eye box position is the same as the first distance of the first image plane from the eye box position. This provides the advantage that measurements of the first parameter of the first and second head up display regions of the glazing can be made with the same optical arrangement, thereby speeding up the inspection procedure.

Preferably the first distance is the same as the second projection distance.

In some embodiments the method includes a calibration step such that during (iv), the first performance parameter measured at the first image plane can be transformed to a corresponding first performance parameter at the first projection distance or at another projection distance from the eye box position using at least a first correction factor determined during the calibration step.

Preferably the first correction factor is determined using ray tracing or measurement of the first performance parameter of a reference virtual image produced at the first image plane and the first projection distance or the another distance.

By determining an appropriate correction factor between the first performance parameter at different distances from the eye box position, such as at the first distance and the first projection distance, it is possible to make a measurement of the performance parameter at a first image plane being at a first distance from the eye box position and to calculate the performance parameter at the first portion distance. This may be useful if actual performance parameters at the first projection distance are required.

Preferably the first correction factor includes a factor for transforming at least one of ghosting, distortion, magnification, aspect ratio and displacement In some embodiments the head up display projector comprises at least a first projector for producing light to illuminate the first head up display region of the glazing.

In some embodiments, when the glazing is installed in a vehicle the eye box is at a standard location and may be movable to a higher location or a lower location depending upon a height of a driver of the vehicle.

In embodiments where the glazing has a first head up display region and a second head up display region, it is preferred that the head up display projector comprises a first projector for producing light to illuminate the first head up display region of the glazing and a second projector for producing light to illuminate the second head up display region of the glazing.

Preferably the first projector and the second projector are mounted in the same housing.

The present invention also provides from a second aspect an apparatus for inspecting a glazing, the glazing being configured for installing in a vehicle having a head up display projector such that in use, light from the head up display projector illuminates a first head up display region of the glazing to produce a first virtual image at a first projection distance from an eye box position; the apparatus comprising: a fixture, a light source, an imaging system and a computer; the fixture being arranged relative to the light source and configured to hold the windscreen during an inspection measurement such that light from the light source strikes the glazing to produce a virtual image at a first image plane, the first image plane being at a first distance from the eye box position; the imaging system being arranged relative to the glazing during the inspection step to capture an image of the virtual image at the first image plane through the glazing; and wherein the computer has a program for analysing the captured image of the virtual image at the first image plane to determine at least a first performance parameter of the glazing, wherein the first image plane is at a different position than the first projection distance.

Preferably the imaging system is positioned at the eye box position.

Embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings (not to scale), in which:

Figure 1 shows a schematic plan view of a vehicle windscreen having one head up display region;

Figure 2 shows a schematic side view representation of the vehicle windscreen of figure 1 installed in a vehicle;

Figure 3 shows a schematic side view of the apparatus carry out a method according to the first aspect of the present invention;

Figure 4 shows a comparison between a measured height of a virtual image element at the first image plane and at a second image plane different to the first image plane; Figure 5 shows the area of the windscreen illuminated with light compared to the area of the first head up display region; and

Figure 6 shows the area of six images captured to construct the entire virtual image due to the first head up display region being illuminated by a light source.

Figure 1 shows a plan view of a vehicle windscreen 1 configured with a first head up display region 3. In this example the first head up display region is for an augmented reality head up display system for a vehicle where a virtual image is produced about 10m behind the windscreen from the viewpoint of the driver of the vehicle.

In this example the first head up display region 3 is shown as being rectangular, but other shapes are possible, such as a trapezoidal perimeter.

Figure 2 illustrates a schematic side view of the windscreen 1 installed in a vehicle (not shown) at an installation angle 7 to the vertical. In use, a suitable head up display projector 9, which may include more than one projector system, illuminates the first head up display region 3. At the eye box position 11, when looking though the windscreen 1 the driver sees a first virtual image 15 at the first projection distance 19 from the eye box position 11. The first virtual image 15 at the first projection distance 19 from the eye box position 11 may be referred to as an in-use first virtual image, or an in-vehicle first virtual image.

As is known in the art, the eye box position may be movable upwards and downwards from a standard location to accommodate drivers having different heights, thereby ensuring a dnver’s eye is positioned in the eye box.

For an augmented reality head up display system the first projection distance 19 is usually more than about 5m, typically about 5m - 20m or about 7m - 15m, or about 8m - 12m i.e. about 10m.

The windscreen 1 is typically made from two glass sheets laminated together by an interlayer structure comprising at least one sheet of adhesive interlayer material such as polyvinyl butyral (PVB). The adhesive interlayer material for a windscreen having a head up display is usually wedged to reduce the occurrence of ghost images due to reflections from inner and outer surfaces of the windscreen.

As is conventional in the art, the glass sheets are typically about l-3mm thick and the PVB sheet is about 0.76mm thick. The glass may be soda-lime-silicate glass having a composition such as clear float glass, typically with the addition of iron oxide as a tinting agent to provide the laminated glazing with some form of solar control.

The overall thickness of the windscreen is typically less than 6mm. A typical soda-lime-silicate glass composition is (by weight), S1O2 69 - 74 %; AI2O3 0 - 3 %; Na₂O 10 - 16 %; K₂O 0 - 5 %; MgO 0 - 6 %; CaO 5 - 14 %; SO3 0 - 2 %; Fe₂O₃ 0.005 - 2 %. The glass composition may also contain other additives, for example, refining aids, which would normally be present in an amount of up to 2 %. The soda-lime-silicate glass composition may contain other colouring agents such as CO3O4 and Se to impart to the glass a desired colour when viewed in transmitted light. The transmitted glass colour may be measured in terms of a recognised standard such as BS EN410.

Other glass compositions are known in the art for use as an inner or outer sheet of a laminated glazing for a vehicle windscreen, such as aluminosilicate glasses. Such sheets of glass are typically used at a thickness less than 1mm, for example between 0.2mm and 0.9mm and may be chemically strengthened.

As is conventional in the art, the sheet of glass facing the external environment is usually referred to as the outer glass sheet and the sheet of glass facing the interior of the vehicle is usually referred to as the inner glass sheet. Each of the inner and outer glass sheets has a first major surface and a respective second opposing major surface, and when the windscreen is arranged such that the second major surface of the outer sheet of glass faces the first major surface of inner sheet of glass (the inner and outer sheets of glass being joined together with a sheet of PVB), the first major surface of the outer sheet of glass is usually referred to as “surface one”, the second major surface of the outer sheet of glass is referred to as “surface two”, the first major surface of the inner sheet of glass is referred to as “surface three” and the second major surface of the inner sheet of glass is referred to as “surface four”.

As is evident, “surface one” is the outer surface (or outer facing surface) of the windscreen 1 and “surface four” is the inner surface (or inner facing surface) of the windscreen.

Vehicle windscreens are also usually curved in one or more directions. The radius of curvature in one of the one or more directions may be between 1000mm and 8000mm.

When a vehicle windscreen is curved in two directions, suitably each direction of curvature is orthogonal to the other. Suitably the radius of curvature in one or both directions of curvature is between 1000mm and 8000mm.

Usually “surface one “of a vehicle windscreen is convex and “surface four” of the vehicle windscreen is concave.

In figure 2, the windscreen 1 has an inner facing surface 4 i.e. “surface four” of the windscreen.

Usually light from the head up display projector 9 is reflected from a portion of the inner facing surface 4 defining the first head up display region 3 towards the eye box position 11 to produce a virtual image that appears to be behind the windscreen (from the perspective of a driver of the vehicle) In some embodiments the virtual image may be produced at least in part by reflection from any of the other “surface one”, “surface two” or “surface three” of the windscreen. In some windscreens the interlayer structure joining the two glass sheets together may be suitably configured to allow some of the light from the display projector 9 to be directed towards the eye box position 11. This may be as well as, or instead of, any light reflected from any of the surfaces “surface one”, “surface two”, “surface three” or “surface four”.

In order to assess the image quality of the first head up display region 3, the windscreen is usually inspected before being installed in a vehicle. For a conventional head up display region a light source is used to irradiate the windscreen to generate a virtual image corresponding to the head up display image at the projection distance of the virtual image when the windscreen is installed in a vehicle. The display image is typically in the form of a characteristic pattern of points and lines that is distorted such that upon being reflected off the curved inner surface of the windscreen, an undistorted virtual image is produced. This virtual image is captured through the windscreen with a camera unit from a plurality of possible eye positions of a driver i.e. at different eye positions within the eye box. Using the images, the occurrence of optical effects such as distortions, ghost images as a result of multiple reflections, and the like can then be evaluated in detail for different eye positions in the eye box

When the virtual image is captured by means of a camera unit from different eye positions in the eye box, a single camera may be movably mounted, for example, on a robot arm to move the camera between the different eye positions. Alternatively, a plurality of cameras each associated with one eye position can be used. Movement during the test is then unnecessary and the cameras are, consequently, preferably mounted statically.

Images captured by the or each camera are then analysed using image processing programs well known in the art to determine a particular performance parameter for the first head up display region of the windscreen at the respective eye position in the eye box. Often this is simply referred to as a performance parameter of the windscreen. An overall particular performance parameter may be determined based on each of the particular performance parameters for respective eye box positions.

Figure 3 is used to describe how a method according to the first aspect of the present invention is carried out.

A windscreen 1 as described with reference to figures 1 and 2 is to be inspected to assess the head up display performance of the windscreen for use in an augmented reality head up display system for a vehicle where the virtual image has a first projection distance of about 10m from the eye box position. In figure 3 the axis A-A’ is aligned with the eye box position and with reference to figure 2, the first projection distance is shown as distance 1 . The windscreen 1 is held in the desired position for inspection by a suitable fixture 39. The fixture 39 ensures all measurements are made with the windscreen 1 (and subsequent windscreens to be inspected) being held at the same desired measurement position.

A light source 9’ is positioned to direct light in the direction of arrow 10’ to illuminate the first head up display region 3 of the windscreen 1.

Light from the light source 9’ is reflected off the windscreen 1 towards a camera 35. The camera 35 is positioned at an eye position in the eye box position. A virtual image 13 is produced by the light from the light source 9’ striking the inner facing surface 4 and this can be imaged by the camera 35. The virtual image 13 is produced at a first image plane that is a first distance 17 from the eye box, the first distance 17 being less than the first projection distance 19.

Light from the light source 9’ is in the form of a pattern comprising a plurality of dots and in figure 3 the camera 35 is shown imaging one such dot 41. The dot 41 may be referred to as a virtual image element.

For reference purposes only, the position of the virtual image 15 at the first projection distance 19 from the eye box position is shown in figure 3. The corresponding virtual image element dot 41 (labelled as dot 41’ in the virtual image 15) is illustrated.

The inspection method according to the present invention images the virtual image 13 at the first distance 17 which is different than the first projection distance 19, and in this embodiment the first distance 17 is less than the first projection distance 19. As figure 3 demonstrates, the windscreen 1 is inspected using a virtual image 13 that is not in the same position relative to the windscreen 1 compared to the virtual image 15 produced when the windscreen 1 is installed in a vehicle, as shown in figure 2, even though the same head up display region 3 is being illuminated to produce the virtual images 13, 15.

The light projected onto the first head up display region 3 is in the form of a distorted reference image (or pattern). The amount of distortion applied to the reference image may be determined based in part on the geometry of the windscreen and/or any other optical components used in projecting light from light source 9’ onto the first head up display region 3. As the projected image is reflected off the inner facing surface 4 of the windscreen 1, the distorted projected image is itself distorted and the virtual image 13 produced at the first image plane is ideally the same as the original undistorted reference image By assessing how much the virtual image deviates from the undistorted reference image, a performance parameter of the windscreen can be determined against a set of predetermined criteria or an applicable performance specification. In accordance with an embodiment of the present invention, the first distance 17 during the inspection of the windscreen 1 is less than the first projection distance 19. In this example the first projection distance 19 is about 10m and the first distance 17 is about 2m.

Surprisingly, the present inventors have found there is a good correlation between performance parameters determined from measurements made at the first distance 17 and corresponding performance parameters determined from measurements made at the first projection distance 19. This correlation therefore allows a performance specification to be defined for performance parameters of the first head up display region of the windscreen determined from measurements made at the first distance (and not at the first projection distance). This removes the need to make measurements at the first projection distance, thereby simplifying the inspection process because measurements only need to be made at a first distance that can be much shorter than the first projection distance.

To illustrate the correlation between a performance parameter measured where a virtual image was produced at about 2m compared with a performance parameter measured where a virtual image was produced at about 10m, reference is made to figure 4.

Figure 4 shows how the measured height of a virtual image element in a virtual image at a projection distance of about 10m (axis 31) compares with the measured height of the corresponding virtual image element in a virtual image at a projection distance of about 2m (axis 33).

As can be seen there is a good correlation This allows an appropnate performance specification to be defined at a distance of 2m (i.e. at a first distance) in order to assess the quality of the glazing. The correlation also allows an equation or correction factor to be determined to transform the height of the virtual image element measured at the first image plane to a calculated height at a second image plane (which may be at the first projection distance). If so desired, the performance specification may be based on the transformed performance parameter at the second distance (which may be the projection distance), instead of the measured performance parameter at the first distance.

Referring back to figure 3, the camera 35 is in communication with a computer 38 via suitable cabling 38a.

The computer 38 may also be in communication with the light source 9’ via suitable cabling 38b to control the pattern being projected onto the inner facing surface 4 of the windscreen 1. Different patterns may be used for windscreens for different types of vehicles.

The computer 38 includes software to analyse an image of the virtual image 13 captured by the camera 35 to determine a particular performance parameter of the head up display region 3 of the windscreen 1. This is then compared with a performance specification for the particular performance parameter at the first distance 17 to determine if the windscreen 1 has acceptable performance for use in the head up display system of the appropriate vehicle

The camera 35 may capture one or more images of the virtual image 13 at the first image plane to image the entire virtual image produced due to light being reflected from the entire first head up display region 3. The camera 35 may be positioned at different eye positions in the eye box to capture an image at each eye position. The image captured at each eye position in the eye box may then be used to determine a particular performance parameter at each respective eye box position. This is further illustrated with reference to figures 5 and 6.

With reference to figures 3, 5 and 6, in order to make measurements of the performance of the first head up display region 3 of the windscreen 1, at least the entire first head up display region 3 is illuminated with light from the light source 9’. The perimeter of the area illuminated in this example is shown by the dotted line 21 and includes the entire first head up display region 3.

Measurement of the virtual image 13 at the first image plane made with camera 35 may be a single captured image. However, due to the size of the virtual image 13 at the first image plane, multiple images are usually captured using a suitable imaging system which may include multiple cameras at different eye positions in the eye box and/or a movable camera for moving to each eye position in the eye box. In this example the camera 35 is movable to six different eye positions in the eye box and is used to capture six images 25a, 25b, 25c, 25d, 25e and 25f. Instead of a movable camera, six fixed cameras at the desired eye positions in the eye box may be used to capture the images 25a, 25b, 25c, 25d, 25e and 25f.

For a particular performance parameter, each individual image 25a, 25b, 25c, 25d, 25e and 25f may be used to determine a respective particular performance parameter for that portion of the virtual image

The six images 25a, 25b, 25c, 25d, 25e and 25f allow the entire virtual image due to reflection from the entire first head up display region 3 to be constructed.

If desired, the performance parameters may also be determined using such a constructed image of the entire virtual image due to reflection from the entire first head up display region 3.

Methods in accordance with the present invention may also be used to inspect a glazing such as a vehicle windscreen that has two (or more) head up display regions. Measurement of the performance parameters of different head up display regions of the glazing may be made using a virtual image produced at the same distance from the eye box position for each different head up display region when the glazing is installed in a vehicle. This requires suitable illumination of the different head up display regions to produce virtual images at the same distance relative to the eye box position for measurements of each different head up display region, whereas when such a glazing is installed in a vehicle, each different head up display region has a respective projection distance.

According to the present invention, such a glazing may be inspected without using a virtual image projected at the projection distance of any of the head up display regions.

For example, if a windscreen has a first head up display region for an augmented reality head up display system where a projection distance may be about 10m from an eye box position, and a second head up display region for a conventional head up display system where a projection distance may be about 2m from an eye box position, in accordance with the present invention performance parameters of the second head up display region of the glazing may be made with a virtual image produced at 2m, and performance parameters of the first head up display region of the glazing may also be made with a virtual image produced at 2m.

Although the performance parameters of the first head up display region measured using a virtual image at 2m (and not 10m) are different compared to the equivalent performance parameter when measured at 10m, as illustrated by figure 4 there is a good correlation allowing an appropriate performance specification to be determined for the performance parameters of the first head up display region when measured using a virtual image at 2m (and not at 10m).

By using a suitable virtual image at 2m from the eye box position, the performance parameters of the second head up display region are made at the projection distance for the conventional head up display system which may be desirable.

However, it is expected that the performance parameters for the second head up display region may be made using a virtual image at a different distance from the eye box position, for example Im or more than 2m and less than the projection distance of the augmented reality head up display system (i.e. 10m). As the distance of the virtual image used during a method according to the present invention approaches that of the projection distance of the augmented reality head up display system, the advantages of the present invention may be reduced.

It is advantageous when using the present invention to inspect a glazing that has at least a first and a second head up display region each having a respective projection distance from an eye box position, wherein the projection distance of the first head up display region is greater than the projection distance of the second head up display region, to inspect the glazing with a virtual image at the projection distance of the second head up display region or at a distance less than the projection distance of the second head up display region. This is particularly advantageous when the projection distance of the first head up display region is more than 5m and less than 20m, and when the projection distance of the second head up display region is less than 5m and more than Im. In other embodiments of the present invention, the above windscreen just defined having a first head up display region for an augmented reality head up display system where a projection distance is about 10m from an eye box position, and a second head up display region for a conventional head up display system where a projection distance is about 2m from an eye box position may be inspected using a virtual image produced at an image plane greater than 10m from an eye box position. This however is not preferred because previously discussed difficulties arise as the virtual image becomes further away from the eye box position.

It will also be readily apparent that a method according to the present invention may be used to inspect a glazing having more than two head up display regions, such as three or more head up display regions

The present invention has the following aspects.

Aspect 1. A method of inspecting a glazing, the glazing being configured for installing in a vehicle having a head up display projector such that in use, light from the head up display projector illuminates a first head up display region of the glazing to produce a first virtual image at a first projection distance from an eye box position, the method of inspecting the glazing comprising: (i) positioning the glazing relative to a light source; (ii) directing light from the light source to illuminate at least a portion of the first head up display region of the glazing to produce a first virtual image at a first image plane, the first image plane being a first distance from the eye box position; (iii) imaging the first virtual image at the first image plane with an imaging system to capture a first image; and (iv) using the first image of the first virtual image at the first image plane to determine at least a first performance parameter of the first head up display region of the glazing; wherein the first distance is different to the first projection distance

Aspect 2. A method according to aspect 1, wherein the first performance parameter determined at (iv) is compared with an appropriate performance specification.

Aspect 3. A method according to aspect 2, wherein the appropriate performance specification is a range for the first performance parameter at the first distance.

Aspect 4. A method according to any of the aspects 1 to 3, wherein the first projection distance is greater than 3m, more preferably greater than 5m, even more preferably greater than 7m.

Aspect 5. A method according to any of the aspects 1 to 4, wherein the first projection distance is less than 150m, more preferably less than 50m, even more preferably less than 20m, even more preferably less than 15m. Aspect 6. A method according to any of the aspects 1 to 5, wherein the first distance is less than or equal to about 4m, preferably wherein the first distance is less than or equal to about 3m, more preferably wherein the first distance is less than or equal to about 2.5m.

Aspect 7. A method according to any of the aspects 1 to 6, wherein the first distance is greater than about 0.5m, preferably greater than about Im.

Aspect 8. A method according to any of the aspects 1 to 7, wherein the first projection distance is between 7m and 150m, and the first distance is between Im and 30m with the proviso that the first distance is less than the first projection distance.

Aspect 9. A method according to any of the aspects 1 to 8, wherein the first projection distance is between 7m and 15m, and the first distance is between Im and 3m.

Aspect 10. A method according to any of the aspects 1 to 9, wherein the first head up display region is for an augmented reality head up display system.

Aspect 11. A method according to any of the aspects 1 to 10, wherein the first head up display region is about at least 5% of an area of the glazing.

Aspect 12. A method according to any of the aspects 1 to 11, wherein first head up display region is less than about 50% of an area of the glazing, preferably less than about 25% of an area of the glazing.

Aspect 13. A method according to any of the aspects 1 to 12, wherein the glazing is a windscreen.

Aspect 14. A method according to any of the aspects 1 to 13, wherein the glazing is a windscreen for a motor vehicle, a train, an aeroplane or a vehicle for use on water.

Aspect 15. A method according to any of the aspects 1 to 14, wherein the glazing comprises a first pane of glazing material joined to a second pane of glazing material by an interlayer structure comprising at least one sheet of adhesive interlayer material, the second pane of glazing material being an inner sheet for facing the interior of the vehicle when the glazing is installed in the vehicle and the first pane of glazing material being an outer sheet for facing the external environment of when the glazing is installed in the vehicle; wherein the inner sheet has a major surface facing the interior of the vehicle when the glazing is installed in the vehicle and wherein the outer sheet has outer surface for facing the external environment of the vehicle in which the glazing is installed.

Aspect 16. A method according to any of the aspects 1 to 15, wherein the imaging system comprises at least one camera. Aspect 17. A method according to any of the aspects 1 to 16, wherein the imaging system comprises at least one fixed camera for capturing an image of the first virtual image from a respective fixed eye position in the eye box.

Aspect 18. A method according to any of the aspects 1 to 17, wherein the imaging system comprises at least one movable camera for capturing an image of the first virtual image from a first eye position in the eye box, the movable camera being movable to a second eye position in the eye box to capture a different image of the first virtual image .

Aspect 19. A method according to any of the aspects 1 to 18, wherein the first image of the first virtual image is captured with a camera being positioned at the eye box position.

Aspect 20. A method according to any of the aspects 1 to 19, wherein the first image of the first virtual image is captured with a camera being positioned at a first eye position in the eye box.

Aspect 21. A method according to any of the aspects 1 to 20, wherein the eye box position has more than one eye position associated therewith.

Aspect 22. A method according to any of the aspects 1 to 21, the light source comprises a display.

Aspect 23. A method according to any of the aspects 1 to 22, wherein the light source comprises a pattern of perforations backlit by a flat light source.

Aspect 24. A method according to any of the aspects 1 to 23, wherein the first virtual image is configured to be parallel to the first virtual image at the first projection distance of the head up display system.

Aspect 25. A method according to any of the aspects 1 to 24, wherein the first distance is less than the first projection distance.

Aspect 26. A method according to any of the aspects 1 to 25, wherein the first projection distance is greater than x m, wherein x = 3, or 4, or 5, or, 6. Or 7, or 8, or 9, or 10, or 15, or 20, or 30, or 40, or 50, or 60, or 70, or 80, or 90, or 100.

Aspect 27. A method according to any of the aspects 1 to 26, wherein the first projection distance is less than m, wherein y = 110, or 100, or 90, or 80, or 70, or 60, or 50, or 40, or 30.

Aspect 28. A method according to any of the aspects 1 to 27, wherein the first projection distance is between 5m and 15m.

Aspect 29. A method according to any of the aspects 1 to 28, wherein the first distance is not greater than j m, wherein j = 5, or 4.5, or 4, or 3.5, or 3, or 2.5, or 2, or 1.5, or 1, or 0.5. Aspect 30. A method according to any of the aspects 1 to 29, wherein the first distance is at least k m, wherein k= 0.1, or 0.2, or 0.3, or 0.4, or 0.5, or 0 6, or 0.7, or 0.8, or 0.9, or 1, or 1.1, 1.2, or 1.3, or 1.4, or 1.5, or 1.6, or 1.7, or 1.8, or 1.9, or 2.

Aspect 31. A method according to any of the aspects 1 to 30, wherein the first distance is between 0.5m and 5m, more preferably between 0.5m and 4m, even more preferably between 0.5m and 3m.

Aspect 32. A method according to any of the aspects 1 to 24, wherein the first distance is greater than the first projection distance.

Aspect 33. A method according to aspect 32, wherein the first distance is greater than x ’ m, wherein x’ = 3, or 4, or 5, or, 6. Or 7, or 8, or 9, or 10, or 15, or 20, or 30, or 40, or 50, or 60, or 70, or 80, or 90, or 100.

Aspect 34. A method according to aspect 32 or aspect 33, wherein the first distance is less than y ’ m, whereiny ’ = 110, or 100, or 90, or 80, or 70, or 60, or 50, or 40, or 30.

Aspect 35. A method according to any of the aspects 32 to 34, wherein the first distance is between

5m and 15m.

Aspect 36. A method according to any of the aspects 32 to 35, wherein the first projection distance is less than or equal to j ’ m, wherein j ’ = 5, or 4.5, or 4, or 3.5, or 3, or 2.5, or 2, or 1.5, or 1, or 0.5.

Aspect 37. A method according to any of the aspects 32 to 36, wherein the first projection distance is at least k’ m, wherein k’ = 0.1, or 0.2, or 0.3, or 0.4, or 0 5, or 0.6, or 0.7, or 0.8, or 0.9, or 1, or 1.1, 1.2, or 1.3, or 1.4, or 1.5, or 1.6, or 1.7, or 1.8, or 1.9, or 2.

Aspect 38. A method according to any of the aspects 32 to 37, wherein the first projection distance is between 0.5m and 5m, more preferably between 0.5m and 4m, even more preferably between 0.5m and 3m.

Aspect 39. A method according to any of the aspects 1 to 25 or aspect 32 wherein the first projection distance is greater than 20m,

Aspect 40. A method according to aspect 39, wherein the first projection distance is greater than x ” m, wherein x ” = 30, or 40, or 50, or 60, or 70, or 80, or 90, or 100.

Aspect 41. A method according to aspect 39 or aspect 40, wherein the first projection distance is less thany ” m, wherein y” = 110, or 100, or 90, or 80, or 70, or 60, or 50, or 40, or 30. Aspect 42. A method according to any of the aspects 1 to 41, wherein the first image of the first virtual image is captured with the imaging system being positioned at the eye box position.

Aspect 43. A method according to any of the aspects 1 to 42, wherein the first image of the first virtual image is captured with a camera being positioned at the eye box position.

Aspect 44. A method according to any of the aspects 1 to 43, wherein the first image of the first virtual image is captured with a camera being positioned at a first eye position in the eye box.

Aspect 45. A method according to any of the aspects 1 to 44, wherein the first image of the first virtual image is captured at a first eye position in the eye box.

Aspect 46. A method according to aspect 45, wherein the method comprises capturing a second image of the first virtual image at the first image plane at a second eye position in the eye box and determining a first performance factor using the second image of the first virtual image.

Aspect 47. A method according to any of the aspects 1 to 46, wherein a plurality of images of the first virtual image are captured, each image being captured at a different eye position in the eye box

Aspect 48. A method according to aspect 48, wherein each image in the plurality of images is used to determine a respective first performance parameter.

Aspect 49. A method according to aspect 47 or aspect 48, wherein each image is used to construct an image of the first virtual image, and the constructed image of the first virtual image is used to determine a first performance parameter.

Aspect 50. A method according to any of the aspects 1 to 49, wherein the glazing comprises a first pane of glazing material joined to a second pane of glazing material by an interlayer structure comprising at least one sheet of adhesive interlayer material, the second pane of glazing material being an inner sheet for facing the interior of the vehicle when the glazing is installed in the vehicle, the inner sheet having an inner surface facing the interior of the vehicle when the glazing is installed in the vehicle, wherein the first virtual image that is produced comprises light from at least reflection from the inner surface of the inner sheet.

Aspect 51. A method according to aspect 50, wherein the first pane of glazing material is an outer sheet for facing the external environment of the vehicle in which the glazing is installed, wherein the outer sheet has an outer surface for facing the external environment of the vehicle in which the glazing is installed.

Aspect 52. A method according to aspect 50, or aspect 51, wherein the first virtual image that is produced comprises light from at least reflection from the interlayer structure.

Aspect 53. A method according to any of the aspects 50 to 52, wherein the first virtual image that is produced in these embodiments comprises light from at least reflection from the outer surface.

Aspect 54. A method according to any of the aspects 1 to 53, wherein the imaging system comprises a first camera at a first eye position in the eye box to capture the first image of the first virtual image and a second camera at a second eye position in the eye box to capture a second image of the first virtual image.

Aspect 55. A method according to any of the aspects 1 to 53, wherein the imaging system is movable relative to the glazing to capture the first image with the imaging system at a first position relative to the glazing and to capture a second image with the imaging system at a second position relative to the glazing.

Aspect 56. A method according to aspect 55, wherein the first image is captured at a first eye position in the eye box.

Aspect 57. A method according to aspect 55 or aspect 57, wherein the imaging system is moved to the second position relative to the glazing.

Aspect 58. A method according to any of the aspects 55 to 57, wherein the second image is captured at a second position in the eye box.

Aspect 59. A method according to any of the aspects 55 to 58, wherein a plurality of images is captured to construct an image of the entire first virtual image.

Aspect 60. A method according to any of the aspects 1 to 59, wherein light from the light source is in the form of a pattern, preferably comprising at least one dot and/or at least one line.

Aspect 61. A method according to aspect 60, wherein the pattern is specific for inspecting a glazing intended for a particular model of vehicle.

Aspect 62. A method according to any of the aspects 1 to 61, wherein light from the light source is in the form of a pattern and the first virtual image of the pattern at the first image plane is distorted by the glazing, wherein the first virtual image distorted by the glazing is compared against a reference image of the pattern when determining the performance parameter of the glazing.

Aspect 63. A method according to aspect 62, wherein is the reference image is an undistorted image which is then distorted for projection onto the glazing being inspected.

Aspect 64. A method according to any of the aspects 1 to 63, wherein the first performance parameter of the first head up display region of the glazing is determined using only the first image of the first virtual image

Aspect 65. A method according to aspect 64, wherein the first image of the first virtual image is captured with the imaging system being positioned at a first eye position in the eye box.

Aspect 66. A method according to any of the aspects 1 to 65, wherein during (ii) light from the light source illuminates at least the entire first head up display region.

Aspect 67. A method according to aspect 66, wherein at (iii) the entire first virtual image from the entirely illuminated first head up display region is imaged and the captured first image is an image of the entire first virtual image.

Aspect 68. A method according to aspect 66, wherein only a portion of the entire virtual image from the entirely illuminated first head up display region is captured as the first image at (iii).

Aspect 69. A method according to aspect 66, wherein an image of the entire virtual image from the first head up display region is constructed from a plurality of images, each image in the plurality of images being of a different portion of the entire virtual image from the first head up display region.

Aspect 70. A method according to any of the aspects 1 to 65, wherein the performance the entire first head up display region is determined by carrying out steps (ii) and (iii) a plurality of times to illuminate a plurality of different portions of the first head up display region of the glazing.

Aspect 71. A method according to aspect 70, wherein each portion of the first head up display region is illuminated separately.

Aspect 72. A method according to aspect 70 or aspect 71, wherein each different portion is used to determine a respective first performance parameter.

Aspect 73. A method according to any of the aspects 70 to 72, wherein each respective first image from the different illuminated portions of the first head up display region is used to construct an image of the entire virtual image from the first head up display region. Aspect 74. A method according to aspect 73, wherein the image of the entire virtual image from the first head up display region so constructed is used to determine the first performance parameter of the first head up display region of the glazing.

Aspect 75. A method according to any of the aspects 1 to 74, wherein the glazing is configured for installing in the vehicle such that in use, light from the head up display projector illuminates a second head up display region of the glazing to produce a virtual image at a second projection distance from the eye box position, wherein the second projection distance is less than the first projection distance.

Aspect 76. A method according to aspect 75, wherein the method of inspecting the glazing comprises inspecting the second head up display region to determine at least a first performance parameter of the second head up display region of the glazing.

Aspect 77. A method according to aspect 76, wherein method of inspecting the second head up display region comprises directing light from the light source or another light source to illuminate at least a portion of the second head up display region of the glazing to produce a second virtual image at a second image plane, the second image plane being at a second distance from the eye box position; imaging the second virtual image at the second image plane with an imaging system to capture a first image of the second virtual image; and using the first image of the second virtual image to determine at least a first performance parameter of the second head up display region of the glazing.

Aspect 78. A method according to aspect 77, wherein the first performance parameter of the second head up display region of the glazing is compared with an appropriate performance specification

Aspect 79. A method according to any of the aspects 75 to 78, wherein the second distance of the second image plane from the eye box position is the same as the first distance of the first image plane from the eye box position.

Aspect 80. A method according to any of the aspects 75 to 79, wherein the second distance is the same as the second projection distance.

Aspect 81. A method according to any of the aspects 75 to 80, wherein the first projection distance is between 5m and 20m and the second projection distance is between Im and 5m.

Aspect 82. A method according to any of the aspects 75 to 81, wherein the first head up display region of the glazing has a first area and the second head up display region of the glazing has a second area, wherein the first area is greater than the second area. Aspect 83. A method according to aspect 82, wherein the first area is at least 1.5 times the area of the second area, preferably 2 times the area of the second area, more preferably 3, or 4, or 5, or 6, or 7, or 8, or 9, or 10 times the area of the second area.

Aspect 84. A method according to aspect 82 or aspect 83, wherein the first area is less than 20 times the area of the second area.

Aspect 85. A method according to any of the aspects 75 to 84, wherein the first region is for an augmented reality head up display system and the second region is for a conventional head up display system.

Aspect 87. A method according to any of the claims 1 to 74, wherein the method is used to inspect a glazing that is configured for installing in the vehicle such that in use, light from the head up display projector illuminates a second head up display region of the glazing to produce a second virtual image at a second projection distance from the eye box position, wherein the second projection distance is greater than the first projection distance.

Aspect 88. A method according to aspect 87, wherein the method of inspecting the glazing comprises inspecting the second head up display region to determine at least a first performance parameter of the second head up display region of the glazing.

Aspect 89. A method according to aspect 88, wherein method of inspecting the second head up display region comprises directing light from the light source or another light source to illuminate at least a portion of the second head up display region of the glazing to produce a second virtual image at a second image plane, the second image plane being at a second distance from the eye box position; imaging the second virtual image at the second image plane with an imaging system to capture a first image of the second virtual image; and using the first image of the second virtual image to determine at least a first performance parameter of the second head up display region of the glazing.

Aspect 90. A method according to aspect 89, wherein the first performance parameter of the second head up display region of the glazing is compared with an appropriate performance specification

Aspect 91. A method according to any of the claims 87 to 90, wherein the second distance of the second image plane from the eye box position is the same as the first distance of the first image plane from the eye box position.

Aspect 92. A method according to any of the aspects 87 to 91, wherein the first distance is the same as the second projection distance. Aspect 93. A method according to any of the aspects 1 to 92, wherein the method includes a calibration step such that during (iv), the first performance parameter measured at the first image plane can be transformed to a corresponding first performance parameter at the first projection distance or at another projection distance from the eye box position using at least a first correction factor determined during the calibration step.

Aspect 94. A method according to aspect 93, wherein the first correction factor is determined using ray tracing or measurement of the first performance parameter of a reference virtual image produced at the first image plane and the first projection distance or the another distance.

Aspect 95. A method according to aspect 94 or aspect 95, wherein the first correction factor includes a factor for transforming at least one of ghosting, distortion, magnification, aspect ratio and displacement.

Aspect 96. A method according to any of the aspects 1 to 95, wherein the first performance parameter of the first head up display region of the glazing relates to ghosting, distortion, magnification, aspect ratio or displacement.

Aspect 97. A method according to any of the aspects 1 to 96, wherein the first virtual image at the first distance is configured to be parallel to the first virtual image at the first projection distance of the head up display system.

Aspect 98. A method according to any of the aspects 1 to 97, wherein the first virtual image at the first distance is configured to be parallel to the eye box position.

Aspect 99. A method according to any of the aspects 1 to 98, wherein when the glazing is installed in the vehicle and light from the head up display projector illuminates the first head up display region of the glazing to produce the first virtual image at the first projection distance from the eye box position, the first virtual image at the first projection distance from the eye box position is part of an inclined virtual image wherein the inclined virtual image is inclined relative to the eye box position.

Aspect 100. A method according to any of the aspects 1 to 99, wherein when the glazing is installed in the vehicle, in use light from the head up display projector also illuminates a second head up display region of the glazing to produce a second virtual image at a second projection distance from an eye box position.

Aspect 101. A method according to any of the aspects 1 to 100, wherein the first virtual image at the first projection distance is part of an inclined virtual image wherein the inclined virtual image is inclined relative to the eye box position. Aspect 102. A method according to any of the aspects 1 to 101, wherein the first virtual image at the first projection distance is part of an inclined virtual image set so as to incline forward with respect to a vertical direction of the vehicle.

Aspect 103. Apparatus for inspecting a glazing, the glazing being configured for installing in a vehicle having a head up display projector such that in use, light from the head up display projector illuminates a first head up display region of the glazing to produce a first virtual image at a first projection distance from an eye box position; the apparatus comprising: a fixture, a light source, an imaging system and a computer; the fixture being arranged relative to the light source and configured to hold the windscreen during an inspection measurement such that light from the light source strikes the glazing to produce a virtual image at a first image plane, the first image plane being at a first distance from the eye box position; the imaging system being arranged relative to the glazing during the inspection step to capture an image of the virtual image at the first image plane through the glazing; and wherein the computer has a program for analysing the captured image of the virtual image at the first image plane to determine at least a first performance parameter of the glazing, wherein the first image plane is at a different position than the first projection distance.

Aspect 104. Apparatus according to aspect 103, wherein the imaging system is positioned at the eye box position.

Aspect 105. Apparatus according to aspect 103 or aspect 104, wherein the imaging system comprises at least one fixed camera and/or at least one movable camera.

Claims

1. A method of inspecting a glazing for use in a head up display system, the glazing being configured for installing in a vehicle having a head up display projector such that in use, light from the head up display projector illuminates a first head up display region of the glazing to produce a first virtual image at a first projection distance from an eye box position, the method of inspecting the glazing comprising:

(i) positioning the glazing relative to a light source;

(ii) directing light from the light source to illuminate at least a portion of the first head up display region of the glazing to produce a first virtual image at a first image plane, the first image plane being a first distance from the eye box position;

(iii) imaging the first virtual image at the first image plane with an imaging system to capture a first image of the virtual image at the first image plane; and

(iv) using the first image of the first virtual image at the first image plane to determine at least a first performance parameter of the first head up display region of the glazing; wherein the first distance is different to the first projection distance.

2. A method according to claim 1, wherein the first performance parameter of the first head up display region of the glazing is compared with an appropriate performance specification.

3. A method according to claim 1 or claim 2, wherein the first distance is less than the first projection distance.

4. A method according to any of the preceding claims, wherein the first projection distance is greater than 3m, preferably greater than 5m, more preferably greater than 7m.

5. A method according to any of the preceding claims, wherein the first projection distance is less than 150m, more preferably less than 50m, even more preferably less than 20m, even more preferably less than 15m.

6. A method according to any of the preceding claims, wherein the first distance is less than 4m, preferably less than 3m, more preferably less than 2.5m.

7. A method according to any of the preceding claims, wherein the first distance is greater than 0.5m, preferably greater than Im.

8. A method according to any of the preceding claims, wherein the first projection distance is between 7m and 15m, and wherein the first distance is between Im and 3m.

9. A method according to claim 1 or claim 2, wherein the first distance is greater than the first projection distance.

10. A method according to claim 9, wherein the first distance is between 5m and 15m and/or wherein the first projection distance is between 0.5m and 5m.

11. A method according to any of the preceding claims, wherein the first head up display region is for an augmented reality head up display system.

12. A method according to any of the preceding claims, wherein the first head up display region is about at least 5% of an area of the glazing.

13. A method according to any of the preceding claims, wherein the first head up display region is less than about 50% of an area of the glazing, more preferably less than about 25% of an area of the glazing.

14. A method according to any of the preceding claims, wherein during (ii) light directed from the light source illuminates at least the entire first head up display region.

15. A method according to claim 14, wherein at (iii) the entire virtual image from the first head up display region is imaged to produce the first image.

16. A method according to claim 14, wherein after step (ii) the first virtual image is imaged to capture at least a second image, the second image being of a different portion of the first virtual image than the first image, preferably wherein the first image at least partially overlaps the second image.

17. A method according to claim 16, wherein for each of the first and second images, a respective first performance parameter is determined.

18. A method according to any of the preceding claims, wherein the performance of the entire first head up display region is determined by carrying out steps (ii) and (iii) a plurality of times to illuminate a plurality of different portions of the first head up display region of the glazing.

19. A method according to claim 18, wherein each portion of the first head up display region is illuminated separately.

20. A method according to claim 18 or claim 19, wherein each different portion is used to determine a respective first performance parameter.

21. A method according to any of the claims 1 to 13, wherein steps (ii) and (iii) are repeated a plurality of times such that the plurality of first images so produced are used to construct an image of the entire first virtual image from the first head up display region.

22. A method according to any of the preceding claims wherein the glazing is configured for installing in the vehicle such that in use, light from the head up display projector illuminates a second head up display region of the glazing to produce a second virtual image at a second projection distance from the eye box position, wherein the second projection distance is different than the first projection distance.

23. A method according to claim 22, comprising inspecting the second head up display region to determine at least a first performance parameter of the second head up display region of the glazing.

24. A method according to claim 23, wherein the method of inspecting the second head up display region comprises directing light from the light source or another light source to illuminate at least a portion of the second head up display region of the glazing to produce a second virtual image at a second image plane, the second image plane being at a second distance from the eye box position; imaging the second virtual image at the second image plane with an imaging system to capture a first image of the second virtual image; and using the first image of the second virtual image to determine at least a first performance parameter of the second head up display region of the glazing.

25. A method according to claim 24, wherein the first performance parameter of the second head up display region of the glazing is compared with an appropriate performance specification.

26. A method according to claim 24 or claim 25, wherein the second distance of the second image plane from the eye box position is the same as the first distance of the first image plane from the eye box position.

27. A method according to any of the claims 22 to 26, wherein the first distance is the same as the second projection distance.

28. A method according to any of the claims 22 to 27, wherein the second projection distance is greater than the first projection distance.

29. A method according to any of the claims 22 to 27, wherein the second projection distance is less than the first projection distance.

30. A method according to any of the claims 22 to 27, wherein the first projection distance is between 5m and 20m and the second projection distance is between Im and 5m.

31. A method according to any of the preceding claims, wherein the first performance parameter of the first head up display region of the glazing relates to ghosting, distortion, magnification, aspect ratio or displacement.

32. A method according to any of the preceding claims, wherein the first virtual image at the first projection distance is part of an inclined virtual image wherein the inclined virtual image is inclined relative to the eye box position.

33. A method according to any of preceding claims, wherein the first virtual image at the first projection distance is part of an inclined virtual image set so as to incline forward with respect to a vertical direction of the vehicle.

34. Apparatus for inspecting a glazing, the glazing being configured for installing in a vehicle having a head up display projector such that in use, light from the head up display projector illuminates a first head up display region of the glazing to produce a first virtual image at a first projection distance from an eye box position; the apparatus comprising: a fixture, a light source, an imaging system and a computer; the fixture being arranged relative to the light source and configured to hold the windscreen during an inspection measurement such that light from the light source strikes the glazing to produce a virtual image at a first image plane, the first image plane being at a first distance from the eye box position; the imaging system being arranged relative to the glazing during the inspection step to capture an image of the virtual image at the first image plane through the glazing; and wherein the computer has a program for analysing the captured image of the virtual image at the first image plane to determine at least a first performance parameter of the glazing, wherein the first image plane is at a different position than the first projection distance.

35. Apparatus according to claim 34, wherein the imaging system is positioned at the eye box position.