WO2008107720A1 - Imagerie laser améliorée en couleur - Google Patents

Imagerie laser améliorée en couleur Download PDF

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Publication number
WO2008107720A1
WO2008107720A1 PCT/GB2008/050157 GB2008050157W WO2008107720A1 WO 2008107720 A1 WO2008107720 A1 WO 2008107720A1 GB 2008050157 W GB2008050157 W GB 2008050157W WO 2008107720 A1 WO2008107720 A1 WO 2008107720A1
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WO
WIPO (PCT)
Prior art keywords
camera
laser scanner
colour
mounting device
terrestrial
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Application number
PCT/GB2008/050157
Other languages
English (en)
Inventor
Peter David White
Richard Raimes Jones
Original Assignee
Geospatial Research Limited
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Filing date
Publication date
Application filed by Geospatial Research Limited filed Critical Geospatial Research Limited
Publication of WO2008107720A1 publication Critical patent/WO2008107720A1/fr

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
    • G01S17/88—Lidar systems specially adapted for specific applications
    • G01S17/89—Lidar systems specially adapted for specific applications for mapping or imaging
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16M—FRAMES, CASINGS OR BEDS OF ENGINES, MACHINES OR APPARATUS, NOT SPECIFIC TO ENGINES, MACHINES OR APPARATUS PROVIDED FOR ELSEWHERE; STANDS; SUPPORTS
    • F16M11/00—Stands or trestles as supports for apparatus or articles placed thereon ; Stands for scientific apparatus such as gravitational force meters
    • F16M11/02—Heads
    • F16M11/04—Means for attachment of apparatus; Means allowing adjustment of the apparatus relatively to the stand
    • F16M11/06—Means for attachment of apparatus; Means allowing adjustment of the apparatus relatively to the stand allowing pivoting
    • F16M11/12—Means for attachment of apparatus; Means allowing adjustment of the apparatus relatively to the stand allowing pivoting in more than one direction
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16M—FRAMES, CASINGS OR BEDS OF ENGINES, MACHINES OR APPARATUS, NOT SPECIFIC TO ENGINES, MACHINES OR APPARATUS PROVIDED FOR ELSEWHERE; STANDS; SUPPORTS
    • F16M11/00—Stands or trestles as supports for apparatus or articles placed thereon ; Stands for scientific apparatus such as gravitational force meters
    • F16M11/02—Heads
    • F16M11/04—Means for attachment of apparatus; Means allowing adjustment of the apparatus relatively to the stand
    • F16M11/06—Means for attachment of apparatus; Means allowing adjustment of the apparatus relatively to the stand allowing pivoting
    • F16M11/10—Means for attachment of apparatus; Means allowing adjustment of the apparatus relatively to the stand allowing pivoting around a horizontal axis
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16M—FRAMES, CASINGS OR BEDS OF ENGINES, MACHINES OR APPARATUS, NOT SPECIFIC TO ENGINES, MACHINES OR APPARATUS PROVIDED FOR ELSEWHERE; STANDS; SUPPORTS
    • F16M11/00—Stands or trestles as supports for apparatus or articles placed thereon ; Stands for scientific apparatus such as gravitational force meters
    • F16M11/20—Undercarriages with or without wheels
    • F16M11/2007—Undercarriages with or without wheels comprising means allowing pivoting adjustment
    • F16M11/2014—Undercarriages with or without wheels comprising means allowing pivoting adjustment around a vertical axis
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16M—FRAMES, CASINGS OR BEDS OF ENGINES, MACHINES OR APPARATUS, NOT SPECIFIC TO ENGINES, MACHINES OR APPARATUS PROVIDED FOR ELSEWHERE; STANDS; SUPPORTS
    • F16M11/00—Stands or trestles as supports for apparatus or articles placed thereon ; Stands for scientific apparatus such as gravitational force meters
    • F16M11/20—Undercarriages with or without wheels
    • F16M11/2085—Undercarriages with or without wheels comprising means allowing sideward adjustment, i.e. left-right translation of the head relatively to the undercarriage
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16M—FRAMES, CASINGS OR BEDS OF ENGINES, MACHINES OR APPARATUS, NOT SPECIFIC TO ENGINES, MACHINES OR APPARATUS PROVIDED FOR ELSEWHERE; STANDS; SUPPORTS
    • F16M11/00—Stands or trestles as supports for apparatus or articles placed thereon ; Stands for scientific apparatus such as gravitational force meters
    • F16M11/20—Undercarriages with or without wheels
    • F16M11/2092—Undercarriages with or without wheels comprising means allowing depth adjustment, i.e. forward-backward translation of the head relatively to the undercarriage
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01C—MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
    • G01C11/00—Photogrammetry or videogrammetry, e.g. stereogrammetry; Photographic surveying
    • G01C11/02—Picture taking arrangements specially adapted for photogrammetry or photographic surveying, e.g. controlling overlapping of pictures
    • G01C11/025—Picture taking arrangements specially adapted for photogrammetry or photographic surveying, e.g. controlling overlapping of pictures by scanning the object
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01C—MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
    • G01C15/00—Surveying instruments or accessories not provided for in groups G01C1/00 - G01C13/00
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03B—APPARATUS OR ARRANGEMENTS FOR TAKING PHOTOGRAPHS OR FOR PROJECTING OR VIEWING THEM; APPARATUS OR ARRANGEMENTS EMPLOYING ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ACCESSORIES THEREFOR
    • G03B17/00—Details of cameras or camera bodies; Accessories therefor
    • G03B17/56—Accessories
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03B—APPARATUS OR ARRANGEMENTS FOR TAKING PHOTOGRAPHS OR FOR PROJECTING OR VIEWING THEM; APPARATUS OR ARRANGEMENTS EMPLOYING ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ACCESSORIES THEREFOR
    • G03B17/00—Details of cameras or camera bodies; Accessories therefor
    • G03B17/56—Accessories
    • G03B17/561—Support related camera accessories
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03B—APPARATUS OR ARRANGEMENTS FOR TAKING PHOTOGRAPHS OR FOR PROJECTING OR VIEWING THEM; APPARATUS OR ARRANGEMENTS EMPLOYING ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ACCESSORIES THEREFOR
    • G03B17/00—Details of cameras or camera bodies; Accessories therefor
    • G03B17/56—Accessories
    • G03B17/566—Accessory clips, holders, shoes to attach accessories to camera
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03B—APPARATUS OR ARRANGEMENTS FOR TAKING PHOTOGRAPHS OR FOR PROJECTING OR VIEWING THEM; APPARATUS OR ARRANGEMENTS EMPLOYING ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ACCESSORIES THEREFOR
    • G03B37/00—Panoramic or wide-screen photography; Photographing extended surfaces, e.g. for surveying; Photographing internal surfaces, e.g. of pipe
    • G03B37/02—Panoramic or wide-screen photography; Photographing extended surfaces, e.g. for surveying; Photographing internal surfaces, e.g. of pipe with scanning movement of lens or cameras
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
    • G01S17/86—Combinations of lidar systems with systems other than lidar, radar or sonar, e.g. with direction finders
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
    • G01S7/481—Constructional features, e.g. arrangements of optical elements

Definitions

  • the present invention relates to colour enhanced laser imagery and in particular to an apparatus and method applicable to a technique known as True Colour Terrestrial Laser Scanning.
  • TLS Terrestrial Laser Scanning
  • Another method of improving the usefulness of TLS images is to take, from arbitrary positions, a number of colour digital photographs of the object which has been the subject of the laser scan and map the colour photographs onto the laser scan.
  • This technique requires complex mapping techniques, and the quality of the results is variable.
  • Another method of acquiring colour information that can be applied to the laser scan point cloud is to use on-board video mounted inside the laser scanner device.
  • Such devices are available commercially under the brand names Leica® and Trimble®.
  • the cameras used for this method are of significantly lower quality than separate digital Single Lens Reflex (SLR) cameras, and the resultant images are of lower resolution and poorer colour precision.
  • SLR Single Lens Reflex
  • TCTLS True Colour Terrestrial Laser Scanning
  • digital colour photographs are taken of the object which is the subject of the survey.
  • the photographic images are then mapped onto the point cloud resulting from the laser scan producing a true colour three dimensional model which is much more interpretable than a TLS image.
  • a number of TCTLS devices have been developed.
  • One such device includes a digital camera which is mounted on top of a laser scanner and takes digital photographs of the subject while, or immediately after the scan is taking place.
  • Such a device is available commercially under the brand name Riegl ®.
  • complex image mapping software is required to map the colour image information from the digital photograph onto the point cloud resulting from the laser scan. Since the digital camera and laser beam are not collinear, a source of error is introduced during the mapping. Typically, these devices are expensive.
  • the present invention seeks to provide a TCTLS system at much lower cost than those systems currently known.
  • the present invention provides a particularly simple and economical solution to the problem of providing true colour terrestrial laser scans.
  • Camera mounts can be provided so that any digital camera having suitable picture quality may be used.
  • the cost of the equipment required can be reduced drastically.
  • the colour mapping in the true colour terrestrial laser scan is very accurate. It does not suffer from some of the in-built registration problems which are encountered by some known systems, as the optical centres of the laser and the camera are coincident.
  • Figure 1 is a schematic representation of a camera mounting bracket
  • FIG 2 is a schematic representation of the camera mounting bracket illustrated in Figure 1;
  • Figure 3a is a schematic representation of a terrestrial laser scanner mounted on a tripod by means of a tribrach
  • Figure 3b is a schematic representation of a digital camera mounted on a tripod by means of a camera mounting bracket according to the invention, the bracket being attached to the tripod by means of a tribrach
  • Figure 4 is a schematic representation of the camera mounting bracket illustrated in Figures 1 and 2 with a camera mounted thereon,
  • Figure 5 is an illustration of the coordinate system of a rectified plane
  • Figure 6 illustrates the projections of lines of constant azimuth and inclination onto a vertical plane
  • Figure 7 illustrates the projections of lines of constant azimuth and inclination onto an inclined plane with the plane inclined upwards
  • Figure 8 illustrates the projections of lines of constant azimuth and inclination onto an inclined plane with the plane inclined downwards
  • Figure 9 illustrates the relationship between the laser scanner and the virtual image plane in the case where the lens is pointing horizontally.
  • a camera mounting bracket 1 The bracket is designed for attachment to a tribrach which is itself mounted on a tripod in normal use. It is common practice to mount surveying equipment on a tribrach, and in this particular case a laser scanner would also be mountable on the tribrach.
  • the bracket 1 includes a base 2, which itself comprises a lower plate 3 from which depend three elements 5 of a locking arrangement.
  • the elements 5 are so shaped and located as to engage with corresponding elements in a tribrach.
  • Such tribrachs are well known in the field and as such the detail of the locking arrangement will not be described in detail.
  • the base 2 further includes an upper element 4 which is arranged to rotate with respect to the lower plate 3. Friction elements (not shown) are located between the upper and lower plates 3, 4. Due to the friction elements in the absence of a turning moment applied to the upper plate, there is no relative movement between the said upper and lower plates 3, 4.
  • Extending from the upper plate 4 is a tubular element 6 which includes a slot 6a.
  • a threaded screw 8 provided with a knob 9 extends through the slot 6a and into a shaft 7.
  • the bracket 1 further includes a plate 11.
  • the shaft 7 extends downwardly from an end plate 10 to which the plate 11 is attached by means of three bolts 13a, 13b and 13c, so that in use the plate 11 is cantilevered off the shaft 7 which is held securely in position in the tubular element 6.
  • the plate 11 includes a slot 12 which extends along the longitudinal centre line of the plate 11.
  • An L-sha ⁇ ed bracket 14 is mounted slidably on the upper surface of the plate 11.
  • a part 16 of the bracket 14 lies on the upper surface of the plate 11.
  • This part 16 is provided with a threaded bore 19 which is aligned with the slot 12.
  • a threaded screw 18 co-operates with the threaded bore to lock the bracket 14 in a desired position on the plate 11.
  • the free end of the screw 18 is provided with a knob 17 which provides for the easy slackening and tightening of the screw 18 and hence the locking of the bracket 14 in a desired position on the plate 11, or the releasing of the bracket 14 from a position on the plate 11.
  • the assembly 20 comprises a plate 21 which is pivotally attached to the upwardly extending part 15 of the bracket 14 by means of a threaded screw 26 which engages with a correspondingly threaded bore 24 in an element 24a extending from the plate 21.
  • the screw 26 passes through an unthreaded bore 25 located in the part 15 of the bracket 14. Turning the threaded screw 26 in one direction by means of the knob 27 causes the plate 21 to be pulled against the surface of the part 15 such that friction between the part 15 and the element 24a prevents rotation between the part 15 and the plate 21.
  • the plate 21 includes a slot 22 at one end of which includes an opening 23.
  • a threaded screw comprising a threaded element 30a, a knob 32 and a portion of reduced diameter 31 is located in the slot 22.
  • the opening 23 is of a dimension which allows the threaded element 30a to pass therethrough.
  • the portion of reduced diameter 31 slides in the slot 22.
  • the specification of the threaded element 30a which in the present example is a % inch Whitworth thread provides for the said element to attach to a standard tripod mount of an SLR camera.
  • a conventional TLS scanner 36 is mounted on a tribrach 35 on a tripod 34.
  • Cross-hairs 37 on the side of the scanner 36 mark a line that passes through the optical centre of the scanner.
  • a camera 30 is mounted on the plate 21.
  • a TCTLS image is created by first performing a laser scan of an ob j ect, for example a cliff face, using a conventional TLS scanner mounted on a tribrach on a tripod.
  • the Laser Ace 600 supplied by Measurement Devices Ltd is one such suitable scanner.
  • the TLS scanner is removed from the tribrach and the camera mounting bracket 1 is attached thereto.
  • the optical centres of the camera and the laser of the TLS scanner are coincident.
  • the tripod mount of an SLR camera is usually aligned with the optical centre of the camera in one axis.
  • the bracket 1 provides for the optical centre of the camera attached to plate 21 to be aligned with the optical centre of the laser of the TLS scanner. This is achieved by performing a calibration routine.
  • Alignment in the X axis is achieved by aligning the SLR camera with a near ob j ect and a distant ob j ect.
  • the bracket 14 is then turned about shaft 7 to pan the SLR camera. If during panning of the camera 30 there is movement between the near and far objects then the camera must be moved along the path defined by slot 22 until a point is reached where there is no movement between the near and far objects.
  • Alignment in the Z axis is achieved by measurement.
  • the TLS scanner is attached to the tripod by means of the same tribrach on which the base 2 sits, on the TLS scanner the distance from the bottom edge of the lower plate 3 to the optical centre of the TLS scanner can be measured.
  • the knob 9 is turned to slacken screw 8 in order that the bracket 11 may be moved up or down until the distance between the optical centre of the camera and the bottom edge of the lower plate 3 is equal to the distance between the optical centre of the TLS scanner and the bottom of its mounting plate.
  • the knob 9 is then turned to tighten the screw 8 against the shaft 7 thereby locking the bracket 11 in the desired position.
  • Alignment in the Y axis is achieved by turning the knob 27 to slacken screw 26 in order that the plate 21 may be pivoted about the screw 26 such that the SLR camera is pointing downward towards the plate 11.
  • the knob 27 is then turned to tighten the screw 26 thereby locking the plate 21 in position.
  • the knob 17 is then turned to slacken screw 18 in order that the bracket 14 (and SLR camera mounted thereon) may be moved longitudinally with respect to the plate 11 along the path defined by slot 12.
  • the bracket 14 is moved until the cross (+) on the lens of the SLR camera, which defines the optical centre of the camera is aligned with the central pin 13b.
  • an image of a desired object is captured first using a TLS scanner mounted on a tribrach which is itself mounted on a tripod.
  • the TLS scanner is then removed from the tribrach and the camera mounting bracket is attached to the tribrach.
  • the calibration routine described above may be performed prior to the apparatus being brought to the field, in which case all that the surveyor need do is take pictures using the camera. If the object cannot be photographed using one picture, it will be necessary to pan and/or tilt the camera so that sufficient pictures can be taken to capture the whole object.
  • the bracket 1 provides for both panning of the camera in the horizontal direction and tilting of the camera in the vertical direction. Panning in the horizontal is achieved by rotating the bracket 14 with respect to the base 2. Tilting in the vertical is achieved by turning the knob 27 to slacken off the screw 26. The plate 21 may then be rotated about the screw 26.
  • the camera mounting bracket may be provided with actuators such as stepper motors to rotate the camera in the vertical and horizontal planes. Actuators may also be used to control the camera mounting bracket during the calibration procedure.
  • the intrinsic parameters required to rectify the image to achieve the pinhole camera model are usually effective focal length, scale factor and image centre (principal point).
  • the images can be calibrated and rectified such that they appear to have been captured using a pinhole camera using known tools.
  • One such tool is Bouguet's Camera Calibration Toolbox for Matlab.
  • Another tool which again is freely distributed on the internet, is Vezhnevets and Velizhev's GML C++ Camera Calibration Toolbox (v. 0.31 or otherwise).
  • Vezhnevets and Velizhev's toolbox was chosen to perform the camera calibration and image rectification necessary before the photographic images could be registered with the laser scan point cloud.
  • FIG. 5 illustrates the coordinate system of the rectified image plane, where u and v are the horizontal and vertical pixel coordinates, respectively, measured from the origin at the top left corner of the image, as is the convention in computer imaging.
  • U and V refer to the total number of horizontal and vertical pixels in the image.
  • the laser scanner is an inherently spherical system using polar coordinates, whereas the camera sensor is a plane.
  • the behaviour of the scanner-camera system is described in greater detail with reference to Figures 6 to 8.
  • the laser scanner measures the azimuth angle as the scanner rotates about the vertical axis.
  • the azimuth is, therefore, the angle between the azimuth zero line in the horizontal plane passing through the scanner centre and the projection of the subject point onto the same plane. This is not the same as the horizontal angle between the vertical plane passing through the azimuth zero line and the point being scanned.
  • the scanner measures the inclination angle with respect to the horizontal plane passing through the scanner centre. The inclination is simply the direct angle between the aforementioned plane and the point being scanned.
  • the interaction of the laser scanner and the camera can be understood by imagining the projections of the lines of latitude and longitude onto a virtual plane by straight lines passing through the centre of the sphere. If the plane is vertical, the lines of latitude above the "equator" map to upwards curving lines on the plane, and those below the equator map to downwards curving lines. The lines of longitude, however, map to vertical lines on the plane as illustrated in Figure 6. If the plane is now tilted upwards, the projected lines of latitude now all curve upwards, as long as the bottom of the virtual plane is above the equatorial plane. The projections of the lines of longitude remain straight, but splay out towards the bottom of the plane as illustrated in Figure 7. If the plane is tilted downwards, the projected lines of latitude curve downwards and the projections of the lines of latitude splay out towards the top of the plane as illustrated in Figure 8.
  • the scanner-camera system conforms to the behaviour described with reference to Figures 6 to 8, with the virtual image plane corresponding to the camera's sensor.
  • the virtual plane in Figure 6 is vertical, this corresponds to the case in which the camera's sensor is vertical, i.e. the longitudinal axis of the camera's lens is pointing horizontally.
  • the virtual plane is inclined, this corresponds to the situation in which the camera is tilted about a horizontal line passing through the laser-beam detector/camera optical centre.
  • Figure 9 illustrates the relationship between the laser scanner and the virtual image plane in the case where the lens is pointing horizontally.
  • the laser scanner centre and the virtual image plane are separated by a virtual distance, d, perpendicular to the plane.
  • ⁇ c is the angle from the azimuth zero line to the centre of the virtual image plane, and u' and v' define an alternative image coordinate system with respect to an origin at the centre of the virtual image plane.
  • the registration of a set of photographs with its associated point cloud is carried out using a set of tools created in Matlab7.
  • the set of tools comprises nine individual programs collectively controlled through a common Graphical User Interface (GUI).
  • GUI Graphical User Interface
  • the first tool, cloud_load.m loads a .txt file containing the point data in the following format:
  • the undistorted images in .jpg format, are loaded using image_load.m.
  • the user is asked how many images are to be mapped and the program reads and stores the 8-bit colour intensities for each pixel.
  • map.m which solves the set of three simultaneous equations for each image, registers the images to the point cloud using the two mapping equations (i) and (11), and combines the colour information from the different images.
  • computational efficiency was maximised by predefining vectors and matrices of the correct size, as well as optimising long mathematical expressions by splitting them into small reusable blocks.
  • the user inputs the resolution of the images and the coordinates of the tie-points.
  • the program then calculates, for each image, initial guesses for the three unknown mapping parameters, ⁇ c , ⁇ ⁇ d, in order to prime Newton's method with reasonable initial guesses and enable the correct roots to be obtained by taking the means of the two tie-point azimuth angles and the two tie-point inclination angles, respectively.
  • the initial guess for dvs> calculated using the approximate equation.
  • ⁇ * is the approximate horizontal field of view of the lens after rectification. This equation cannot be used to determine ⁇ analytically since ⁇ a varies as the camera is focused.
  • the tool for saving the output file is save.m.
  • This function creates a .txt output file with a filename of the user's choice.
  • the file is saved in the following format:
  • the point cloud data is now suitably coloured and can be imported into appropriate visualisation software, such as the open-source program Para View.
  • mapping procedure can be carried out without re-solving for the mapping parameters, using ma ⁇ _excl_solve.m.
  • This function is the same as map.m, except that it uses whatever values of the mapping parameters are stored in Matlab's workspace. The user is, therefore, able to adjust the mapping iteratively to improve the accuracy of the registration if the tie-points were difficult to determine accurately.
  • the values of the mapping parameters can be written to a .txt file at any time using the function save_ ⁇ arameters.m.
  • Cloud_convert.m is a useful tool for converting a point from Cartesian to spherical polar coordinates using expressions (vii) and (vui).
  • tie points and the equations above sets out one way in which the relationship between the horizontal and vertical pixels and laser points can be established.
  • the computer software is working backwards from the tie points to arrive at the angle at which the camera was pointing with respect to the zero angle when the picture was taken.
  • these angles may be measured electronically by including potentiometers in the mounting arrangement which measure the angles through which the camera has been panned horizontally and tilted vertically.
  • An electronic output from the potentiometer is proportional to the angle through which the camera has been panned.
  • the output could be recorded on each occasion that a picture is taken and subsequently used in the software.
  • Another option would be to equip the mount with scales to measure the azimuth and inclination angles of the camera with respect to the zero angle when any picture is taken. The angles could be recorded manually following the operator reading off the angles from the scale.
  • the points in the point cloud are meshed together.
  • the resulting surface is a mesh of triangles formed between points in the point cloud.
  • colour information relating to respective triangles is applied to the mesh. This can provide a more detailed colour representation, as every pixel is applied to the surface of the mesh (except where photographs overlap), whereas without the creation of a mesh only the pixel closest to each point is used to colour the point cloud.

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • General Engineering & Computer Science (AREA)
  • General Physics & Mathematics (AREA)
  • Mechanical Engineering (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Remote Sensing (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Electromagnetism (AREA)
  • Multimedia (AREA)
  • Studio Devices (AREA)

Abstract

L'invention concerne un dispositif de montage de caméra approprié pour une utilisation dans un dispositif à balayage laser terrestre de couleur naturelle, lequel dispositif comprend un support pour une fixation à une structure de support et un élément de montage de caméra. Le dispositif assure que la position de la caméra soit fixe par rapport au support dans trois plans orthogonaux et soit sélectivement ajustée dans au moins deux de ces plans, afin que le centre optique de la caméra coïncide avec le centre optique d'un détecteur de faisceau laser d'un dispositif à balayage laser terrestre pouvant être monté sur la structure de support. Le dispositif assure en outre la rotation de la caméra dans deux plans orthogonaux.
PCT/GB2008/050157 2007-03-05 2008-03-05 Imagerie laser améliorée en couleur WO2008107720A1 (fr)

Applications Claiming Priority (2)

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GB0704165.0 2007-03-05
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