JP4052382B2 - Non-contact image measuring device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a non-contact image measuring apparatus capable of practically implementing simple digital photogrammetry using a high-resolution digital camera for consumer use.
[0002]
[Prior art]
The change from analog to digital in photogrammetry is the transition from film to CCD (electrically coupled device) sensor, eliminating the time loss that was unavoidable with conventional film cameras such as film development and printing, and real-time Image acquisition is now possible. Recently, with the rapid development of sensor technology, the resolution of CCD sensors has been increasing rapidly, and a wide variety of high-resolution consumer digital cameras have been released. Simple digital photogrammetry using high-resolution consumer digital cameras Is expected in many fields.
[0003]
Conventionally, as a technique for associating distance with a photographed image, a grayscale image for a wide range of real space is acquired, distance information from a camera is acquired for an arbitrary point in the image, and the images are connected. A technology of an image creation apparatus with distance information in which a panorama image is created and distance information of an object whose distance is measured is recorded in the panorama image is disclosed (Patent Document 1).
On the other hand, in photogrammetry that deals with obtaining the spatial position of an object, that is, obtaining three-dimensional coordinates, there are various types such as ground photogrammetry and aerial photogrammetry, but the principle that is based on them is the same. It is a projected image. More specifically, photogrammetry measures the plane coordinates of a photograph, which is a central projection image, and further uses the geometrical condition of light that connects the subject, lens, and film (or image sensor), that is, the spatial position of the subject, It is to obtain three-dimensional coordinates. Some errors are always included in the measurement, and for the photo side quantity, the optimum value of the unknown variable must be obtained from the measurement values including various errors, and correction of lens distortion, focal length, principal point position, etc. Internal orientation based on the internal orientation elements of the parameters and external orientation based on the external orientation elements of the position of the photographing point and the camera tilt are considered to be important (Non-Patent Document 1).
[0004]
[Patent Document 1]
JP-A-2000-227963 [Non-Patent Document 1]
Published by the Japan Photogrammetry Society (revised in April 1997), published by the Analytical Photogrammetry Committee "Analytical Photogrammetry"
[0005]
[Problems to be solved by the invention]
From the above background, the inventor has studied the application of high-resolution consumer digital cameras to digital photogrammetry, and has further developed software for digital photogrammetry using consumer digital cameras.
[0006]
However, in many of the current methods, the internal orientation elements need to be acquired in advance, and in order to acquire the actual coordinates for the target object, a scale distance or an altitude reference point is required in the target space. This is a bottleneck in putting simple digital photogrammetry with a consumer digital camera into practical use.
[0007]
In Patent Document 1, distance information is simply associated with identification of a captured image. When a panoramic image is created by connecting 10 images, distance information for 10 points is recorded in the image. Will be. In Patent Document 1, as described on the sixth page, a projective transformation formula is used for superimposing images, but this transformation formula is strictly called a two-dimensional projective transformation formula, Is limited to a plane. Therefore, there is an error in converting to a real space having three-dimensional coordinates by this equation, and this error can be a large error that cannot be overlooked in the field of photogrammetry. On the other hand, in the field of photogrammetry, accurate three-dimensional coordinates in real space are required rather than being expressed on a computer monitor, and the level required for accuracy is completely different.
[0008]
The present invention has been made to solve the above-described conventional problems, and enables on-site calibration that eliminates the need for a scaled distance or an altitude reference point constraint and a ground reference point in the target space. Thus, an object of the present invention is to provide a non-contact image measurement device that enables high-precision photogrammetry in a target space under conditions where a reference point cannot be placed in the target space.
[0009]
[Means for Solving the Problems]
That is, the present invention has the following configuration in order to solve the above problems.
The present invention comprises a digital imaging means for photographing a measurement target space including six or more pseudo reference points from two or more photographing locations ;
Image coordinate calculation means for obtaining image coordinates of each pseudo reference point in the image photographed by the digital imaging means ;
A laser rangefinder that measures the distance from the above-mentioned two or more photographing locations to each pseudo reference point in the measurement target space in a non-contact manner;
Optical axis coincidence for causing the photographing optical axis of the digital imaging means and the laser optical axis of the laser distance meter to coincide with each other so that the photographing optical axis and the laser optical axis are directed to the pseudo reference point in the measurement target space . Means,
Based on the obtained image coordinates and measurement distances for six or more pseudo reference points in the measurement target space taken from two or more photographing locations and measured for distance, external orientation elements and internal orientation elements of the digital imaging means are calculated. Computing means for
A storage means for storing and storing a captured image of the digital imaging means, a measurement distance, an image coordinate external orientation element, and an internal orientation element;
External orientation elements of the digital imaging means for storing stored in the storage means, and based on the internal orientation parameters, characterized in that allowed the precise three-dimensional measurement of the object space by performing the on-site calibration of the digital imaging means non It is a contact image measuring device.
Here, in order to perform photogrammetry accurately, it is necessary to correctly know the distance from the center of the digital imaging means to the measurement point on the measurement target space.
Therefore, the camera and the laser distance meter are not set so that the optical axes of the laser and the camera are parallel to each other as in the conventional patent document 1, and the present invention uses an optical axis matching means such as a half mirror. The optical axis of the digital imaging means and the optical axis of the laser distance meter are made to completely coincide.
Further, in the present invention, photographing is performed from two or more positions, distance measurement is performed, and six or more measurement points in the measurement target space (preferably, for example, easy to recognize on the monitor image) by the digital imaging unit, laser distance meter, and coordinate calculation unit. In the present invention , the measurement point is an image coordinate obtained with respect to a pseudo reference point, that is, referred to as a “pseudo reference point”. ) And external orientation elements and internal orientation elements can be calculated based on the distance measured by the laser rangefinder , and digital imaging means can be calibrated based on the calculated external orientation elements and internal orientation elements . become.
Therefore, even if a reference point is not separately provided in the measurement target space, the pseudo reference point can be appropriately set in the measurement target space. Therefore, natural terrain and buildings that could not be measured because a reference point could not be provided in the past. Can be easily and accurately performed. In other words, the inventor has developed an image measurement system in which a 3 million pixel digital camera for consumer use, a laser distance meter, and a personal computer are integrated, and a scale distance or altitude reference point constraint condition and ground reference point in the target space. Enables on-site calibration that eliminates the need for
Therefore , it is possible to construct a system that can perform precise three-dimensional measurement of the target space and further three-dimensional representation on site and on site.
[0010]
The optical axis matching means is a half mirror provided on the optical axis between the measurement target space and the digital imaging means, and transmits the half mirror to the measurement target space of the digital imaging means. It is preferable to have the half mirror for matching the optical axis toward the measurement point with the laser optical axis reflected by the half mirror and toward the measurement point in the measurement target space. Thereby, it is possible to optically accurately match both optical axes of the digital imaging means and the laser distance meter with a simple structure called a half mirror.
Also, monitor means for displaying an image captured by the digital imaging means (for example, as a finder image) on a screen and displaying a laser beam irradiation point of the laser distance meter on the display screen, optical axes of the digital imaging means and the laser distance meter It is preferable that at least one of the optical axes is adjusted. When performing photogrammetry in a non-contact image measuring device, the optical axis is adjusted in advance and then brought to the surveying site. It is desirable that the optical axis can be adjusted again at the site. As a result, a real-time image is acquired, calibration at the imaging site (on-site calibration) and a real-time image are acquired, and three-dimensional measurement (3D measurement) of the target space becomes possible.
In addition, the digital image pickup means, laser distance meter, storage means, half mirror, monitor means, optical axis adjustment means, and data processing means are provided in an integrated case, and the case is rotated biaxially in the turning direction and the elevation direction. It is preferable to provide support means for pivotally supporting (providing a dedicated tripod or the like that is not capable of biaxial rotation). In this way, it is possible to measure the oblique distance from the digital image pickup means to the measurement point in the measurement target space, and the digital image pickup means, the laser distance meter, the monitor means, etc. are housed in an integrated housing. By acquiring the image, it is possible to acquire an image in real time, and to perform on-site calibration and 3D measurement more easily and accurately. In the non-contact image measuring device of the present invention, the subject space is photographed and the distance is measured from two positions. Further, it is possible to perform surveying while looking at the monitor while keeping the optical axes of the digital imaging means and the laser distance meter in agreement. Therefore, handling of the non-contact image measuring apparatus itself is easy and surveying accuracy is improved.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is an explanatory block diagram of a non-contact image measuring apparatus according to an embodiment.
As shown in FIG. 1, the non-contact measuring device captures a measurement target space including a measurement point, and has a digital camera (digital imaging means) 10 having a zoom function and image coordinates of the measurement point in the captured image. The coordinate calculation means 12 such as the personal computer 22 to be obtained below, the laser distance meter 14 that measures the distance to the measurement point in the measurement target space in a non-contact manner, the imaging optical axis 16 of the digital camera 10 and the laser distance meter 14 A half mirror (optical axis matching means) 20 for causing the laser optical axis 18 to coincide with each other toward the measurement point in the measurement object space, the digital camera 10 from two or more positions, and a laser distance meter 14 An external orientation element of the digital camera 10 based on the obtained image coordinates and measurement distances for six or more measurement points in the measurement target space whose distance is measured. A personal computer to calculate the internal orientation parameters and: have (PC example of an arithmetic unit) 22, and makes it possible to three-dimensional measurement of the measurement object space.
[0012]
The non-contact image measuring device stores and stores a photographed image of the digital camera 10, a measurement distance of the laser rangefinder 14, a calculated image coordinate, a calculated external orientation element, an internal orientation element, and the like. 24, a monitor (monitor means) 26 comprising a liquid crystal display element for displaying an image photographed by the digital camera 10 on a screen and displaying a laser light irradiation point of the laser distance meter 14 on the display screen, the digital camera 10 and And an optical axis adjusting means including a rotatable mirror 32 that enables adjustment of at least one of the optical axes of the laser rangefinder 14.
[0013]
The half mirror 20 as the optical axis matching means is a half mirror 20 provided on the optical axis 16 of the digital camera 10 facing the measurement target space, and the half mirror 20 (front surface 20f, back surface 20r). And the laser beam emitted from the laser distance meter 14 is reflected by the surface 20f of the half mirror 20 and is reflected by the surface 20f of the half mirror 20. This is a half mirror 20 for matching the laser optical axis 18 toward the measurement point.
[0014]
The non-contact image measuring apparatus according to the embodiment includes a digital camera 10, a laser distance meter 14, a memory 24, a half mirror 20, a monitor 26, a mirror 32 as an optical axis adjusting unit, and a calculating unit 22 in an integrated housing 28. At the same time, the housing 28 is pivotally supported so as to be biaxially rotatable in a turning direction (turning direction axis 30A) on the horizontal plane and an elevation angle direction (elevation angle direction axis 30B) in the vertical direction (a tripod capable of biaxial rotation is used). ) A support structure 30 is provided.
Note that the laser emission direction of the laser distance meter 14 itself provided in the housing 28 is parallel to the photographing optical axis of the digital camera 10, but is totally reflected in front of the laser emission of the laser distance meter 14. A mirror 32 is provided so as to be rotatable about the shaft, and the laser beam 14A emitted from the laser distance meter is reflected by the mirror 32 to guide the laser beam 14A to the surface 20f of the half mirror 20. The angle position of the mirror 32 can be adjusted and the optical axis 18 of the laser light 14A can be adjusted to make the laser optical axis 18 and the photographing optical axis 16 coincide.
[0015]
The personal computer 22 for data processing for displaying an image on the monitor 26 includes a hard disk drive (HDD) 24A and a random access memory (RAM) 24B as a memory (storage means) 24, and an arithmetic processing means. The central processing unit (CPU) 22A is provided on the motherboard 22B and is accommodated in the housing 28.
Specifically, the digital camera is 3.14 million pixels, the laser rangefinder 12 is ± 3 mm up to a distance accuracy of 40 m, and a video capture board 22C is connected to the motherboard 22B for transferring a finder image.
[0016]
A method for obtaining the external orientation element and the internal orientation element in the non-contact image measurement apparatus according to the embodiment will be described.
When measuring an image, it is necessary to correctly know the distance from the center of the digital camera to the target space. Therefore, the half mirror 20 is set so that the laser optical axis 18 and the digital camera 10 optical axis (photographing optical axis) 16 completely coincide with each other. Used. The monitor 26 can also be used as a viewfinder of the digital camera 10.
[1] First, the image of the measurement target space by the digital camera 10 is taken into the personal computer 22 from the first position where the measurement target space can be seen.
[2] Then, with respect to six feature points (pseudo reference points) in the measurement target space, the housing 28 containing the system of the non-contact image measuring device is rotated on the support structure 30 and the laser distance meter for that point. 14 to measure the distance.
[3] A measurement point can be aimed through the monitor (finder) 26, and the point irradiated with the laser light 14A can be accurately matched with the measurement point by using the zoom function of the digital camera 10. Further, in order to prevent an error associated with the rotation of the system, the rotation center of the system and the center of the camera axis are made to coincide.
[4] The image coordinates of the measurement point can be obtained by image processing by the personal computer 22 or can be obtained manually. Further, these obtained image coordinates are recorded in the memory 24 of the personal computer 22 in association with the distance.
[5] Then, after obtaining image coordinates and distances for six or more measurement points (feature points), the personal computer 22 calculates a digital camera calibration (external orientation elements and internal orientation elements of the digital camera). .
[6] The system of the non-contact image measuring device such as the digital camera 10 is moved from the first position and installed at the second position, and the operations from [1] to [5] are performed.
[7] From now on, as in conventional photogrammetry, three-dimensional coordinates of the measurement target space are calculated by the bundle adjustment method for stereo images taken and measured at two positions, and the existing CG software (computer graphics) 3D representation using software.
[0017]
Next, calculation of the calibration of the digital camera (external orientation elements and internal orientation elements of the digital camera) will be described.
The non-contact image measurement apparatus of the present embodiment enables an on-site calibration method (calibration at the measurement site) that does not require the installation of a ground reference point, and is obtained by the non-contact image measurement apparatus. The left and right stereo images obtained at two positions are simultaneously adjusted with the distance as a constraint, and the left and right camera position three-dimensional coordinates (X0L, Y0L, Z0L), (X0R, Y0R, Z0R), left and right camera postures (ΩL, ψL, κL), (ωR, ψR, κR), camera focal length f, principal point positions x0, y0, distortion count p1, sensor-to-screen conversion coefficients a1, a2, and pseudo reference point 3 Dimensional coordinates are unknown. The pseudo reference point is a point in the measurement target space where a distance used for calibration (calibration) is measured. For on-site calibration, six or more points are included in the measurement target space. A pseudo reference point is necessary. In this case, 36 conditional expressions are obtained for 30 unknown quantities.
[0018]
explain in detail. In the above case, in image acquisition, six external orientation elements (photographing point position and camera tilt) are unknown amounts. Since the image is taken from two places, twelve external orientation elements for the left and right cameras are unknown. Further, six of the internal orientation elements (main point positions x0, y0, focal length f, affine transformation coefficients a1, a2, and lens distortion coefficient p1) are unknown quantities. Although it is slightly different, we will assume that these values do not change this time. Accordingly, 18 left and right external orientation elements and internal orientation elements in total are unknown quantities.
[0019]
Next, distance measurement is performed on six pseudo reference points in the measurement target space. Since the three-dimensional coordinates with respect to the pseudo reference point are also unknown quantities, 6 × 3 = 18 are unknown quantities. Thus, a total of 36 unknown quantities are obtained.
On the other hand, since two collinear conditional expressions are obtained for one pseudo reference point, twelve of the six pseudo reference points from one photograph are solved simultaneously for the left and right images. Thus, a total of 24 conditional expressions are obtained.
[0020]
Furthermore, since distance measurement is performed for the same pseudo reference turning point in the target space at the left and right camera positions, one distance conditional expression (distance constraint expression) for one pseudo reference turning point. 6 distance conditional expressions can be made with one image, and 6 + 6 = 12 distance conditional expressions can be made by simultaneously handling the left and right images.
Therefore, the number of conditional expressions is 24 + 12 = 36, where the number of unknowns and the number of equations are equal, and the problem can be solved.
[0021]
In the above case, the unknown quantity is 30. In order to reduce the number of unknown quantities, for example, one point in the pseudo reference point is assumed to be the origin (0, 0, 0). Then, since the three-dimensional coordinate with respect to the pseudo reference point is known, it is reduced by 3 from the unknown amount to 33. In addition, if the X axis and the Y axis are determined in the measurement target space, three unknown quantities can be further reduced geometrically, and finally 30 unknown quantities are obtained.
Usually 30 unknowns can be solved if there are 30 equations, but in this case, nonlinear equations will be handled, so usually the number of unknowns is less than the conditional expression, Solve by the least squares method. Although the non-contact measurement is enabled by including the distance condition, the point of the solution is that the left and right cameras, that is, the images from two places are handled at the same time.
[0022]
The inventor performed stereo imaging of the test target T as shown in FIG. 3 in order to verify the application of the non-contact image measuring apparatus embodying the present invention to image sensing. The test target T was provided with 42 circular black circle D targets, and the accuracy of the three-dimensional coordinates with respect to the measured 42 black circles D (side points) was verified. The test target T has a length of 1.8 m, a width of 1.55 m, a depth Z (center two rows) of 0.33 m, and is provided with seven vertical and six horizontal black circles D at equal intervals. In addition, a reflective sticker E is attached to the center of each black circle D, and the measurement result using a first-class total station (distance accuracy ± 1 mm, angular accuracy ± 2 ″) is shown in the center of this reflective seal E. True value.
The image coordinates of each test target T are obtained as a center of gravity of the center of the black circle by binarizing the captured image to extract only the black circle D portion.
The shooting situation in stereo shooting is shown in FIG.
[0023]
On the other hand, FIG. 5 shows the results obtained by performing the on-site calibration by the non-contact image measuring apparatus embodying the present invention and obtaining the mean square error (RMSE1) with respect to the 42 side points (black circles), and the reference FIG. 9 shows the result of calculating the mean square error (RMSE2) for 33 side points by performing camera calibration by using the conventional bundle adjustment method using 9 points. FIG.
From FIG. 5, the result of the non-contact image measurement apparatus according to the present invention is slightly lower than the result of the bundle adjustment method using the conventional reference point in both the plane and depth accuracy. The reason for this is that the result of the non-contact image measuring device is presumed to be the accuracy of the measurement distance and the incompleteness of the coincidence between the optical axis and the laser axis. Considering that ground-based reference point installation work that required labor and time is not necessary, that on-site 3D (three-dimensional) measurement is possible, and that on-site modeling is also possible, It can be understood that this is a very effective method in the field of image sensing using a digital camera.
[0024]
【The invention's effect】
As described above, according to the present invention, it is possible to perform on-site calibration that eliminates the need for a scaled distance or an altitude reference point constraint condition and a ground reference point in the target space, and places the reference point in the target space. High-precision photogrammetry can be performed in the target space with no conditions
In the present invention, monitor means for displaying a photographed image and a photographing optical axis by the digital imaging means and displaying a laser light irradiation point of the laser distance meter on the display image, and adjusting at least the optical axis of the laser distance meter If the optical axis adjusting means is provided, the imaging optical axis and the laser beam irradiation point of the laser distance meter can be displayed on the monitor means. The optical axis can be adjusted, and real-time images can be acquired to obtain on-site calibration (on-site calibration) and real-time images, and 3D measurement (3D measurement) of the countermeasures is possible. become.
Further, it has data processing means for storing captured image data and distance data in the memory means and displaying the image on the monitor means, and includes a digital imaging means, a laser distance meter, a memory means, a half mirror, a monitor means, and an optical axis adjusting means. In addition, the data processing means is provided in an integral casing, and supporting means (using a dedicated tripod capable of two-axis rotation, etc.) that supports the two-axis rotation in the turning direction and the elevation angle direction is provided. In this way, the oblique distance from the digital imaging means to the measurement point in the measurement target space can be measured, and the digital imaging means, the laser distance meter, the monitor means, etc. are accommodated in an integrated housing. Integrated into a real-time image acquisition via a data processing means such as a video capture board. And possible 3D measurement even more easily and accurately.
[Brief description of the drawings]
FIG. 1 is an explanatory block diagram of a non-contact image measuring apparatus according to an embodiment of the present invention.
FIG. 2 is an explanatory diagram of attachment of the non-contact image measuring device of FIG. 1 to a support portion.
FIGS. 3A and 3B are external explanatory views of a test target for verifying the non-contact image measuring apparatus according to the present invention, where FIG. 3A is an overall view of the test target, and FIG. 3B is an explanatory view of each target (black circle); It is.
FIG. 4 is also an explanatory diagram of a shooting situation for verifying the non-contact image measuring apparatus according to the present invention.
FIG. 5 shows a result of on-site calibration performed by a non-contact image measuring apparatus embodying the present invention and a result of camera calibration performed by a conventional bundle adjustment method.
[Explanation of symbols]
10 Digital video camera (digital imaging means)
12 Coordinate operation means 14 Laser distance meter 16 Imaging optical axis 18 Laser optical axis 20 Half mirror (optical axis matching means)
22 Personal computer (calculation means)
22A Central processing unit (CPU)
22B Motherboard 24 Memory (memory means)
24A hard disk drive (HDD)
24B random access memory (RAM)
26 Memory 28 Housing 30 Support structure 30A Rotation direction axis 30B Elevation angle axis 32 Mirror D Test target (black circle)
T test target

Claims (4)

Digital imaging means for photographing a measurement target space including six or more pseudo reference points from two or more photographing locations ;
Image coordinate calculation means for obtaining image coordinates of each pseudo reference point in the image photographed by the digital imaging means ;
A laser rangefinder for measuring the distance to each pseudo reference point of the measurement object in space without contact from the 2 position or photographing locations,
Optical axis coincidence for causing the photographing optical axis of the digital imaging means and the laser optical axis of the laser distance meter to coincide with each other so that the photographing optical axis and the laser optical axis are directed to the pseudo reference point in the measurement target space . Means,
Based on the obtained image coordinates and measurement distances for six or more pseudo reference points in the measurement target space taken from two or more photographing locations and measured for distance, external orientation elements and internal orientation elements of the digital imaging means are calculated. Computing means for
A storage means for storing and storing a captured image of the digital imaging means, a measurement distance, an image coordinate external orientation element, and an internal orientation element;
External orientation elements of the digital imaging means for storing stored in the storage means, and based on the internal orientation parameters, characterized in that allowed the precise three-dimensional measurement of the object space by performing the on-site calibration of the digital imaging means non Contact image measurement device.   The optical axis matching means is a half mirror provided on the optical axis between the measurement target space and the digital imaging means, and passes through the half mirror to the measurement point of the measurement target space of the digital imaging means. 2. The non-contact image measuring apparatus according to claim 1, further comprising: the half mirror configured to match an optical axis toward the laser optical axis reflected by the half mirror toward the measurement point in the measurement target space. Monitor means for displaying a photographed image by the digital imaging means on a screen and displaying a laser light irradiation point of a laser distance meter on the display screen;
The non-contact image measuring apparatus according to claim 1, further comprising an optical axis adjusting unit that enables adjustment of at least one of the optical axes of the digital imaging unit and the laser distance meter.   The digital imaging means, laser distance meter, storage means, half mirror, monitor means, optical axis adjustment means, and data processing means are provided in an integrated housing, and the housing can be rotated in two axes in the turning direction and the elevation angle direction. The non-contact image measuring apparatus according to claim 1, further comprising a supporting unit that supports the shaft.

Images