CN1412537A - Method for Finding Camera Optical Projection Parameters - Google Patents

Abstract

The present invention is a method for calculating the optical projection parameters of a camera, which utilizes the center-symmetric characteristic of the distorted image, and determines the optical axis of the camera lens by means of a correction object having a plurality of symmetrical and concentric geometric figures, and then Find out its projection center point by trial and error on the optical axis, and simultaneously find out its equivalent focal length and classify its original projection mode; because the present invention can determine the internal and external parameters of the camera exactly, and correct The method is simple, low-cost, applicable to any projection mode, and the greater the image distortion, the better the sensitivity. Therefore, the distorted image can be easily converted into a normal image that conforms to the center projection mechanism, and it can be applied to identify fish Spectacle lens characteristics and the field of stereoscopic image positioning.

Description

Method for Finding Camera Optical Projection Parameters

technical field

The present invention relates to a method for digital image processing and presentation, and in particular to a method for recovering distorted images by finding optical projection parameters such as the projection center (viewpoint) and equivalent focal length (focal length) of the camera lens. Method for normal perspective images.

Background technique

Usually the general optical lens is used for imaging, and most of them hope that it conforms to the imaging result of linear projection. The image captured by the user under a similar lens will be very close to the real world, but it has a shortcoming—the angle of view is small, and the standard lens is used as the For example, the angle of view is about 45 degrees to 55 degrees. Therefore, in fields that require a large angle of view, such as monitors or endoscopes, wide-angle lenses or fisheye lenses are used instead, so that images with a large angle of view can be captured at one time. .

Among them, the fisheye lens is used to capture very wide-angle images. Usually, a camera equipped with a fisheye lens can capture a field of view of 180 degrees or even more, and only needs to capture an image once, without moving the camera itself for multiple shots, but with the angle of view The original image also has serious distortion problems, so image correction technology is usually required to output a perspective image that is closer to the real world. The accuracy of image correction affects the range that the fisheye lens can be applied to; for a general surveillance system, if it is only required to be able to see the movement of people or objects within the surveillance range, then partial distortion of the picture can also be tolerated If it is to take pictures of virtual reality (Virtual Reality), as long as the image "looks" normal and clear; but if it is to be applied to the field of image positioning, such as endoscopy or robot vision, at present Under the condition that many optical parameters of the fisheye lens are unknown, it is difficult to accurately determine the real position of the image in space.

In any case, for consumers, if the lens can have a large viewing angle, accurate and clear images, and precise positioning, it will be the most competitive in the market. Moreover, the fisheye lens has the advantage of infinite depth of field, which is unmatched by other types of lenses. Therefore, how to correct the image produced by the fisheye lens is an important issue.

In the prior art, there are many methods for correcting distorted images. R.Y.Tsai (1987) used five known non-coplanar points in space and the operation of a rotation matrix and a transformation matrix to obtain the projection center (viewpoint) and focal length (focal length) of the lens. The results calculated by the simulation are quite accurate, but because the theoretical derivation is based on linear projection, when it is applied to a severe nonlinear projection mechanism such as a fisheye lens, the error in calculating the equivalent focal length is quite large, so it cannot be directly Continue to use and become a common correction method. Afterwards, a simple correction method for fisheye lens appears, please refer to Figure 1A and Figure 1B, where Figure 1B is the hemispherical space projection mode corresponding to Figure 1A, assuming that the image plane 1 is elliptical (or circular) Next, the intersection point 13 of its long axis 11 and short axis 12 is just the center of the image (point C in the figure). In addition, it is also believed that the field of view captured by the fisheye lens is exactly 180 degrees. Based on the above-mentioned several premises, it is inferred that the image The incident azimuth angle (zenithal angle) at the edge of plane 1 is π/2, the azimuth angle of the center point 13 is 0, and the azimuth angle θ of the rest points is individually estimated according to their relative positions with point C 13 and the edge. For example, point A in Figure 1A should correspond to point A in Figure 1B. The above-mentioned method of calibrating the fisheye lens image is simple and does not require the assistance of an additional calibration target. This is the camera description mode used by many fisheye cameras that directly calibrate planar images. However, its assumptions are quite uncertain. First of all, the distortion center point 13 of the picture may not be exactly the actual center point of the image, and the edges of the fisheye lens image are blurred, so it is difficult to determine the so-called 180-degree boundary; the most important The problem is that the radius and center of the hemisphere cannot be located, and it is difficult to evaluate the fidelity of the corrected image in this image-based analysis mode. Obviously, such a correction method is not suitable for the field of stereo image positioning.

In terms of patent disclosure, TeleRobotic International Inc. proposed several patents on fisheye lens cameras (US Patent No. 5185667, 5313306, 5359363, 5384588). Generally speaking, the technical content is based on the aforementioned camera mode, using a fish The spectacle lens shoots the entire hemispherical field of view, and then uses a computer to control a specially designed electronic circuit to digitally convert the original distorted image into a normal perspective image and display it on the fluorescent screen. This technology is applied in the whole world Position display, surveillance, endoscope and remote control, etc. Later, Interactive Pictures Corporation proposed a series of improved new solutions based on the aforementioned TeleRobotic International Inc. technology (US Patent No. 5764276, 5877801, 5903319, 5990941, 6002430, 6147709, 6201574B1). However, no matter which of the above-mentioned technical contents, they all use a fixed projection mode to correct the image, and have not exactly determined the parameters of the fisheye lens camera - the projection center (viewpoint) and the focal length (focal length). For the projection mode It is also assumed that the projection mode described in FIG. 1A and FIG. 1B - "Equidistant Projection" - the most common fisheye lens projection mode. In the situation where the precise parameters are not determined and the projection mode is not clear, the original image can only be unfolded and restored, and the accuracy of the corrected image cannot be considered. The application in the field of stereoscopic image positioning is bound to be limited.

In fact, currently known fisheye lens projection modes, in addition to "Equidistant Projection", also include "Stereographic Projection" and "Orthographic Projection". The mathematical relations are expressed as follows:

1. Equidistant projection: IH=fθ

2. Stereoscopic image projection: IH=2f×tan(θ/2)

3. Right-angle projection: IH=f×sinθ

in,

IH: the distance between the image point and the optical axis of the lens (image height);

f: equivalent focal length of the fisheye lens;

θ: The incident angle of the object point to the focal plane, that is, the angle between the incident light and the optical axis.

Theoretically, "stereoscopic image projection" is the best fisheye lens projection mode; but due to optical design reasons, the fisheye lens that conforms to the "equidistant projection" theory is the easiest to manufacture, which also makes the currently known There is a hypothesis in the correction technology: the projection mode of all fisheye lenses is "equidistant projection", but in fact it is not necessary.

On the other hand, although the lens is manufactured according to a certain design, it is difficult to verify whether it is still the original design specification after the manufacture is completed; in addition, after the fisheye lens is assembled into a real system (such as a camera), Its effective focal length and observable angle of view are more likely to change accordingly. Therefore, if there is a simple and universal technology that can test the specifications of fisheye lenses or their image capture devices, so that they have more definite specifications when they are shipped, then It can greatly increase the added value of the fisheye lens.

For fisheye lenses, those of ordinary skill in the art believe that there is no "actual" projection center, which is from the point of view of rectilinear projection. If the corresponding projection mode can be summarized and the optical projection parameters such as the projection center and equivalent focal length can be found, not only can the correct projected image be easily corrected, it can be applied to the field of stereoscopic image positioning, and it can also be applied to product quality management. .

Contents of the invention

In view of this, the object of the present invention is to provide an essential solution based on the identification of the original optical projection mode of the lens for the image correction problem of the severe nonlinear projection mechanism.

Another object of the present invention is to determine the projection center and effective focal length of the camera, so that the image can be corrected more accurately and applied in the field of stereoscopic image stabilization. Another object of the present invention is to provide a method for inspecting the spatial projection mechanism of the fisheye lens or its imaging device, so as to make product specifications or quality control before shipment.

According to the purpose of the present invention above, a method for calculating optical projection parameters of a camera is provided. First, place a calibration object in the form of a plane with a test pattern in the field of view of the fisheye camera, adjust the direction and position of the calibration object so that the corresponding image formed by it is also a similar geometric pattern, and then connect the test pattern and the corresponding image center of the fisheye lens, the optical axis of the fisheye lens can be determined; after that, a certain point is found along the optical axis by trial and error, so that the corresponding image height of the test pattern and the direction angle (zenithal angle), conform to a projection mode (projection mode).

The above-mentioned projection mode may be one of currently known fisheye lens projection modes such as "Equidistant Projection", "Stereographic Projection" or "Orthographic Projection". The fixed point found is the projection center (viewpoint) of the fisheye camera, and its equivalent focal length can be obtained from the mathematical relationship of its projection mode.

Because the present invention can accurately determine the projection center and equivalent focal length of the fisheye lens camera, and can find its original projection mode, it can easily correct the distorted image and find out the projection curve of its view space.

In order to make the above and other objects, features, and advantages of the present invention more comprehensible, a preferred embodiment will be described in detail below together with the accompanying drawings.

Description of drawings

FIG. 1A and FIG. 1B show a known fisheye lens image correction method based on a planar image and a schematic diagram of its spatial projection conversion;

Fig. 2 shows the optical path schematic diagram of determining the optical axis of the fisheye lens in the present invention;

Figures 3A to 3D represent four embodiments of the test pattern on the calibration object in the present invention;

Fig. 4 shows the optical path schematic diagram of finding the projection center and the equivalent focal length by taking the "equidistant projection" mode as an example in the present invention;

Fig. 5 shows the asymptotic graph of obtaining projection center when the present invention is actually tested; and

FIG. 6 shows an embodiment of the correction object of the present invention that addresses viewing angles greater than 180 degrees.

Detailed ways

Although the image projected by a lens with axisymmetric nonlinear distortion such as a fisheye lens has serious distortion problems, its distortion phenomenon has the following characteristics: its image is center-symmetric on the focal plane, and this center point is called distortion Center, the optical projection light path in space is symmetrical to its optical axis, which is a phenomenon well known to those skilled in the art. The present invention first uses this phenomenon to determine the optical axis of the fisheye lens, and then uses the optical axis The axis is used as a reference to find the projection center of the fisheye lens camera, and its focal length can be calculated and its projection mode can be summarized.

Please refer to Fig. 2, a calibration object (calibration target) 22 must be utilized in order to realize the method of the present invention, and there must be at least one geometric figure on the calibration object 22, if there are multiple geometric figures, they must be concentric and symmetrical, such as shown in the figure The concentric circles are called a test pattern (test pattern) 220 . When performing calibration, the calibration object 22 is placed in the field of view of a fisheye lens camera. At this time, the test pattern 220 will form a corresponding image 230 at an image plane 23 behind the fisheye lens 24 . According to the characteristic that the distorted image is centrosymmetric, if the test pattern 220 is parallel to the image plane 23 and the center point is aligned with the optical axis 21 of the fisheye lens 24, then the corresponding image 230 must also be composed of concentric circles like the test pattern 220 , so as long as the position and direction of the calibration object 22 are properly adjusted until the formed corresponding image 230 becomes composed of concentric circular trajectories, the center of the circle connecting the test pattern 220 and the corresponding image 230 is the optical angle of the fisheye lens 24. axis 21.

The test pattern 220 that can be used in the method of the present invention is not limited to the concentric circles shown in FIG. In addition, concentric squares such as Fig. 3B, concentric triangles such as Fig. 3C, or concentric hexagons such as Fig. 3D can also be used, all of which can be applied to the test pattern 220 in the method of the present invention; even a combination of any number of Concentric and symmetrical circles, squares, triangles and polygons are also other feasible embodiments. However, in the actual test, considering the cylindrical distortion of the image 230, in addition to the circle, it is necessary to set the vertices of geometric figures (such as triangles or squares) as featured coordinates for correction The reference point for the process.

Please refer to Fig. 4, after determining the optical axis 21 of the fisheye lens 24, according to the optical theory, it can be known that the projection center of the lens 24 must be located at a certain point on the optical axis 21, and often just within the fisheye lens 24, so Therefore, the present invention tests one by one along the optical axis 21 in the fisheye lens 24 to find out the projection center point of the fisheye lens 24 by trial and error. As for its test method, it also utilizes the test pattern 220 on the calibration object 22. If the "equidistant projection" (Equidistant Projection) mode is taken as an example, assuming that a certain point 241 on the optical axis 21 has been determined as the optical origin, it can be measured The direction angle θi of the line connecting the fixed point 241 to the object point 221 on each concentric circle deviates from the optical axis 21 and the distance IH from the image point 231 corresponding to the object point 221 to the optical axis 21 (also the center of the image at this time) is measured. _i (or called image height), with these data, f _i can be obtained from the relationship between θ _i under each concentric circle and IH _i . If the camera fully complies with the relational expression of "equidistant projection", then the distortion f _i obtained by computing concentric circles with different radii is a constant.

When the method of the present invention is actually implemented, the test pattern 280 is set as twenty concentric circles, and the distance between each adjacent concentric circle is 5 mm. For the convenience of description, it is assumed that the center point of the calibration object 22 intersects the optical axis 21 at (0, 0, 0), and the optical axis is the z axis, which can be expressed as (0, 0, z). If the projection center and the calibration object 22 is D, and the radius of each concentric circle on the calibration object 22 is set as r _i , which corresponds to each image height IH _i , because IH _i and θ _i are both functions of D, so "equidistant projection" can be changed It is the following type IH _i (D)=fθ _i (D), wherein i=1-20, the outermost circular pattern can be taken as a benchmark, IH ₂₀ (D)=fθ ₂₀ (D), after a simple calculation, it can be get the following equation:

IH _i (D)/IH ₂₀ (D)-θ _i (D)/θ ₂₀ (D)＝0

At this time, if (O, O, D) is changed to an arbitrary point on the z-axis, an error relationship can be obtained as follows:

e _i (z) = IH _i (z)/IH ₂₀ (z)-θ _i (z)/θ ₂₀ (z)

According to the above formula, when the test point is at (O, O, D), e _i (z) is the minimum value, and the distance of the calibration object 22 can be fixed.

However, the above formula only takes two concentric circles. The calculated result is to consider that the test range covers the effective field of view of the camera, and to observe the distortion of the concentric circle imaging along the radial direction, so refer to the coverage of each circular trajectory. , set a weight function w _i (D)=(IH _i (D)−IH _ii (D))/IH ₂₀ (D), where IH ₀ (D)=0, in order to treat the effects of each trajectory fairly. Therefore, in the fitting process of finding the projection center on the optical axis 21 in the present invention, the applied error function is: $\mathrm{\ϵ}\left(z\right)=\underset{i=1}{\overset{20}{\mathrm{\Σ}}}\mathrm{abs}(e_i\left(z\right)\×w_i\left(\mathrm{D.}\right))$

Where z is any point on the optical axis 21, if a unique point can be found to minimize ε(z) or approach 0, then this point is the projection center of the fisheye lens camera. As for the focal length f, based on the measured IH _i (D) and its relative θ _i (D), it is calculated using the following formula: $f\left(\mathrm{D.}\right)=\underset{i=1}{\overset{20}{\mathrm{\Σ}}}{f}_i\left(\mathrm{D.}\right)\×w_i\left(\mathrm{D.}\right)$

Among them, f _i (D)＝IH _i (D)/θ _i (D), if the lens completely conforms to the projection mode, the measurement is error-free and the D value is obtained accurately, then f(D) should be equal to any f _i (D ), which is the focal length f of the lens. In fact, the obtained statistical standard deviation of each f _i (D) can be used to estimate the accuracy of the projection mode, that is to say, the following formula can be used as an indicator of the degree of adaptation to the "equidistant projection" mode : $\mathrm{\σ}\left(\mathrm{D.}\right)=\left(\underset{i=1}{\overset{20}{\mathrm{\Σ}}}{(f_i\left(\mathrm{D.}\right)-f\left(\mathrm{D.}\right))}^2\right)/(20-1)$

Please refer to Figure 5, which shows the asymptotic curve of finding the D value along the z-axis when the BV-7112 camera produced by Opro Corporation is used for testing, and the DW9813 fish of Daiwon Optical (Korea) company is installed in this camera. The spectacle lens, provided by the manufacturer, has a focal length of 1.78mm and a diagonal viewing angle of 170 degrees. In the figure, the first test result is represented by a solid line, and the calibration object 22 is moved outward by 5mm (dD=5), 10mm (dD=10), and 15mm (dD = 15), 20mm (dD = 20) and 25mm (dD = 25) conduct the same test, and found that in the six cases, there is an obvious minimum value of ε (z), which proves that the fisheye The lens does have a projection center, and the present invention can find it out very accurately. The test data related to Figure 5 is shown in Table 1:

Table 1 Test parameters and results D 0 5 10 15 20 25 D. 14.7 19.6 25.2 30 35.3 39.5 f(D) 1.805 1.788 1.827 1.796 1.798 1.784 σ(D) 0.005 0.002 0.0091 0.0058 0.0062 0.0052

(unit: mm)

Observing the data in Table 1, no matter which of the six positions the calibration object 22 is in, the calculated focus drop point (f(D)±σ(D)) is very close, and σ(D) is quite small, It shows that the method of the present invention has quite good accuracy and precision.

After deriving the projection center and focal length of the fisheye camera, image correction becomes very easy. If taking a fisheye camera conforming to the “equidistant projection” mode as an example, please refer to FIG. 4 again. In this projection mode, the mapping relationship between the object point 221 of the hemispherical field of view and the corresponding image point 231 is very direct, and the image can be The plane is represented by a spherical surface 25 whose focal length is the length of the radius. In this way, logically, it can be more like linear projection, the incident light focal plane has the same incidence angle and refraction angle. The length of the projected image of any line of sight can be directly represented by the arc length of its incident angle (that is, the reflection angle). Therefore, when the incident angle is (that is, the reflection angle) θ, its image length is IH=fθ _i , and the image height of the corrected image point 231 ′ is IH′=f×tanθ. It can be clearly seen from Fig. 4 that ΔOPQ is similar to ΔOP'Q', so each corrected IH' is in equal proportion to its corresponding r _i , so the method of the present invention can restore the distorted image very accurately .

Since the method of the present invention will simultaneously check which projection mode of the obtained data makes the error value ε(z) the smallest during the test process, therefore, the method for calculating the projection center and focal length in the present invention is not limited to Applied to the fisheye lens camera in the "equidistance projection" mode, and can also be applied to the "stereoscopic image projection" (IH=2f×tan(θ/2)) or "right-angle projection" (IH=f×sinθ) A camera in the mode, even a nonlinear lens that can identify any known projection function, has the function of inducing and determining the true projection mode of each camera. As for the types of cameras to which the present invention can be applied, there are CCD cameras, CMOS cameras, digital cameras, or a traditional film camera.

It is impossible for the above-mentioned planar calibration object 22 to achieve a viewing angle of 180 degrees. When the viewing angle is 180 degrees, the required calibration object 22 has an infinite radius, but this is often the viewing angle that can be captured by a fisheye lens. As for how to solve this problem, the present invention also provides a solution. Please refer to FIG. 6, as long as the calibration object 22 is extended into a hollow cylinder, it can be achieved, just like an iron can with one end open, and the bottom surface of the can is drawn as before. The described planar form calibrates the object 22 and is used to calibrate the camera orientation and distance. When it has positioned the camera distance D, the optical axis 21 is consistent with the central axis of the circle at this time, and the distance D extends from the surrounding surface 22a around the cylinder to the lens to reach the horizontal line of the fisheye lens camera, as shown in the figure. The object point 222 on the horizontal plane defined by 241 and its corresponding image point 232 are located at the 180-degree boundary of the image. This extension method can be applied to lenses with a field of view greater than 180 degrees.

Since the present invention can accurately determine the projection center and equivalent focal length of the fisheye lens camera, if the orientation of the calibration object 22 is referred to (the orientation of the calibration object 22 is available), multiple groups of cameras can be relatively positioned to form a stereoscopic vision system. And this system will be able to have a larger operable angle of view than ordinary lenses. Using trigonometric calculations to locate the three-dimensional orientation of an object is already familiar to those skilled in the art, so detailed technical content thereof will not be described here. However, the present invention can quickly obtain the focal plane incident angle by the "so-called" distorted image height through the projection formula (because finding the positioned point is necessary for the three-dimensional positioning of the stereo vision system to form the incident angle of the camera group of the stereo vision system steps), which reduces many calculation steps compared with the general method of first correcting the image height conforming to linear projection with a nonlinear high-order function, and then combining the arc tangent function of the linear equivalent focal length to obtain the angle of incidence. Therefore, using the native projection mode to describe a severely nonlinear projection mechanism such as a fisheye lens has an absolute advantage.

The method for locating the fisheye lens camera proposed by the present invention and obtaining its equivalent focal length has the following advantages:

1. The projection center of the fisheye lens camera can be determined exactly and its focal length can be calculated, so the distorted image can be easily restored to the normal image under the center projection mechanism.

2. It is possible to generalize or find out the real projection mode of the fisheye lens camera.

3. It can be applied to the field of stereoscopic image positioning, and has a simpler and faster calculation method of incident angle.

4. The correction method is simple and low-cost, and is applicable to any kind of projection mode fisheye lens or camera with nonlinear projection mechanism.

Although the present invention has been disclosed as above with a preferred embodiment, it is not intended to limit the present invention. Anyone skilled in the art may make some changes and modifications without departing from the spirit and scope of the present invention. , so the scope of protection of the present invention shall prevail as defined by the appended claims.

Claims (21)

1. A method for obtaining camera optical projection parameters, used to obtain the projection center and equivalent focal length of the camera, wherein the applied camera has a lens with axisymmetric nonlinear distortion, and the method includes: providing a calibration object having a test pattern consisting of at least one geometric figure; aligning the center of the test pattern with an optical axis of the lens; and Find a certain point along the optical axis, so that the geometric figure formed on an image plane conforms to a projected model. 2. The method for obtaining camera optical projection parameters according to claim 1, wherein the geometric figure is one selected from the group consisting of circle, square, triangle and polygon. 3. The method for obtaining camera optical projection parameters according to claim 1, characterized in that said geometric figure is composed of multiple concentric circles, concentric squares, concentric triangles or concentric polygons. 4. The method for obtaining camera optical projection parameters according to claim 1, wherein the step of aligning the center of the test pattern with the optical axis of the camera also includes: placing the calibration object in the field of view in front of the camera so that the test pattern forms an image on the image plane; and The position of the calibration object is moved to make the image similar to the test pattern, and the center connecting the test pattern and the image is the optical axis. 5. The method for obtaining camera optical projection parameters according to claim 1, characterized in that said lens with axisymmetric nonlinear distortion is a fisheye lens. 6. The method for obtaining optical projection parameters of a camera according to claim 1, wherein said projection mode is a known nonlinear projection mode. 7. The method for measuring and obtaining optical projection parameters of a camera according to claim 1, wherein the projection mode is one selected from the group consisting of equidistant projection, right angle projection and stereoscopic image projection . 8. The method for measuring and obtaining camera optical projection parameters according to claim 1, characterized in that the fixed point is the projection center of the camera lens, and the image height of the at least one geometric figure and its corresponding incident light and Substituting the included angle of the optical axis into the projection mode for calculation, the equivalent focal length of the camera lens can be obtained. 9. The method for measuring and obtaining optical projection parameters of a camera as claimed in claim 1, wherein said calibration object has at least one plane to provide the test pattern. 10. The method for measuring and obtaining the optical projection parameters of a camera according to claim 9, characterized in that a surrounding surface is vertically extended around the plane, so that the calibration object becomes a hollow tank with one end open shape. 11. The method for measuring and obtaining camera optical projection parameters according to claim 1, characterized in that said camera is selected from a group consisting of a CCD camera, a CMOS camera, a digital camera and a traditional film camera one of them. 12. A method for obtaining the optical projection parameters of a camera, which is used to obtain the optical axis, projection center and equivalent focal length of the camera, wherein the applied camera has an axisymmetric lens with nonlinear distortion, and the method includes: providing a calibration object having a test pattern consisting of at least one geometric figure; placing the calibration object in the field of view in front of the lens so that the test pattern forms a corresponding image on an image plane; moving the position of the calibration object so that the corresponding image is similar to the test pattern, an optical axis connecting the center of the test pattern and the image; and Find a certain point along the optical axis, so that at least one image height corresponding to the geometric figure and the included angle between the incident light of the geometric figure and the optical axis conform to a projection mode. 13. The method for measuring and obtaining the optical projection parameters of a camera according to claim 12, wherein the geometric figure is one selected from a combination of a circle, a square, a triangle and a polygon. 14. The method for measuring and obtaining the optical projection parameters of a camera according to claim 12, wherein the geometric figure is composed of a plurality of concentric circles, concentric squares, concentric triangles or concentric polygons. 15. The method for measuring and obtaining the optical projection parameters of a camera according to claim 12, characterized in that said lens with axisymmetric nonlinear distortion is a fisheye lens. 16. The method for measuring and obtaining optical projection parameters of a camera according to claim 12, characterized in that said projection mode is a known nonlinear projection mode. 17. The method for measuring and obtaining optical projection parameters of a camera according to claim 12, wherein the projection mode is one selected from the group consisting of equidistant projection, right-angle projection and stereoscopic image projection . 18. The method for measuring and obtaining camera optical projection parameters according to claim 12, characterized in that the fixed point is the projection center of the camera lens, and the image height of at least one geometric figure and its corresponding incidence The angle between the light and the optical axis is substituted into the projection mode for calculation, which is the equivalent focal length of the camera lens. 19. The method for measuring and obtaining optical projection parameters of a camera according to claim 11, wherein said calibration object has at least one plane to provide the test pattern. 20. The method for measuring and obtaining the optical projection parameters of a camera according to claim 19, characterized in that a surrounding surface is vertically extended around the plane, so that the calibration object becomes a hollow tank with one end open shape. 21. The method for measuring and obtaining optical projection parameters of a camera according to claim 12, characterized in that said camera is a group selected from a CCD camera, a CMOS camera, a digital camera and a traditional film camera one of the .

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