CN105976374A - Field-related distortion calibration method of photogrammetric camera - Google Patents

Abstract

The invention provides a field-related distortion calibration method of a photogrammetric camera in an out-of-focus state. The method includes steps of a) establishing an echo light reflection co-plane linear array field used for field-related distortion calibration; b) adjusting the focusing state of the to-be-calibrated camera according to the field depth of a survey environment and the distance requirement and fixing an imaging system of the camera so as to disable the focusing function; c) establishing a field-related radial distortion model in an arbitrary focusing state; d) calibrating the field-related distortion calibration parameters, namely, radial distortion parameters, in two different distances and deducing distortion parameters of space points in other arbitrary distance on a camera image plane; e) utilizing the radial distortion parameters obtained in step d) for calculating radial distortion volume in different imaging diameters.

Description

Method for calibrating field-related distortion of photogrammetric camera

Technical Field

The invention relates to a method for calibrating distortion parameters of a camera, in particular to a method for calibrating field-related distortion of a photogrammetric camera when a plurality of industrial cameras are used for large-size and dynamic three-dimensional measurement.

Background

Along with the continuous progress of the industry, the relation between the industry and aerospace, military, engineering construction and new energy development is more and more compact, the requirements for various large-size, high-precision, real-time dynamic and even non-contact measurement are more and more increased, and photogrammetry has been widely tried and applied in relevant fields abroad.

Currently, the most widely used nonlinear distortion models include radial distortion, centrifugal distortion, and various additional distortions. The fundamental reason why the model and the calibration method are directly applied to large-size stereo measurement is that the relation between the distortion quantity, the object distance and the focusing state is neglected, and the distortion parameter is mistakenly considered to be constant.

In the aspect of the problem, the traditional photogrammetry well solves the problem, because of the multi-station measurement network with reasonable planning and high redundancy, the beam adjustment can realize the self-calibration of the parameters in the camera during the measurement, and the calibration result is closely related to the measured distance, the measurement range and even the environmental factors.

The present study is directed to the industrial measurement camera with fixed focusing state indicated in the aforementioned application field, and provides a method for calibrating the distortion model in a more general defocusing state by studying the model of the distortion parameter of the object distance change to the imaging point.

Disclosure of Invention

In order to solve the above technical problem, the present invention provides a method for calibrating field-related distortion of a photogrammetric camera, comprising the steps of: a) establishing a return light reflection coplanar linear array field for calibrating field-related distortion; b) adjusting the focusing state of a camera to be calibrated according to the requirements of the depth of field and the distance of a measuring environment, and fixing an imaging system of the camera to prevent the camera from focusing; c) establishing a field-related radial distortion model in any focusing state; d) calibrating the field-related distortion calibration parameters, namely radial distortion parameters, at two different distances, and deducing to obtain the distortion parameters of space points at any other distance on the image surface of the camera; e) and d, calculating the radial distortion quantity on different imaging radii by using the radial distortion parameters acquired in the step d.

Preferably, the step of establishing a field-dependent distortion calibration field in step a) is:

a1) unfolding the frame, supporting a movable joint of the frame by using a connecting rod, and keeping the frame stable;

a2) fixing linear materials at the upper end and the lower end of the frame vertically in parallel, stretching the linear materials, and keeping the linearity of the linear materials;

a3) and the coding points are arranged on the connecting rod and used for measuring and adjusting the angle of the optical axis of the camera during calibration.

Preferably, the frame is a stretching frame, which can be contracted and expanded; the frame has a deployed dimension of at least 3 meters in length and 2 meters in height.

Preferably, the background of the frame is arranged as a black light absorbing fleece for reducing imaging background noise from ambient light.

Preferably, the linear material is provided as a retro-reflective line having a width determined by the distance of the camera from the calibration field at the time of calibration.

Preferably, the light reflecting material of the light returning reflection lines is glass beads.

Preferably, the linear material is stretched by arranging G-clips at upper and lower ends of the frame.

Preferably, the method for establishing the radial distortion model in the step c) comprises the following steps:

c1) setting the camera phase to focus at S distance, the measured point is located at S distance from the camera₁Obtaining radial distortion on an object plane;

c2) setting the camera to focus on S₁The radial distortion parameter of the focal plane at object distance isObtaining the radial distance on the image surface in the focusing state asThe amount of radial distortion at any image point of (a);

c3) then setting the image plane of the camera to focus at the distance S, and obtaining the S by utilizing the similarity analysis of the defocusing distortion₁Distortion of an object point on a distance plane on an image plane of a camera.

Preferably, the calibration method of the radial distortion parameter in the step d) includes:

d1) setting the camera phase plane to focus on the S distance, and calibrating the two distances S by using the coplanar linear array field₁And S₂The radial distortion parameter of (1) isAnd

d2) given a known lens focal length f, S is recorded while measuring during calibration₁And S₂To find the image distanceAnd

d3) c, establishing a calibration result of the radial distortion parameter in the defocusing state by using the conclusion in the step CAnddistortion parameter in-focus stateAnda mathematical relationship therebetween;

d4) according to the Brown model, the distortion quantity of the camera image surface focused at any distance S' is obtained according to the distortion parameters at two distances in the focusing state_rs′；

Wherein the relationship between the distortion parameter in focus at two distances and the corresponding defocus distortion parameter is known, described by d 3).

d5) Amount of distortion_rs′Out of focus to the image plane of the camera with a principal distance of C_s；

d6) Calculating each radial distortion parameter:

d7) and calculating the object distance S' and obtaining the radial distortion parameter when the image plane focuses on the distance S.

Summarizing the above method, the field dependent distortion calibration method of the photogrammetric camera of the present invention solves the following problems: the method overcomes the dependence on focusing during camera calibration, simplifies the calibration process, does not depend on accurate lens focal length and object distance measurement, and eliminates the system error caused by defocusing; after the camera is calibrated, the main distance of the camera can be fixed, and the stability of the measurement precision is ensured in the subsequent measurement; the model is very suitable for calibrating a high-precision three-dimensional measurement industrial camera, and has theoretical and practical significance for popularizing a large-size dynamic photogrammetry technology in the industrial field.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.

FIG. 1 is a flow chart of a field dependent distortion calibration method of a photogrammetric camera of the present invention;

FIG. 2a is a field of a return light reflection coplanar linear array for field dependent distortion calibration established in step a) of the present invention;

FIG. 2b is a diagram of the arrangement of the G-clamp fixed linear material in the return light reflecting coplanar linear array field for field dependent distortion calibration established in step a) of the present invention.

FIG. 2c is an expanded state of the frame;

fig. 3 is a modeling diagram of a field dependent radial distortion model.

Detailed Description

The objects and functions of the present invention and methods for accomplishing the same will be apparent by reference to the exemplary embodiments. However, the present invention is not limited to the exemplary embodiments disclosed below, and may be implemented in various forms. The nature of the description is merely to assist those skilled in the relevant art in a comprehensive understanding of the specific details of the invention.

The invention provides a method for calibrating a distortion model in a more universal out-of-focus state by researching a model of object distance change to an imaging point distortion parameter for an industrial measurement camera in a fixed in-focus state.

The object to be measured in the invention has large volume, the depth range of the camera in the direction of the optical axis is large, and target points at different distances have different distortion parameters on an imaging surface, so that calibration needs to be carried out in a special large calibration field; the used industrial camera does not have automatic focusing capability, focusing errors of 0.5 to 1 pixel inevitably exist by depending on manual image focusing, and simulation analysis indicates that the focusing errors can bring huge calibration errors to the small-aperture camera; the photogrammetry needs to ensure the stability of the internal parameters of the camera, and the acquisition of the focal plane position by changing the image distance (focusing) is not beneficial to ensuring the measurement precision. Therefore, the invention researches a model and a method for calibrating distortion parameters related to object distance under the condition that the camera fixes the principal distance and the defocusing state.

As shown in fig. 1, a flow chart of a method for calibrating field-dependent distortion of a photogrammetric camera according to the present invention includes the steps of:

step 101: establishing a return light reflection coplanar linear array field for calibrating field-related distortion;

as shown in fig. 2a, the retro-reflective coplanar linear array field for field-dependent distortion calibration described in step a) includes a frame 201, a linear material 202, an encoding point 203, a black light-absorbing lint 204, a connecting rod 205, and a G-shaped clamp 206;

FIG. 2b is a view of the arrangement of the linear material held by the G-clamp;

fig. 2c shows the frame 201 in an unfolded state, wherein the connecting rods 205 are used to support the frame 201.

According to an embodiment of the present invention, the step of establishing the field-dependent distortion calibration field in the step a) is:

a1) unfolding the frame 201, supporting a movable joint 207 of the frame 201 by using a connecting rod 205, and keeping the frame 201 stable;

a2) fixing a linear material 202 vertically and parallelly at the upper end and the lower end of the frame 201, stretching the linear material 202, and keeping the linearity of the linear material 202;

a3) the encoding point 203 is arranged on the connecting rod 205 for measuring and adjusting the angle of the optical axis of the camera during calibration.

According to one embodiment of the invention, the frame is a tension frame, capable of being contracted and expanded; the frame 201 has a deployed dimension of at least 3 meters in length and 2 meters in height, as shown in fig. 2 c.

According to an embodiment of the invention, the background of said frame 201 is arranged as black light absorbing lint 204 for reducing imaging background noise from ambient light.

According to one embodiment of the present invention, the linear material 202 is configured as a back-light reflection line having a width determined by the distance of the camera from the calibration field during calibration.

According to one embodiment of the present invention, the light reflecting material of the light reflecting line is glass beads.

According to an embodiment of the present invention, the linear material 202 is stretched by arranging G-shaped clips 206 at the upper and lower ends of the frame 201, as shown in fig. 2b, which is a layout diagram for fixing the linear material by the G-shaped clips; the linear material 202 is stretched by the G-clip 203.

Step 102: adjusting the focusing state of a camera to be calibrated according to the requirements of the depth of field and the distance of a measuring environment, and fixing an imaging system of the camera to prevent the camera from focusing;

step 103: establishing a field-related radial distortion model in any focusing state;

as shown in fig. 3, a schematic diagram of a modeling of a field-dependent radial distortion model is shown:

wherein: object space point P is located on the object plane at a distance S1 from camera C_s1Is the focal plane that satisfies the gaussian imaging formula;cs is the actual image plane position of the camera.Is the radial distortion at the image point on the focal plane,is the radial distortion quantity transmitted to the actual image surface by the light. We can calibrate C_s1And the radial distortion parameters on the focal plane need to be analyzed through a similar triangle to obtain the corresponding distortion parameters and distortion quantity on the actual Cs image plane. Regarding the relationship between the two and the relationship between the radial distortion amounts on the two image planes, it can be found by the following deduction.

According to an embodiment of the present invention, the method for establishing the radial distortion model in step 103 is:

c1) setting the camera phase to focus at S distance, the measured point is located at S distance from the camera₁In the object plane, the radial distortion is described by the following polynomial equation:

_r＝k₁r³+k₂r⁵+k₃r⁷

c2) setting the camera to focus on S₁The radial distortion parameter of the focal plane at object distance isObtaining the radial distance on the image surface in the focusing state asThe radial distortion amount at any image point of (a) is:

${\mathrm{\δ}}_{{\mathrm{rs}}_1}=k_{1s_1}{r_{s_1}}^3+k_{2s_1}{r_{s_1}}^5+k_{3s_1}{r_{s_1}}^7$

c3) then setting the image plane of the camera to focus at the distance S, and obtaining the S by utilizing the similarity analysis of the defocusing distortion₁The distortion of the object point on the distance plane on the camera image plane is:

${\mathrm{\δ}}_{{\mathrm{rss}}_1}\·{\mathrm{\γ}}_{{\mathrm{ss}}_1}\·{\mathrm{\δ}}_{r_{s_1}}$

wherein,is a ratio coefficient of the number of the components,and C_sAre respectively focused on S₁Image distance from the gaussian imaging model at S distance. At the same time, it can be known that:

$r_{s_1}={\mathrm{\γ}}_{{\mathrm{ss}}_1}\·r_s$

c4) rewriting the distortion formula in step c3) as:

$\begin{array}{c}{\mathrm{\δ}}_{{\mathrm{rss}}_1}={\mathrm{\γ}}_{{\mathrm{ss}}_1}\·{\mathrm{\δ}}_{r_{s_1}}={{\mathrm{\γ}}_{{\mathrm{ss}}_1}}^2{k}_{1s_1}{r_s}^3+{{\mathrm{\γ}}_{{\mathrm{ss}}_1}}^4{k}_{2s_1}{r_s}^5+{{\mathrm{\γ}}_{{\mathrm{ss}}_1}}^6{k}_{3s_1}{r_s}^7\\ =\frac{{C_{s_1}}^2}{{C_s}^2}{k}_{1s_1}{r_s}^3+\frac{{C_{s_1}}^4}{{C_s}^4}{k}_{2s_1}{r_s}^5+\frac{{C_{s_1}}^6}{{C_s}^6}{k}_{3s_1}{r_s}^7\\ =k_{1{\mathrm{ss}}_1}{r}_s^3+k_{2{\mathrm{ss}}_1}{r_s}^5+k_{3{\mathrm{ss}}_1}{r_s}^7\end{array}$

it can be seen that the radial distortion is closely related to the object distance at a fixed principal distance.

Since the radial distortion in the present invention is related to object distance, the radial distortion parameters at two distances need to be calibrated, and the radial distortion parameters at any other distance are further solved, which is the following method for solving the radial distortion parameters at any different distance.

Step 104: calibrating the field-related distortion calibration parameters, namely radial distortion parameters, at two different distances, and deducing to obtain the distortion parameters of space points at any other distance on the image surface of the camera;

according to an embodiment of the present invention, the method for calibrating the radial distortion parameter in step 104 includes:

d1) setting the camera phase plane to focus on the S distance, and calibrating the two distances S by using the coplanar linear array field₁And the radial distortion parameters at S2, respectivelyAnd

step c4) acquires that the camera phase is focused on S and the object point is positioned on S₁The radial distortion on the image surface, similarly, is focused on S and the object point is located at a distance of S for the camera image surface₂In time, the radial distortion model on the image plane:

$\begin{array}{c}{\mathrm{\δ}}_{{\mathrm{rss}}_2}=\frac{{C_{s_2}}^2}{{C_s}^2}{k}_{1s_2}{r_s}^3+\frac{{C_{s_2}}^4}{{C_s}^4}{k}_{2s_2}{r_s}^5+\frac{{C_{s_2}}^6}{{C_s}^6}{k}_{3s_2}{r_s}^7\\ =k_{1{\mathrm{ss}}_2}{r_s}^3+k_{2{\mathrm{ss}}_2}{r_s}^5+k_{3{\mathrm{ss}}_2}{r_s}^7\end{array}$

under the experimental environment, the radial distortion parameter on the camera image surface at any distance can be calibrated by establishing a specific calibration field, namelyAnd

d2) given a known lens focal length f, S is recorded while measuring during calibration₁And S₂The precise value of (A) is obtained by the following formulaAnd

$\frac{1}{C_{s_1}}+\frac{1}{s_1}=\frac{1}{f},\frac{1}{C_{s_2}}+\frac{1}{s_2}=\frac{1}{f}$

d3) using the conclusion in step 103, the calibration result of the radial distortion parameter in the out-of-focus state can be established by the formula in c4Anddistortion parameter in-focus stateAndthe mathematical relationship between:

$\frac{1}{{C_s}^2}{k}_{1s_1}=\frac{1}{{C_{s_1}}^2}{k}_{1{\mathrm{ss}}_1},\frac{1}{{C_s}^2}{k}_{1s_2}=\frac{1}{{C_{s_2}}^2}{k}_{1{\mathrm{ss}}_2}$

$\frac{1}{{C_s}^4}{k}_{2s_1}=\frac{1}{{C_{s_1}}^4}{k}_{2{\mathrm{ss}}_1},\frac{1}{{C_s}^4}{k}_{2s_2}=\frac{1}{{C_{s_2}}^4}{k}_{2{\mathrm{ss}}_2}$

$\frac{1}{{C_s}^6}{k}_{3s_1}=\frac{1}{{C_{s_1}}^6}{k}_{3{\mathrm{ss}}_1},\frac{1}{{C_s}^6}{k}_{3s_2}=\frac{1}{{C_{s_2}}^6}{k}_{3{\mathrm{ss}}_2}$

d4) when the distortion parameter focusing on two distances is knownAndaccording to the Brown model, acquiring the distortion quantity of the camera image surface focused at any distance S' according to the distortion parameters at two distances in a focusing state;

_rs′＝k_1s′r_s′ ³+k_2s′r_s′ ⁵+k_3s′r_s′ ⁷

wherein:

$k_{1s^{\′}}={\mathrm{\α}}_{s^{\′}}{k}_{1s_1}+(1-{\mathrm{\α}}_{s^{\′}})k_{1s_2}$

$k_{2s^{\′}}={\mathrm{\α}}_{s^{\′}}{k}_{2s_1}+(1-{\mathrm{\α}}_{s^{\′}})k_{2s_2}$

$k_{3s^{\′}}={\mathrm{\α}}_{s^{\′}}{k}_{3s_1}+(1-{\mathrm{\α}}_{s^{\′}})k_{3s_2}$

${\mathrm{\α}}_{s^{\′}}=\frac{S_2-S^{\′}}{S_2-S_1}\·\frac{S_1-f}{S^{\′}-f}$

α_s′are calculable quantities.

Wherein the relationship between the distortion parameter in focus at two distances and the corresponding defocus distortion parameter is known, described by d 3).

d5) Amount of distortion_rs′Out of focus to the image plane of the camera (main distance C)_s) Obtaining:

_rss′＝γ_ss′ ²k_1s′r_s ³+γ_ss′ ⁴k_2s′r_s ⁵+γ_ss′ ⁶k_3s′r_s ⁷

＝k_1ss′r_s ³+k_2ss′r_s ⁵+k_3ss′r_s ⁷

wherein:

${\mathrm{\γ}}_{{\mathrm{ss}}^{\′}}=\frac{C_{s^{\′}}}{C_s}$

C_s′is a calculable quantity;

d6) calculating each radial distortion parameter:

$k_{1{\mathrm{ss}}^{\′}}={C_{s^{\′}}}^2{\mathrm{\α}}_{s^{\′}}\frac{1}{{C_s}^2}{k}_{1s_1}+{C_{s^{\′}}}^2(1-{\mathrm{\α}}_{s^{\′}})\frac{1}{{C_s}^2}{k}_{1s_2}$

$k_{2{\mathrm{ss}}^{\′}}={C_{s^{\′}}}^4{\mathrm{\α}}_{s^{\′}}\frac{1}{{C_s}^4}{k}_{2s_1}+{C_{s^{\′}}}^4(1-{\mathrm{\α}}_{s^{\′}})\frac{1}{{C_s}^4}{k}_{2s_2}$

$k_{3{\mathrm{ss}}^{\′}}={C_{s^{\′}}}^6{\mathrm{\α}}_{s^{\′}}\frac{1}{{C_s}^6}{k}_{3s_1}+{C_{s^{\′}}}^6(1-{\mathrm{\α}}_{s^{\′}})\frac{1}{{C_s}^6}{k}_{3s_2}$

d7) calculating the object distance at S', and obtaining the radial distortion parameter when the image plane focuses at the distance S:

$k_{1{\mathrm{ss}}^{\′}}={\mathrm{\α}}_{s^{\′}}\frac{{C_{s^{\′}}}^2}{{C_{s_1}}^2}{k}_{1{\mathrm{ss}}_1}+(1-{\mathrm{\α}}_{s^{\′}})\frac{{C_{s^{\′}}}^2}{{C_{s_2}}^2}{k}_{1{\mathrm{ss}}_2}$

$k_{2{\mathrm{ss}}^{\′}}={\mathrm{\α}}_{s^{\′}}\frac{{C_{s^{\′}}}^4}{{C_{s_1}}^4}{k}_{2{\mathrm{ss}}_1}+(1-{\mathrm{\α}}_{s^{\′}})\frac{{C_{s^{\′}}}^4}{{C_{s_2}}^4}{k}_{2{\mathrm{ss}}_2}$

$k_{3{\mathrm{ss}}^{\′}}={\mathrm{\α}}_{s^{\′}}\frac{{C_{s^{\′}}}^6}{{C_{s_1}}^6}{k}_{3{\mathrm{ss}}_1}+(1-{\mathrm{\α}}_{s^{\′}})\frac{{C_{s^{\′}}}^6}{{C_{s_2}}^6}{k}_{3{\mathrm{ss}}_2}$

step d7) shows that any two distances S can be passed₁And S₂And calculating the radial distortion parameters at other distances S' according to the calibration result of the radial distortion parameters. It has also been shown that this method does not even require measuring the focal distance S or C of the camera image plane_sGo forward and go forwardThe calibration workload is reduced in one step.

Step 105: the radial distortion amount at different imaging radii is calculated using the radial distortion parameters obtained in step 104.

The field-related distortion calibration method of the photogrammetric camera is verified through the following experiments.

Fig. 2 shows a distortion parameter calibration field in which several coplanar retro-reflective straight lines are arranged. Due to the presence of distortion, linear arrays are imaged as curved arrays with a certain regularity. Through a complex nonlinear least square adjustment method, the distortion parameter for correcting the curve into a straight line is the distortion parameter of the imaging system.

First, the variation of radial and eccentric distortions with object distance was studied.

The industrial camera used in the experiment is AVT GE4900, which has a full-frame sensor with 1600 ten thousand pixel resolution, two fixed-focus full-frame lenses with focal lengths of 50mm and 35mm for the experiment, and the lenses are respectively focused at an unknown distance. The radial and eccentric distortion parameters were calibrated at different distances, while the radial and eccentric distortion quantities at different imaging radii were calculated, with the results shown in tables 1 and 2.

TABLE 1 variation of radial distortion and eccentric distortion of 50mm lens at different distances and radii

TABLE 2 variation of radial distortion and eccentric distortion of 35mm lens at different distances and radii

From the calibration results of the two lenses, the radial distortion amount generates a non-negligible change amount along with the change of the object distance, while the eccentric distortion amount keeps stable, thereby verifying the theoretical analysis of the two distortions.

Then, the two distortions are calibrated and verified by a calculation method

The distortion amount at the other distances is calculated using the calibration results at the two distances, and then compared with the calibration results of the distortion amount at the present distance, and the results are shown in tables 3 and 4.

TABLE 3 calculation of radial distortion at other distances using calibration results from 2 nd and 3 rd times of the 50mm lens

TABLE 4 calculation of radial distortion at other distances using calibration results from 2, 5 times of 35mm lens

The deviation between the calculation result and the calibration result is mostly less than 1 micron, especially for the calibration of a 35mm lens, so that the theoretical model of the radial distortion calibration method is verified. For comparison, the calibration results at a certain distance are directly used to calculate the distortion amount at other distances, without considering the relationship between the radial distortion amount and the object distance, and the results are also compared with the calibration results, and the results are shown in tables 5 and 6.

Radial distortion and error of 550 mm lens without considering object distance

Radial distortion and error of 635 mm lens without considering object distance influence

The comparative data in tables 5 and 6 illustrate that large systematic errors occur when radial distortion variations due to object distance are not taken into account. Considering the object distance-distortion model of the present invention, this systematic error is greatly reduced.

The experiments prove that in the defocus distortion model provided by the invention, the radial distortion obviously changes along with the object distance, and the eccentric distortion does not change;

the calibration model and the calibration method in the out-of-focus state provided by the invention can calibrate the industrial camera with any focusing distance. The method is suitable for the camera for industrial measurement with fixed main distance, overcomes the influence caused by focusing error, even does not need to know the focusing distance of the camera, and greatly improves the calibration efficiency and the subsequent measurement precision;

the invention provides a method for calculating the radial distortion parameter of any other distance by using the radial distortion calibration result of any two distances, and calculating the eccentric distortion parameter of any other distance by using the eccentric distortion calibration result of any one distance, wherein the error of the calculation result is very small.

The method overcomes the dependence on focusing during camera calibration, simplifies the calibration process, does not depend on accurate lens focal length and object distance measurement, and eliminates the system error caused by defocusing; after the camera is calibrated, the main distance of the camera can be fixed, and the stability of the measurement precision is ensured in the subsequent measurement; the model is very suitable for calibrating a high-precision three-dimensional measurement industrial camera, and has theoretical and practical significance for popularizing a large-size dynamic photogrammetry technology in the industrial field.

The above description is only exemplary of the invention and should not be taken as limiting the scope of the invention, which is intended to include all equivalent variations or modifications of the structure, features and principles of the invention as described in the claims.

Claims (9)

1. A field-dependent distortion calibration method for a photogrammetric camera is characterized by comprising the following steps:

a) establishing a return light reflection coplanar linear array field for calibrating field-related distortion;

b) adjusting the focusing state of a camera to be calibrated according to the requirements of the depth of field and the distance of a measuring environment, and fixing an imaging system of the camera to prevent the camera from focusing;

c) establishing a field-related radial distortion model in any focusing state;

d) calibrating field-related distortion calibration parameters, namely radial distortion parameters, at two different distances to obtain distortion parameters of space points at the image surface of the camera at any other distance;

e) and d, calculating the radial distortion quantity on different imaging radii by using the radial distortion parameters acquired in the step d.

2. The method for calibrating field dependent distortion as set forth in claim 1, wherein the step of establishing the field dependent distortion calibration field in step a) comprises:

a1) unfolding the frame, supporting a movable joint of the frame by using a connecting rod, and keeping the frame stable;

a2) fixing linear materials at the upper end and the lower end of the frame vertically in parallel, stretching the linear materials, and keeping the linearity of the linear materials;

a3) and the coding points are arranged on the connecting rod and used for measuring and adjusting the angle of the optical axis of the camera during calibration.

3. The method for calibrating field dependent distortion of claim 2, wherein: the frame is a stretching frame and can be contracted and expanded; the frame has a deployed dimension of at least 3 meters in length and 2 meters in height.

4. The method for calibrating field dependent distortion of claim 2, wherein: the background of the frame is arranged as black light absorbing lint for reducing imaging background noise from ambient light.

5. The method for calibrating field dependent distortion of claim 2, wherein: the linear material is arranged as a light return reflection line having a width determined by the distance of the camera from the calibration field when calibrating.

6. The method for calibrating field dependent distortion of claim 2, wherein: the reflecting material of the return light reflecting line is glass beads.

7. The method for calibrating field dependent distortion of claim 2, wherein: the stretching method of the linear material comprises the steps that G-shaped clamps are arranged at the upper end and the lower end of the frame, and the linear material is stretched through the G-shaped clamps.

8. The method for calibrating field dependent distortion of claim 1, wherein the method for establishing the radial distortion model in step c) comprises:

c1) setting a camera phase plane to focus at a distance S, and positioning a measured point on an object plane at a distance S1 from the camera to obtain a radial distortion;

c2) setting the camera to focus on S₁The radial distortion parameter of the focal plane at object distance isObtaining the radial distance on the image surface in the focusing state asThe amount of radial distortion at any image point of (a);

c3) then setting the image plane of the camera to focus at the distance S, and obtaining the S by utilizing the similarity analysis of the defocusing distortion₁Distortion of an object point on a distance plane on an actual image plane of the camera.

9. The method for calibrating field dependent distortion as set forth in claim 1, wherein the method for calibrating radial distortion parameters in step d) comprises:

d1) setting the camera phase plane to focus on the S distance, and calibrating the two distances S by using the coplanar linear array field₁And S₂The radial distortion parameter of (1) isAnd

d2) given a known lens focal length f, the distance S is recorded while measuring at the time of calibration₁And S₂To find the image distanceAnd

d3) c, establishing a calibration result of the radial distortion parameter in the defocusing state by using the conclusion in the step CAnddistortion parameter in-focus stateAnda mathematical relationship therebetween;

d4) according to the Brown model, the distortion quantity of the camera image surface focused at any distance S' is obtained according to the distortion parameters at two distances in the focusing state_rs′；

Wherein the relationship between the distortion parameter in focus at two distances and the corresponding defocus distortion parameter is known, described by d 3).

d5) Amount of distortion_rs′Defocusing to an image surface of the camera;

d6) calculating each radial distortion parameter:

d7) and calculating the object distance S' and obtaining the radial distortion parameter when the image plane focuses on the distance S.