CN102096918B - Calibration method of parameters of camera for rendezvous and docking - Google Patents

Abstract

The invention discloses a calibration method of parameters of camera for rendezvous and docking, which is a method for calibrating and accurately establishing a camera coordinate system of an effective focus of a camera and an image center by adopting an optical external standard method. The invention solves the technical problems that position measurement accuracy and posture measurement accuracy are difficult to simultaneously realize and the position measurement accuracy along a viewing direction is low through establishing a coordinate axis in a camera viewing direction by utilizing an optical lens optical axis direction reference, adopting the thought that the focus in a camera measurement mathematic model changes along with the change of distance to establish an effective focus curve.

Description

A kind of intersection docking scaling method of camera intrinsic parameter

Technical field

The present invention relates to a kind of scaling method of camera intrinsic parameter.

Background technology

CCD optical imagery sensor is the crucial measurement component of intersection docking mission, is comprised of CCD camera and target marker.The CCD camera is installed on the tracker, and target marker is by being installed on the target aircraft.Its function be when tracker docks with the target aircraft intersection in the certain distance scope, to target marker imaging and measurement, obtain the optical sensor coordinate system with respect to relative position and the relative attitude angle of target marker coordinate system by the CCD camera.

One of CCD optical imagery sensor development difficult point is to require to have in the certain distance scope higher position and orientation measurement precision.Existing method is mainly used the information of having utilized fixed form information and imaging point, can calculate the inner parameter of camera.In the monocular vision real-time measurement system, need to correct in real time the distortion of imaging point, obtain the coordinate of ideal image point, and calculate thus the pose parameter between target and camera.Zhang Zheng-you for example, A flexible new technique for camera calibration, Technical Report MSR-TR-98-71,1998 disclosed scaling methods, masterplate can not guarantee along the high-precision realization of direction of visual lines position measurement owing to adopting fixedly in the calibration process, and the fixing measurement meeting of masterplate produced a very large impact calibration result, thereby affect the normal measurement of CCD optical imagery sensor.

Summary of the invention

Technology of the present invention is dealt with problems and is: overcome prior art and be difficult to realize simultaneously the position and orientation measurement precision, and along the lower technical barrier of direction of visual lines positional accuracy measurement, proposed the scaling method that the camera intrinsic parameter is used in a kind of intersection docking.

Technical solution of the present invention is: a kind of intersection docking scaling method of camera intrinsic parameter, and step is as follows:

(1) sets up CCD camera coordinates system, initial point is the normal intersection point spatially of crossing cross groove center of orthogonal three faces of reference mirror placed on the CCD camera, the normal direction of the minute surface of normal and reference mirror front end face normal parallel is Z axis in described three faces, the normal direction of pointing to the benchmark minute surface of the earth direction is Y-axis, and X-axis and Y-axis and Z axis meet the right-hand rule;

(2) point of choosing uniform fold camera measuring distance and viewing field of camera utilizes the CCD camera that known measuring point is measured as known measuring point, to the centre coordinate x that practises physiognomy of camera _p, y _pAnd focal distance f _pDemarcate, step is:

(21) choose the initial value of image center coordinate and focal length

(22) calculate F _k=(f ₁, f ₂..., f _n) (f ₁, f ₂..., f _n) ^T, wherein

I=1,2....., n, n are known measuring point number,＜the expression inner product operation,

Be i the coordinate of known measuring point under earth coordinates, χ _jThe coordinate that the individual known measuring point of i of measuring under diverse location for camera in the CCD camera coordinates is,

With For with χ _jThe i that measures under a corresponding position known measuring point at camera as the coordinate on the plane,

With

Be respectively the first row, the second row and the third line of matrix R, R is the transition matrix between earth coordinates and the CCD camera coordinates system;

(23) if the F that tries to achieve _kSatisfy accuracy requirement, then try to achieve

Respectively as practise physiognomy centre coordinate and the focal length of camera under i the known measuring point, otherwise adjust

Until F _kSatisfy accuracy requirement;

(24) geometric mean is carried out with the centre coordinate of practising physiognomy of camera under each the known measuring point that obtains in continuous repeating step (21)～(23), obtains the centre coordinate x that practises physiognomy of camera _p, y _p, the focal length of camera couples together the focal length curve that forms camera under the known measuring point of each that will obtain simultaneously;

(3) camera focus curve and the centre coordinate of practising physiognomy step (2) determined carry the initial value that posture position is found the solution software as camera, all known measuring points are calculated posture positions and compare with the measurement result of step (2), obtain thus the measuring error of CCD camera.

The present invention's advantage compared with prior art is: scaling method of the present invention utilizes the higher optics external standard measurement result of measuring accuracy, the camera inner parameter is demarcated, calibrating parameters is transition matrix between effective focal length, picture centre and camera coordinates system and reference mirror coordinate system, these calibrating parameters write CCD optical imagery sensor software, namely can guarantee the position and orientation measurement precision in the whole measure scope.The method mentality of designing is novel, the calibrating parameters process is simple, operand is little, take hardware resource little, and greatly improved positional accuracy measurement along direction of visual lines, overcome scaling method design complexity commonly used, operand is large, the committed memory resource is large and along the low deficiency of the positional accuracy measurement of direction of visual lines, has adapted to very much the space camera use of working environment complexity.

Description of drawings

Fig. 1 is the FB(flow block) of the inventive method.

Embodiment

As shown in Figure 1, be the theory diagram of the inventive method, key step is as follows:

(1) the CCD camera coordinates is that initial point is set up;

Utilize cross groove on the prism square face vertical with the camera optical axis that the position measurement benchmark of CCD camera is provided, can accurately locate the initial point that the CCD camera is measured coordinate system according to this benchmark, reference mirror is vertical three normal intersection points spatially of crossing cross groove center mutually, are the initial point of camera coordinates system.

(2) the CCD camera coordinates means to foundation

Utilize the cross groove on the prism square face vertical with the camera optical axis to provide three axles of CCD camera to point to measuring basis, prism square is installed on the camera body, it is the directional reference of camera, be called reference mirror, the first minute surface normal of camera lens and reference mirror front end face normal parallel are the Z axis of camera coordinates system, the benchmark minute surface normal that points to the earth direction is Y-axis, and three axles meet right-handed coordinate system.

(3) CCD camera image center and effective focal length scaling method;

After aforementioned two steps are finished, carrying out picture centre and effective focal length demarcates again, utilize CCD camera coordinates system, measure the result of test case position under the CCD camera coordinates is as the outer measured value of camera under demarcation regulation test case position, the rule that test case is chosen is uniform fold camera measuring distance and viewing field of camera.

Be the outer measured value of camera under i demarcation test case, the parameter that camera need to be demarcated (CCD image plane center coordinate and focal length) is made as

Exist as can be known according to the camera imaging formula

$f\left({\mathrm{\&Omega;}}_i\right)=\left[\begin{array}{c}(x_i^{\&prime;}-x_p^i)<{\mathrm{\&chi;}}_j-{\mathrm{\&chi;}}_i,{\hat{r}}_{3,i}>+f^i<{\mathrm{\&chi;}}_j-{\mathrm{\&chi;}}_i,{\hat{r}}_{1,i}>=0\\ (y_i^{\&prime;}-y_p^i)<{\mathrm{\&chi;}}_j-{\mathrm{\&chi;}}_i,{\hat{r}}_{3,i}>+f^i<{\mathrm{\&chi;}}_j-{\mathrm{\&chi;}}_i,{\hat{r}}_{2,i}>=0\end{array}\right]$

I=1 wherein, 2....., n, n are known measuring point number,＜the expression inner product operation, Be i the coordinate of known measuring point under earth coordinates, χ _jThe coordinate that the individual known measuring point of i of measuring under diverse location for camera in the CCD camera coordinates is,

With

For with χ _jThe i that measures under a corresponding position known measuring point at camera as the coordinate on the plane,

With

Be respectively the first row, the second row and the third line of matrix R, R is the transition matrix between earth coordinates and the CCD camera coordinates system;

For real coefficient transcendental equation group:

$\left\{\begin{array}{c}{f}_1({\mathrm{\&alpha;}}_1,{\mathrm{\&alpha;}}_2,{\mathrm{\&alpha;}}_3)=0\\ f_2({\mathrm{\&alpha;}}_1,{\mathrm{\&alpha;}}_2,{\mathrm{\&alpha;}}_3)=0\\ \&CenterDot;\&CenterDot;\&CenterDot;\&CenterDot;\&CenterDot;\&CenterDot;\\ f_n({\mathrm{\&alpha;}}_1,{\mathrm{\&alpha;}}_2,{\mathrm{\&alpha;}}_3)=0\end{array}\right.$

α in the formula _i(i=1,2,3) represent respectively ccd image centre coordinate and focal length.

The objective definition function:

F(α ₁，α ₂，α ₃)＝(f ₁，f ₂，...，f _n)(f ₁，f ₂，...，f _n) ^T＝0

Obviously satisfy the α of minimal value condition this moment ₁, α ₂, α ₃It also is the solution of equation.

(31) measured value is measured confidential reference items numerical value (focal length and image plane center) for the camera of expectation measurement result Select Error minimum in addition

As initial value;

(32) calculate

(33) if F _k＜ε, ε=10 ^-8, then

Be required solution, otherwise changed for (4) step over to;

(34) to finding the solution parameter

Iterative computation, again substitution (2).

L=1,2,3,

Finish above-mentioned steps and can obtain i the intrinsic parameter of demarcating under the test case

Test case according to the rules can be set up focal distance f _pBe the focal length curve of final camera with the curve of variable in distance, the picture centre (x that different test cases are found the solution _p, y _p) carry out the result that geometric mean can obtain final camera image center.

(4) CCD camera coordinates system and reference mirror coordinate system relation are determined

The camera focus curve determined and picture centre are reentered into the camera posture position find the solution software, calculate camera result of calculation under all regulation test cases and externally measured result relatively, calculate [θ _i, φ _i, Ψ _i] the three-axis attitude measuring error, from i=1,2 ..., n carries out geometric mean, with final statistical error system's constant error the most, is used for the final measurement correction, i.e. CCD camera final measurement=camera posture position result of calculation+system's constant error.

The content that is not described in detail in the instructions of the present invention belongs to those skilled in the art's known technology.

Claims (1)

1. the scaling method of using the camera intrinsic parameter is docked in an intersection, it is characterized in that step is as follows:

(1) sets up CCD camera coordinates system, initial point is the normal intersection point spatially of crossing cross groove center of orthogonal three faces of reference mirror placed on the CCD camera, the normal direction of the minute surface of normal and reference mirror front end face normal parallel is Z axis in described three faces, the normal direction of pointing to the benchmark minute surface of the earth direction is Y-axis, and X-axis and Y-axis and Z axis meet the right-hand rule;

(2) point of choosing uniform fold camera measuring distance and viewing field of camera utilizes the CCD camera that known measuring point is measured as known measuring point, to the centre coordinate x that practises physiognomy of camera _p, y _pAnd focal distance f _pDemarcate, step is:

(21) choose the initial value of image center coordinate and focal length

(22) calculate F _k=(f ₁, f ₂..., f _n) (f ₁, f ₂..., f _n) ^T, wherein

I=1,2....., n, n are known measuring point number,＜＞the expression inner product operation,

Be i the coordinate of known measuring point under earth coordinates, χ _jBe i the coordinate that known measuring point in the CCD camera coordinates is that camera is measured, x ' under diverse location _iAnd y ' _iFor with χ _jThe i that measures under a corresponding position known measuring point at camera as the coordinate on the plane,

With

Be respectively the first row, the second row and the third line of matrix R, R is the transition matrix between earth coordinates and the CCD camera coordinates system;

(23) if the F that tries to achieve _k＜ε, ε=10 ^-8, then try to achieve Respectively as practise physiognomy centre coordinate and the focal length of camera under i the known measuring point, otherwise adjust

Until F _k＜ε, ε=10 ^-8

(24) geometric mean is carried out with the centre coordinate of practising physiognomy of camera under each the known measuring point that obtains in continuous repeating step (21)～(23), obtains the centre coordinate x that practises physiognomy of camera _p, y _p, the focal length of camera couples together the focal length curve that forms camera under the known measuring point of each that will obtain simultaneously;

(3) camera focus curve and the centre coordinate of practising physiognomy step (2) determined carry the initial value that posture position is found the solution software as camera, utilize the CCD camera that all known measuring points are calculated posture positions and compare with the measurement result of step (2), obtain thus the measuring error of CCD camera.

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