Problem with XYZ points obtained

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Rod Hid 2019-5-9

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https://ww2.mathworks.cn/matlabcentral/answers/461220-problem-with-xyz-points-obtained

编辑： Rod Hid 2019-6-12

Hello,

I'm trying to get the XYZ coordenates of the world using the CameraCalibrator app from 200 segmented images obtained from the capture of an object pointed with a laser line and positioned on a platform that rotates 1.8 degrees (by capture) to subsequently generate a 3d model.

To calculate the calibration matrix with the rotation of the object, I used the following lines of code:

%%
angleX = 0;
angleY = stp*(1.8); >> stp is number of step of the platform
angleZ = 0;
Rx = rotx(angleX); Ry = roty(angleY); Rz = rotz(angleZ);  
Rb = Rx*Ry*Rz;
tx = 0; ty = 0; tz = 0;
tb = [tx ty tz];
MPb = [Rb zeros(3,1); tb 1];
Rt = [RotationMatrix; TranslationVector];   
MC = Rt*IntrinsicMatrix;
P = MPb*MC;
P = P';
%%

after that, with the points (u, v) obtained from the segmented image, I calculate the XYZ points of the world using the following lines of code:

%%
%  (u*P31 - P11)X + (u*P32 - P12)Y + (u*P33 - P13)Z + (u*P34 - P14) = 0
%  (v*P31 - P21)X + (v*P32 - P22)Y + (v*P33 - P23)Z + (v*P34 - P24) = 0
for i = 1:length([u,v]) >> this is the cycle only for an image
            A = [(u(i)*P(3,1) - P(1,1)) (u(i)*P(3,2) - P(1,2)) (u(i)*P(3,3) - P(1,3)); 
                    (v(i)*P(3,1) - P(2,1)) (v(i)*P(3,2) - P(2,2)) (v(i)*P(3,3) - P(2,3))];
             b = [-(u(i)*P(3,4)) + P(1,4); 
                    -(v(i)*P(3,4)) + P(2,4)];         
             x = pinv(A)*b;
             XYZ(i,:) = x;
end
%%

When I plot the points obtained (plot_points_XYZ.png), it doesn't resemble the real shape of the object (Cap_cam1_step_01.png).

What am I doing wrong?

Thank you for your help

Rod Hid

P.S: Are the distortion values incorporated into the calculations of the intrinsic matrix, rotation matrix and translation vector delivered by the CameraCalibrator app?

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Rod Hid 2019-5-17

What is the relationship between focal length and scale?

darova 2019-5-17

I didn't know those are focal length. Just saw that image and tried to change fx, fy

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回答（2 个）

Rod Hid 2019-5-22

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https://ww2.mathworks.cn/matlabcentral/answers/461220-problem-with-xyz-points-obtained#answer_376201

I made a new calibration of the camera because the pattern presented some problems.

Could you help me find the new values for fx and fy that you calculated earlier for a better proportion of the object?

P.S: Attached the rotation matrix, translation vector, intrinsic matrix and an improved code of the projection matrix of the camera.

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darova 2019-5-23

I dont' know how to calculate them. Just try different values

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Rod Hid 2019-6-12

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/461220-problem-with-xyz-points-obtained#answer_378880

编辑：Rod Hid 2019-6-12

Is it necessary to remove the distortion from the calibration pattern to calibrate the camera and the captured images to obtain the coordinates of the laser line?