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XYZ coordinates with stereo vision

Hello everyone,

I work on a project where the goal is to detect and track and object, and then be able to compute the XYZ coordinates of the center of this object. I need you because I'm having some trouble understanding the reference point of my coordinate system. Below, you can see what are the results I get and I circled in red the XYZ coordinates I get. I thought that the reference point of these coordinates was the middle of my left camera, as all the calibration process has been done with the left camera as a reference. But the coordinates do not refer to the left camera lens as I tought, there are offset and so it probably means that the reference point is supposed to be somewhere else ....

Results :

image description

Until know, I have been able to compute a disparity map that looks not too bad after having done all the necessary steps (individual camera calibration, stereo calibration, rectification and undistortion). The disparity map has been generated using the SGBM algorithm and then the WLS filter has been used to finally get the disparity map shown above. The next step was to track an object using the CSRT algorithm, compute the center of that object and then look the disparity value at that point on the disparity map. Once this has been done, I thought that the XYZ coordinates of the center of the object could be obtained by computing :

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with Q matrix :

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By doing this, does anyone know what is the reference point of the XYZ coordinates that I compute if it is not the left camera lens ?

Thank you.