In stereocalibration, is the relationship between the 'R and T output as PoseCamera2' and the actual camera position the same, or does the sign of x in T reverse?
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I am currently calibrating four cameras (Camera1, Camera2, Camera3, Camera4). To do this, I have created pairs (Camera1 & Camera2, Camera2 & Camera3, Camera1 & Camera4) and performed calibration to determine the relative positions of all cameras in the coordinate system of Camera1. For Camera1 and Camera2, I added about 80 images of a checkerboard taken using the stereocalibration feature of the calibration app for calibration.
As a result, I obtained the following:
R = [0.794, -0.0318, 0.605; 0.0226, 0.999, 0.0228; -0.606, -0.00446, 0.795]
T = [-2793, 44.86, 483.2] (units in [mm]).
The visual output, which I have attached as an image, shows that rotating Camera2 by R and translating it by T to align with the coordinate system of Camera1 makes it coincide with Camera1. Therefore, it can be seen that R and T correspond with the visual output.
However, the actual relative position of Camera2 to Camera1 in the coordinate system of Camera1 should be [2793, 44.86, 482.3]. Thus, I am considering that the sign of the x component of T obtained through stereocalibration might be reversed compared to the actual T. Is my understanding incorrect?
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Qu Cao
2024년 6월 12일
Sorry for the confusion. We will update our documenation to be more specific about the meaning of PoseCamera2.
PoseCamera2 is the relative pose that transforms camera 2 pose into camera 1 pose. If you represent the pose of camera 1 as [R1, t1; 0 1], pose of camera 2 as [R2, t2; 0 1], and PoseCamera2 as [R, t; 0 1]. Then you will get the following relationship:
[R1, t1; 0 1] = [R, t; 0 1] * [R2, t2; 0 1]
which gives you
R1 = R*R2
and
t1 = R*t2+t
In the plot, the x component of t2 is positive, if you add R*t2 with t, which is negative, you get t1, which is equal to zero.
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Qu Cao
2024년 6월 17일
- R and t doens't depend on the coordinate system in which camera 1 pose and camera 2 pose are represented. The coordiante system used in stereo camera calibration is described here. Essentially, In a stereo system, the origin is located at the optical center of camera 1.
- If you want to do 3-D reconstruction from disparity, I would recommend using the reprojection matrix returned by rectifyStereoImages. Once you rectify the stereo image, the cameras will be "rotated" so that their Z-axis are in parallal. Please also check the second syntax of rectifyStereoImages which might be helpful for you to do cooridnate transformation between unrectified and rectified camera coordinate systems.
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