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Camera intrinsic matrix (3 by 3 matrix) has a negative value and only values on main diagonal? #221
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I recorded a simulation by moving around with my camera and viewing a bunch of static objects. The camera intrinsic parameters were recorded as camera_intrinsic and extrinsic parameters were recorded as translation and rotation inside ego of the capture JSON (please correct me if this is wrong).
Now, I am experimenting with some triangulation methods (localizing objects using their 2D bounding box and the camera's projection matrix). Below is how I set up everything to get the projection matrix:
When I input the projection matrix and 2d bounding box into my custom algorithm, I noticed the triangulation was well-off. It was then that I noticed the matrix of intrinsic parameters only had values on the main diagonal and one of them is actually negative. I come from a computer vision background but not a computer graphics one. Can anyone here guide me on how to convert the intrinsic matrix provided by Unity Perception into a normal one with fx, fy, cx, cy, and skew?
I looked at the 3D Ground Truth Bounding Boxes inside the Perception_Statistics notebook but the authors seem to be considering the intrinsic parameter matrix as the projection matrix (Isn't the projection matrix supposed to be 3 by 4 due to the matrix multiplication of the 3 by 3 intrinsic parameter matrix with the 3 by 4 extrinsic parameter matrix?).
Furthermore, I also had a look at a similar question but the accepted answer there seems to assume the projection matrix is already provided while one of the answers is trying to use the FOV even though I don't see it in the data I have collected through Unity Perception.
For reference, below are the two relevant parts of the capture JSON file I am using:
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