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Thank you for your interest in the Intel RealSense D435 camera.
The center of the depth can't be calculated exactly, as the filed of view is the overlap of the sensors. You can also find this information on the datasheet, page 56
At page 59, you can see that the Depth Start Point is located at -4.2mm from the Front Cover Glass. This implies that the Depth Start Point is at 20.85mm from it.
You can also check the Projection in RealSense - Point Coordinates for more useful information on this matter.
Please let me know if I can provide any other information.
Thank you Eliza for the concise reply.
I was reading the 337029-002 version of the document and the section you mention was added in 337029-003, which is great.
That said, I empirically find the depth start point (Z') to be ~11mm behind the glass on my D435 and not 4.2mm (I have spent hours averaging tens of thousands of measurements and I might be a millimetre or so off, but not 7mm).
"The center of the depth can't be calculated exactly" bothers me somewhat.
Using a depth camera to generate point clouds where solely the the distances between the points in the cloud is fine for 3D modelling but for robotics applications a point cloud is useless if one doesn't know the exact location of the origin - the vehicle sees a point cloud but doesn't know how far away it is in the vehicle's frame of reference.
That the "center of the depth is difficult to ascertain because of calibration" I can accept, but it would be really helpful if the procedure to precisely determine the origin were published.
Could you please let us know how you have calculated, empirically, the Depth Start Point?
Also, if you are interested in generating a point cloud, you can use the commands from: https://github.com/IntelRealSense/librealsense/wiki/Projection-in-RealSense-SDK-2.0#point-cloud
thanks for the follow-up.
As the Z-error issue seems closely related to my other question https://communities.intel.com/message/563508#563508 perhaps it would be best if we continued there and close this thread?