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D435: Where is the focal point of the depth-map ?

MCalv4
Beginner
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I surmise from the drawings on page 94 of Intel-RealSense-D400-Series-Datasheet.pdf that the centre of the depth sensors is 37.5 mm from the right-side (USB side) of the camera:

and I infer, empirically, that the depth map focal point X is some 32mm behind the camera's face.

1. Is the centre indeed 37.5mm from the right?

2. What is the exact value of 'X' ?

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idata
Employee
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Hello smirkingman,

 

 

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 https://www.intel.com/content/dam/support/us/en/documents/emerging-technologies/intel-realsense-technology/Intel-RealSense-D400-Series-Datasheet.pdf 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 https://github.com/IntelRealSense/librealsense/wiki/Projection-in-RealSense-SDK-2.0# point-coordinates Projection in RealSense - Point Coordinates for more useful information on this matter.

 

 

Please let me know if I can provide any other information.

 

 

Best regards,

 

Eliza

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5 Replies
idata
Employee
1,684 Views

Hello smirkingman,

 

 

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 https://www.intel.com/content/dam/support/us/en/documents/emerging-technologies/intel-realsense-technology/Intel-RealSense-D400-Series-Datasheet.pdf 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 https://github.com/IntelRealSense/librealsense/wiki/Projection-in-RealSense-SDK-2.0# point-coordinates Projection in RealSense - Point Coordinates for more useful information on this matter.

 

 

Please let me know if I can provide any other information.

 

 

Best regards,

 

Eliza
MCalv4
Beginner
1,683 Views

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.

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idata
Employee
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Hello smirkingman,

 

 

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

 

 

Thank you,

 

Eliza
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MCalv4
Beginner
1,683 Views

Hi Eliza,

thanks for the follow-up.

As the Z-error issue seems closely related to my other question /message/563508# 563508 https://communities.intel.com/message/563508# 563508 perhaps it would be best if we continued there and close this thread?

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idata
Employee
1,682 Views

Hello smirkingman,

 

 

Sure thing!

 

 

Thank you,

 

Eliza
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