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Kinect calibration: disparity or depth?

asked 2012-03-01 22:25:12 -0500

dlopez gravatar image

updated 2016-10-24 09:00:37 -0500

ngrennan gravatar image

Reading the technical description in ROS wiki (http://www.ros.org/wiki/kinect_calibration/technical), one would think that kinect devices produce disparity images (with a specific normalization) and efforts should be done to estimate a baseline separation between IR camera and IR projector and a specific constant offset. However, by ROS code inspection, it appears to me that the driver gives a depth map rather than disparity and no baseline/offset calibration is used.

Is ROS kinect calibration currently based only on a zero distortion calibration of the IR camera (thus assuming an accurately measured depth and estimating real-world XY), or am I missing something?

Thanks.

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answered 2012-03-02 07:34:13 -0500

Patrick Mihelich gravatar image

The device actually sends something akin to a disparity image over USB. Both OpenNI and libfreenect are capable of converting that to a depth image using parameters reported by the device (baseline, focal length, and distance to reference plane, IIRC).

The kinect_calibration package dates from the early days of Kinect hacking, when libfreenect could only return the disparity image and OpenNI was not yet released. So calculating the disparity->depth conversion was a crucial part of calibration.

These days we can trust the driver to return an accurate depth image and work from there. openni_launch is our stable driver package. It allows you to calibrate both the IR and RGB cameras as described at http://www.ros.org/wiki/openni_camera/calibration; otherwise a default calibration is used. The lens on the IR camera is low-distortion, so modeling the distortion only slightly improves accuracy.

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Asked: 2012-03-01 22:25:12 -0500

Seen: 2,829 times

Last updated: Mar 02 '12