Straight hallways appear curved in RtabMap

[scarabeo]

Hello, I mapped a rose crop, with about 36 mt long.
The rose crop is straight, no curvature.
Is there a reason why RtabMap is given me a curved map?
Could it be that kinect2 was not stable or fixed in one position?

[matlabbe]

Hi,

Make sure your depth image is correctly registered to color image. Do you use iai_kinect2 package? They have a calibration tool: kinect2_calibration. If you use RTAB-Map standalone, there is also a calibration tool in Preferences->Source->Calibrate (however, this tool cannot calibrate the depth measurements, only camera calibration and registration).

A good camera calibration and a good RGB-depth registration can decrease this curved effect.

cheers

[scarabeo]

Ummm, I just connecting the kinect2 and pressing play in RtabMap.
I thought Rtabmap calibrates internally the connected device.

Where may I check if my connected kinect2 is well calibrated?

[matlabbe]

Ok, you are using the standalone version. By default for Freenect2 driver, factory calibration is used (well the one used by libfreenect2).

You can click on "Test" button in the Preferences->Source panel to look at the point cloud generated. Make sure that color and depth match well together.

For camera calibration, you can click "Calibrate". You can look at this calibration example (see Calibration section), though you can use directly the feed of the camera (no need to record a video).

When the calibration files are saved in ~/Documents/RTAB-Map/camera_info and calibration file path is set in Source panel, the Freenect2 driver will use it.

cheers

[brigit]

Is camera calibration only needed for stereo cameras (because there are 2) or for all camera types? I am using a primesense camera and have had the same problem at times.

[matlabbe]

Hi,

Calibration for RGB-D cameras can be done too. However, unless for Freenect2, RTAB-Map standalone doesn't support calibration of RGB-D cameras (it uses always the factory calibration/registration). Not sure if OpenNI2 could load some calibration files if saved somewhere in its config folders.

ROS provides a package to calibrate RGB-D cameras: http://wiki.ros.org/openni_launch/Tutorials

Note that RGB-D cameras would need also a depth calibration to increase accuracy. Quote from this page:

This calibration does not necessary fully calibrate the depth. Especially the ASUS Xtion is prone to depth errors and needs further calibration

cheers