[ros-users] accelerometer and tilt support + depth function

Stéphane Magnenat stephane at magnenat.net
Mon Nov 15 17:10:32 UTC 2010


I have integrated the accelerometer and tilt support from adafruit [1] 
into my kinect node. To do so, I have added them to libfreenect, for 
which I now provide a git with my changes instead of patches in my 
kinect node [3].

Here at ASL, Deon Sabatta and Davide Scaramuzza have found a more 
precise depth function than 1/x. It is the following:

	depth = k3 * tan(pixVal/k2 + k1)


	k1 = 1.1863
	k2 = 2842.5
	k3 = 0.1236

"The k2 value is very sensitive and may require more/better 
measurements; however, this is a pretty good approximation for the moment."

I would like to raise two questions:

1. Having multiple implementations of Kinect ROS nodes is not harmful as 
we happily share code. However, to ease the end-user's life I think that 
we should agree on a naming convention for node and topic naming. Here 
is a first suggestion:
   node name: "kinect"
   point cloud frame: "/kinect"
   point could topic: "/kinect/cloud" (PointCloud + color in "rgb")
   rgb image topic: "/kinect/image" (Image, rgb)
   depth (raw in 8bpp) image topic: "/kinect/depth_image" (Image, mono8)
   accelerometer topic: "/kinect/acc" (Vector3)
   tilt input: "/kinect/tilt" (Int16)
Feel free to discuss it and propose more conventions, for instance for 
the params/etc.

2. I have branched libfreenect to provide updates more easily to the ROS 
community, but I do not want to fork it. Hector, your input is warmly 
welcome on my changes. Currently, libfreenect is not reentrant and does 
not have clean naming prefixes. The reentrance might require a bit of 
thinking, but the naming is straightforward; do you agree if I put a 
heading kinect_ before all public functions?

I'm looking forward to hearing your comments, dear kinect hackers.

Kind regards,


[1] https://github.com/adafruit/Kinect
[2] https://github.com/ethz-asl/ros-drivers/tree/master/microsoft_kinect/
[3] https://github.com/stephanemagnenat/libfreenect

Dr Stéphane Magnenat

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