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Pi Robot
02-19-2011, 05:43 PM
[I just posted this to my little Pi Robot mailing list and thought I'd throw it up here too.]


One of the benefits of being a robot is that you can swap out your parts more-or-less at will when new gadgets appear on the market. So when the $149 Kinect camera was released for the XBox game console, the robotics community took about a week to figure out how to use the camera to give their robots 3D vision. Pi Robot has actually had a Kinect since just before Christmas (no, he couldn't wait), but today he finally got to try it on.

What you are about to see may shock you at first--Pi's familiar face has been transformed by the new technology. But as we will see, it is all for the best. Though bigger and heavier than a typical webcam, the Kinect provides both a regular color video image as well as a depth measurement at each point. It does this by projecting a pattern of structured infrared light (http://en.wikipedia.org/wiki/Structured_light)out onto the world and uses a second camera tuned to infrared wavelengths to measure the distortion of this pattern caused by the shapes of objects in the scene. The result is a full depth map of every pixel in the image and at 30 frames per second.

This first image shows Pi with his new head on.


http://www.pirobot.org/images/pi-kinect.jpg


The Kinect camera is the black horizontal device at the top. It is wide because it has to accommodate two cameras and one projector. It also has two microphones, one at either end, that can be used to locate sounds. The tufts on top of the Kinect came as a little surprise, first discovered by Mike Ferguson (a.k.a "Fergs") at the University of Albany when he built his latest creation Maxwell shown here:


http://3.bp.blogspot.com/_qmthA_fNJ-Y/TU9NC83aBiI/AAAAAAAAANU/oukkChrQO68/s1600/sm_maxwell-build-6.jpg (http://www.showusyoursensors.com/2011/02/introducing-maxwell.html)


So what do the 3-dimensional images look like? ROS includes a visualization tool called RViz which allows us to see both the regular video image and the 3D map from the Kinect. The 3D map can be shown in one of three ways: as the original RGB colors overlayed on the depth measurements; as a flat-color (e.g. gray) image; or as a color-coded image with red indicating objects closer to the camera and blue/violet labeling far away points. Here's what they look like:

RGB Mode:

http://www.pirobot.org/images/ROS/kinect/kinect-rviz-rgb.png


Flat Gray Mode:

http://www.pirobot.org/images/ROS/kinect/kinect-rviz-grey.png

Colorized Depth Mode ("Axis"):

http://www.pirobot.org/images/ROS/kinect/kinect-rviz-axis.png

The last image perhaps best illustrates the quality of the depth map returned by the Kinect, with subtle changes in hue reflecting the distance of that point in the scene from the camera. Over the next several weeks and months, Pi will use this new 3D vision ability to begin recognizing real-world objects by size and shape, much as we do. Stay tuned!


--patrick

veltrop
02-26-2011, 05:22 AM
Nice upgrade!

lnxfergy
02-26-2011, 11:12 AM
We need to get a side-by-side picture of Maxwell and Pi at Robogames....

-Fergs

Pi Robot
03-01-2011, 10:29 AM
Cheese! :D