Friday, April 22, 2011

Digging more with ICP

This post is a continuation of my last post that talks about using ICP to register two coarsely registered point clouds. That post talked about getting the test.cpp code that comes with MRPT library to perform ICP on two point-clouds. That code synthetically creates two small point-clouds, introduces a random small difference in there poses, and then calls ICMP::align3D() to register the point-clouds.

My plan is to use the ICP API for kinect-generated point-clouds, which are naturally much bigger and noisier than the synthetic point-clouds the original test.cpp generates. 

Until now I did the following tests:
case 1) A single kinect-generated point-cloud was fed as two point clouds, the difference being the same random pose difference that the original example introduces. This worked great. The point-cloud were aligned nicely. Note that the same point-cloud was fed (with some small pose difference), so there was 100% overlap between the two point-clouds

case 2) So now I fed two point-clouds with around 20% overlap, but already almost registered (manually in MeshLab). This worked horribly

So, we see that, initial coarse registration doesn't really help as much as the overlap does.

case 3) Now I am thinking, before feeding the point-clouds to ICP,  we can delete the non-overlapping regions from the both the pointclouds, so that the %-overlap would be much much higher. Note that doing ICP with such new point-clouds would still result in the same R,T output. So, we would get the same output conservatively. The advantage is two-fold: smaller input point-clouds means faster ICP and higher-%-overlap means much more accurate answer.

As expected, This worked better: much much more accurate answer, plus, much faster :)

Note that though the point clouds had more %-overlap they were NOT coarsely registered already as we had in case(2), that makes it little harder. So if we had an initial coarse pose estimate, then I believe we should get awesome results. 
So let's do that-
Now, we will not only keep just the overlapped parts of the point cloud, but keep them coarsely aligned. That would be our case (4).

case 4) Shockingly and sadly, it went horrible x-( .... I should try it again !!!!

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