How align(register) and merge point clouds to get full 3d model?

Question

I want to get 3d model of some real word object. I have two web cams and using openCV and SBM for stereo correspondence I get point cloud of the scene, and filtering through z I can get point cloud only of object. I know that ICP is good for this purprose, but it needs point clouds to be initally good aligned, so it is combined with SAC to achieve better results. But my SAC fitness score it too big smth like 70 or 40, also ICP doesn't give good results.

My questions are: Is it ok for ICP if I just rotate the object infront of cameras for obtaining point clouds? What angle of rotation must be to achieve good results? Or maybe there are better way of taking pictures of the object for getting 3d model? Is it ok if my point clouds will have some holes? What is maximal acceptable fitness score of SAC for good ICP, and what is maximal fitness score of good ICP?

Example of my point cloud files: https://drive.google.com/file/d/0B1VdSoFbwNShcmo4ZUhPWjZHWG8/view?usp=sharing

Answer 1

My advice and experience is that you already have rgb images or grey. ICP is an good application for optimising the point cloud, but has some troubles aligning them.

First start with rgb odometry (through feature points aligning the point cloud (rotated from each other)) then use and learn how ICP works with the already mentioned point cloud library. Let rgb features giving you a prediction and then use ICP to optimize that when possible.

When this application works think about good fitness score calculation. If that all works use the trunk version of ICP and optimize the parameter. After this all been done You have code that is not only fast, but also with the a low error of going wrong.

The following post is explain what went wrong.

Using ICP, we refine this transformation using only geometric information. However, here ICP decreases the precision. What happens is that ICP tries to match as many corresponding points as it can. Here the background behind the screen has more points that the screen itself on the two scans. ICP will then align the clouds to maximize the correspondences on the background. The screen is then misaligned
https://github.com/introlab/rtabmap/wiki/ICP