Points cloud fill gap

Questions & Answers
1

General Information

  • Product: N46-602-16-BL

I’m using Ensenso to acquire points cloud of a surface with some holes at about 1500mm.
The holes have about 30mm diameter.
I using PatchMatch stereo matching. In many cases the holes are filled with points or the hole is very smaller than it is in reality. I improved the reconstruction by setting the windowradius value to 0 instead of automatic, but I’m worried that this can be happen again.

How can I fix that?!

2

Hi,

PatchMatch propagates information from the neighbouring pixels and indeed tends to smooth over small holes by default.

The most important parameters to prevent this are the following:

  • Smoothness should be set manually and to a relatively low value to reduce propagation of information between pixels.
  • UniquenessRatio can be used to filter out pixels where information was still propagated into the holes. For this case you probably want to set it to a very high value. Try around 90 as a starting point.
  • It might also help to reduce ShadowingThreshold to 1.

I hope this helps. It can be quite tricky to get good holes without removing too much valid information in other places.

3

Hello Daniel, Thanks for the answer,
I know uniqueness ratio could be usefull in this scenario, but unfortunatelly I also need to acquire other little details.
Shadowing threshold helped, but with high value.
I’ll try to lower smoothness value, it’s set on automatic right now.

However it’s really strange that such holes are filled with points with post processing. They are not small at all.

4

Hi Michele,

we know about this effect of the PatchMatch stereo matcher, and there is an update coming with the release of SDK 4.1 around the end of November, which will combine the advantages of the Correlation stereo matcher with PatchMatch.

Meanwhile you can try to use Correlation as stereo matching method, probably with WindowRadius 1, and some CorrespondanceThreshold which filters the point cloud by correlation coefficient. This should give you a much better representation of the holes. The drawback is for now, that you have limited matching range, compared to PatchMatch.

Best regards, Rainer