CloudCompare mesh adds unwanted surface

[mirt83]

Did you use the 'auto' button of the normals computation dialog? And if the normals are mostly black, then they may be simply globally inverted (use the 'Edit > Normals > Invert' method to invert them).

Hi Daniel, I have a question about inverted normals. I have some noisy clouds, I compute normals but they are inverted. So I use Edit > Normals > Invert' method to invert them: now the normals appears right oriented.
I'm now wondering: why the normals appears well oriented but inverted? Just inverting the normals I resolve the problem?
Thank you

[daniel]

It's because all normals are oriented relatively to their nearest neighbors normals so as to get a consistant look. However, for the very first normal we don't have any information about whether the normal should be in one direction or the other. So you have more or less 50% of chance to get the first normal right, and then all the others will have the same orientation as the first one...