CloudCompare forum

Hi Daniel, congratulations for your CC software. Can i ask you a few questions about M3C2, as discribed in the page http://www.cloudcompare.org/doc/wiki/in ... 2_(plugin)?:
a) "Multi-scale: for each core points, normals are computed at several scale and the most 'flat' is used " -> what is the meaning of 'flat': the value of D that is chosen is the one that produces the minimum standard deviation in the plan computation?
b) supose i chose the default option in the Computation mode; which option can i chose in the Orientation and what that it mean?
c) in the example shown in M3C2 page, when discribing the Main params, what are the units of the Normals, Projection and max depth? The same as the units of the original point cloud (normally in m, i supose)? The values shown are quite large: for example, subsample cloud#1=122,130000=min distance between point.
d) when i click twice in the guess params, the values vary a little bit. Does that influence the results?

Thank you very much for your work and for sharing it.

Hi,

Dimitri Lague (the author of the M3C2 algorithm) would answer better than me ;)

a) I guess you are right
b) the orientation is a hint that you give to the algorithm so as to be able to orient the normals in the right direction (i.e. pointing outside of the real surface)
c) the units are not necessarily in meters. It depends on the actual units of your clouds. CC loads the coordinates as they are stored in the file. Most of the file formats don't give any information about the units. Therefore the user should know better than CC what are the units. And in your case I guess it's more likely to be millimeters (but you'll have to check this yourself, either with the scale that appears in the bottom right part of the screen or with the point picking tool)
d) the 'guess params' tool do some random sampling on the point clouds to guess acceptable parameters. Of course if they change the result might change a little bit (but this shouldn't change anything in a 'statistical' point of view). And beware that the parameters guessed by the plugin can't be as reliable as the ones you will set yourself (as you should have more information about the clouds and what you are looking for than the plugin ;).