AutoCAD Civil 3D

[#1]

I know that there is a limitation on the numbers of points added to a surface from a point cloud.  But I'm curious how Civil 3D determines which points to exclude from the surface.  Is there a special alorithm/criteria the software uses?

[#2]

It's based on the Point Cloud Style Classification and the Point Density setting.  If all points are selected in the Classification, it will use all points.  Typically you will want to uncheck all the vegetation point, building, etc. and only have the Ground classification selected when creating your surface.

The surface will update based on the Point Cloud Style and Density.  So it is a dynamic surface related to the point cloud display.  So if you want to keep your surface with just a select number of points but still display other points from the point cloud, then you will want to create a snap shot before doing so.

Hope this helps.