Can Point Cloud data be clipped and converted into a DGN file? / Best method for creating a surface


I have a large point cloud area, but I only require a small section. The file is currently too large to work with.

Can I crop the desired area and create either a new *pod or DGN file?

Also, what is the best method of creating a surface/mesh?

The area is a railway line with an over bridge & general  railway infrastructure e.g. gantries, signals, etc.