In AutoCAD Civil 3D you can build, edit, and save large surfaces. The term “large surface” applies to a surface with a number of points exceeding one million (generally, 1 million points for a grid surface or a snapshot of a TIN surface, and 2 million points for a TIN surface).
AutoCAD Civil 3D has a mechanism for handling operations with large surfaces. When you save a drawing containing a large surface, the data pertaining to the large surface is written to a separate file that is saved in the same location where the surface drawing resides. The TIN surface companion files have the .mms file extension, and the grid surface files have the .grs file extension. The file name of a surface companion file has the <drawing_name>_<surface object handle>.mms format.
For more details on working with large surfaces, see:
