Surface entity definitions consist of group codes that are common to all surface types, followed by codes specific to the type.
Common Surface group codes
Group code
Description
100
Subclass marker (AcDbModelerGeometry)
70
Modeler format version number (currently = 1)
1
Proprietary data (multiple lines < 255 characters each)
3
Additional lines of proprietary data (if previous group 1 string is greater than 255 characters) (optional)
Subclass markar (AcDbSurface)
71
Number of U isolines
72
Number of V isolines
