The file of the surface mesh is in Wavefront .obj format. 

Detail information about .obj format can be found: http://en.wikipedia.org/wiki/Wavefront_.obj_file




The vertices in .obj are written by turn of the cross-sections. For example, when there is 40 points on 
one cross-sectional contour and there are 50 sections on one 3D shape. the vertex in the obj file is:

First 40 points on first cross-sectional contour, 40 points on second cross-sectional contour, 40 points 
on third cross sectional contour, …… 40 points on last (50th) cross-sectional contour.