# [Gmsh] Ruled surface interpolation

**Martin Aunskjær**
maaudk at yahoo.dk

*Fri Apr 18 08:05:02 CEST 2008*

Hello,
I've used Gmsh to generate a 3D mesh around a body
made of lots of ruled surfaces. All the triangular
faces on these surfaces receive special treatment in
my fluid dynamics solver, since they must be modified
from being flat to being curved. This procedure
involves projecting a lot of Gauss integration points
inside each surface triangle onto the real, curved
surface.
I do this by using the InterpolateSurface() routine in
Geo.cpp. This seems to work fine, except in those
cases where a ruled surface has holes. Say, the
definition is like this:
Ruled Surface(177) = {156, 175};
Then any point inside a surface triangle on surface
177 will be projected onto a surface defined by the
generatrices of edge loop 156, the hole is not taken
into account (holes are skipped in the interpolation
routine). This way, the projected point will in fact
not be on surface 177.
My question is, how can I solve this problem?
The surface meshing routines seems to be capable of
correctly inserting points on ruled surfaces with
holes. Is there some mechanism in the meshing routines
that I can reuse to project my surface triangle
integration points correctly onto any surface ?
Thanks,
Martin
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