# [Chimera-users] Question about Measure Volume and Area

Thomas Goddard goddard at cgl.ucsf.edu
Mon Aug 18 10:35:12 PDT 2008

```Hi Patrick,

The calculation of volume enclosed in the triangulated surface is
trivial.  I just choose any point (say the first vertex of the surface),
then sum up the volumes of the tetrahedrons formed by that point and
each triangle face making up the surface.  (Some of those tetrahedrons
are inverted and have negative volume.)  This gives the exact volume
enclosed in the surface which is defined by triangles.  One small catch
is that I need to check that the surface has no holes since then the
volume is not well-defined.  For a solvent excluded surface there will
be no holes.

Tom

Patrick Redmill wrote:
> Hey guys,
>    One more quick question. Is there a non-trivial calculation
> associated with the surface enclosed volume? Or is it just a numerical
> integration between the surfaces? If it's non-trivial, is there a good
> ref for the algorithm? Thanks!
>
> ~Patrick
>

```