I propose to add VolumeCenterX, VolumeCenterY and VolumeCenterZ to vtkMassProperties.
These properties are easy to calculate as follows:
for each triangle:
create a tetrahedron for the three vertices of this triangle plus the origin as fourth vertex
calculate volume and center of this tetrahedron.
the overall center of mass is then the weighted average of all these centers.
I can add the code to vtkMassProperties.h and vtkMassProperties.cxx
But besides that, what other places do I need to make changes/additions? Test cases, documentation, exposure to python, etc?