How to determine the location of the cell center
 

Hi

My code being developed uses .msh mesh files from gambit, Icem etc. My problem is how to determine the location of the cell grid points if all the faces are given. I think its favourable if

-the grid points are in the centroid, (variable value in centroid represents better the average value within the cell)

- and if face centers are on the lines connecting the neighbouring grid points. (more accurate interpolating)

But how to do that in case 3d unstructured grid, or in case of a 2d triangle cell? (its easy in case of a square cell). I found that its impossible to statisfy both, or the second one. What do you suggest to determine the loc. of grid points within the cells? Should i use the centroid? if i should, how to determine where is the centroid in case of a 3d cell?
(with numerical integration for each cell? Doesnt it require to much additional calculation?)
thank you
regards
Zoli