struct GRIDCELL {
   Vec3f p[8];		//position of each corner of the grid in world space
   float val[8];	//value of the function at this grid corner
};

//given a grid cell, returns the set of triangles that approximates the region where val == 0.
int Polygonise(GRIDCELL &Grid, TriMeshFace *Triangles, int &NewVertexCount, Vec3f *Vertices);