Finds the volume under a 3D surface above and below a reference Z value. If the reference Z value is above the surface, the calculated "above" volume is negative.
For this surface:
By default this operation will consider the entire surface. If "Consider entire surface" is unchecked, you may specify the X and Y extents within which the volume will be calculated. This might be useful for surfaces containing multiple peaks, where you want the volume under only one of those peaks. Please note: Triangles with one or more vertices outside those extents will be ignored.