Calculates the 2nd moment of volume (SMV) by multiplying the volume of each triangle in the mesh by its centroids' distance from the origin (should be set to the attachment point of the mesh). The sum of these values is the 2nd moment of volume. Axis is z by default, meaning it will calculate the vertical second moment, but this can be changed if needed. This metric is size-dependent so to compare moments in terms of shape only, set scale = TRUE.