centroid expression function
Returns centroid information for a surface node.
Replaced by: hou.Geometry
The type should be one of
D_Z for the corresponding components of the centroid.
centroid("../sphere1", D_X) centroid("../sphere1", D_Y) centroid("../sphere1", D_Z)
The centroid is the center of the bounding box of the points, not the average position of the points.