### Implement a centroid function for N-faced polysolids (ARBN)

**completed by**: Johannes Schulte

**mentors**: Sean

BRL-CAD provides more than two dozen types of geometry ''primitives'' such as ellipsoids, boxes, and cones. Every primitive is described by a collection of callback functions, for example rt_ell_bbox() returns the bounding box dimensions for an ellipsoid. Wikipedia, Wolfram Mathworld, and various other math sites (and research papers) around the web include the equations for most of our basic primitives while others are a little more tricky to compute.

References:

- http://en.wikipedia.org/wiki/Centroid
- http://mathworld.wolfram.com/
- include/raytrace.h: See ft_centroid callback defined in the rt_functab structure

Code:

- src/librt/primitives/arbn/arbn.c (implement your function here)
- src/librt/primitives/table.c (add a reference to your function here)

This task involves writing a new callback function that takes an rt_db_internal object and calculates its centroid (as a point_t 3D point). There are numerous examples in our code where we compute centroids for other primtiives. Submit a patch file the may be applied cleanly.

If you succeed, a follow-on task may be created to enable and validate your function.