RLE sparse level sets

The RLE sparse level set representation has many beneficial characteristics: (1) highly scalable, (2) fast to access randomly, (3) sequential traversal of the narrow band is optimal, (4) approximate distance values are provided throughout the bounding volume, and (5) easily adapted to work with the large majority of existing level set methods developed for regular grid structures. These advantages are not all shared by the octree, the sparse field method, or the sparse block grid scalable level set representations (reviewed in [Bridson 2003].)