How to use DagMC for ray casting:

The ray_fire_test is a good example of how to use DagMC for ray casting.
1) DagMC::load_file
  If using a solid model, ReadCGM will facet the model using CGM. If using a mesh 
  model, DagMC expects the same geometric topology and senses as created by ReadCGM.
2) DagMC::init_obb_tree
  The implicit complement is created, which adds an implicit volume to all surfaces 
  adjacent to only one volume. An oriented bounding box tree is built to accelerate 
  intersection searches. 
3) DagMC::ray_fire
  Given a ray origin and direction, perform the ray cast. 
