How to determine the object-to-world matrix I want to ray trace a triangular mesh that I load from a file. The vertices' coordinates are expressed in the reference frame associated with the object  (i.e the mesh) and I don't know the object-to-world matrix. Is there a way to calculate this matrix given these coordinates? If no, how can I ensure that the mesh's triangles are transformed to the world's reference frame?
No! If you dont have this info and must have a extra frame, just assume the reference frame is a identity matrix*. The point of the extra reference frame is just to be able to move the object but if you have no info about how the object should relate to other objects it does not really matter operator can move it where they want. Everything is relative, if theres no relation then no problems.

* choosing identity is like choosing a arbitrary constant to be 1, its numerically easy to work with.