API : How can I detect a ray intersection with a mesh or face?

1. http://help.autodesk.com/view/MAYAUL/2017/ENU/?guid=__py_ref_class_open_maya_1_1_m_fn_mesh_html

MFnMesh.closestIntersection

Note, I'e been unable to get this to work via maya.OpenMaya, but I have got it to work via maya.api.OpenMaya
Also note the points it reruns are always in internal units (cm) so you may need to convert them to your UI units.