I have done some extensive debugging in my code and came to the
conclusion that rt_shootray randomly misses if the point of origin is
very close to the surface.
Can somebody confirm this behaviour? If it is to be expected, I could
write a workaround which offsets the origin a little bit in one
direction. It would be good to know what are the tolerances for the ray
tracing in BRL-CAD; are the absolute or relative to a biggest length or