How do I compare RNA structures?

Question

[dooley]

I have ~700 RNA structures that were generated using Unifold. I can visually go through and say "yep these two are the same" but how do I do that programmatically? Is there a way to take a structure and "3d BLAST" it (eg if oriented the same direction structure 1 and 2 are 98% similar)? I don't want nucleotide similarity because it is the structure that matters not the sequence. Different sequences could make the same structure.