checksum or hash-table bucket distributions). Real hashes should normally give very different results for small changes in the input (e.g. IMO the word "hash" is a bit misleading here as it has not much in common with real hashes. The papers talks about geometrically hashed lookup. So this is where the real magic happens IMO. So we have a triangle and want to know if a similar triangle exists anywhere in the selected index.
#THEIA ASTROMETRY CODE#
Maybe they should have better named them "Asterism" (the code has a lot of very bad naming, as we soon will discover, took me hours to figure out). But by my own experiments they seem to be just triangles. The cited paper always talks about 4 stars that form a quad. Now the algorithm goes into creating quads. In the end you need a list of coordinates for stars (plus optional flux/intensity/brightness and background). I will not go into details on how does it, just note that you can either use its internal simplexy algorithm or use SExtractor. As others already pointed out, the main input to the whole process is a list of stars. I've been trying to figure out the technical details of for quite some time.
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