Fast geometric hashing for automated astrometry

Friday 20 February 2009This is more than 14 years old. Be careful.

Fast Geometric Hashing for Automated Astrometry is a fascinating presentation about a solution to the problem of examining a photo of a section of the sky, and figuring out what part of the sky it is. It involves geometry, and algorithms, a clever hashing algorithm for that returns the same result independent of rotation and scale, mapping, search trees, and so on.

I’m not much of an astronomer: I didn’t realize for example, that the catalog of the sky included roughly a billion objects! I’d never heard of HEALPix, a scheme for dividing spheres into uniform grids (pixelizing them). And kd-trees are a data structure for dividing up space, kind of like a 3D tree map.

Plenty of goodies for nerds of all sorts.

PS: the whole thing has been hooked up with the flickr API to automatically identify objects in astronomy pictures on flickr. Very cool.


Ned, thanks for this great link! I was staring at a photograph of the sky recently that I had taken somewhere out West, and after several minutes gave up trying to figure out which patch of sky it was. Now I know where to go to find a match.

I guess I can't really incorporate this into PyEphem because it doesn't do image processing. Too bad. :-)

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