Geohash: text representation allows you to sort locations by proximity

http://en.wikipedia.org/wiki/Geohash

by ncw96 • 12 years ago

39 8 12 years ago

en.wikipedia.org

namplaa• 12 years ago

When the prefix (or infix) doesn't match for something that is close it looks like the prefixes are simply inverted. So 10000 and 01111 are obviously close. I haven't verified.

e98cuenc• 12 years ago

There is another free library to do that, among other things, by Google. It's not well known, but it was used all over the place internally (at least by the geo team).

https://code.google.com/p/s2-geometry-library/

The key difference with geohash is that it uses a Hilbert curve instead of a z-curve and it projects the world in a cube instead of using directly cartesian coordinates.

nroets• 12 years ago

It only attempts to "allow you to sort locations by proximity", as explained in the article.

qwerta• 12 years ago

If you like this stuff, have a look at Healpix: http://healpix.sourceforge.net/ It splits sphere into pixels each with separate number. It is sort of fast hashing for spherical purposes in astronomy. It does not require trigonometric operations and is very fast.

ushi• 12 years ago

Ruby implementation: https://github.com/davetroy/geohash

jamra• 12 years ago

Why would you link this?

It wraps around a java jar file. I can't study the code to see how it's implemented.

hydrozen• 12 years ago

I believe by default it uses the C implementation which you can read here: https://github.com/davetroy/geohash/blob/master/ext/geohash_...

EGreg• 12 years ago

Or to get rid of fault lines you can store two geohashes - the second one shifted so between the two, you can find many more "near points".

That said, geohashes like this are bad because they rely on lat/long without normalizing for distance first

Geohash: text representation allows you to sort locations by proximity

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