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Posted to dev@lucene.apache.org by "Erick Erickson (JIRA)" <ji...@apache.org> on 2013/11/30 15:10:36 UTC
[jira] [Reopened] (LUCENE-1815) Geohash encode/decode floating
point problems
[ https://issues.apache.org/jira/browse/LUCENE-1815?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Erick Erickson reopened LUCENE-1815:
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> Geohash encode/decode floating point problems
> ---------------------------------------------
>
> Key: LUCENE-1815
> URL: https://issues.apache.org/jira/browse/LUCENE-1815
> Project: Lucene - Core
> Issue Type: Bug
> Components: modules/spatial
> Affects Versions: 2.9
> Reporter: Wouter Heijke
> Priority: Minor
>
> i'm finding the Geohash support in the spatial package to be rather unreliable.
> Here is the outcome of a test that encodes/decodes the same lat/lon and geohash a few times.
> the format:
> action geohash=(latitude, longitude)
> the result:
> encode u173zq37x014=(52.3738007,4.8909347)
> decode u173zq37x014=(52.373799999999996,4.890934)
> encode u173zq37rpbw=(52.373799999999996,4.890934)
> decode u173zq37rpbw=(52.373799999999996,4.8909329999999995)
> encode u173zq37qzzy=(52.373799999999996,4.8909329999999995)
> if I now change to the google code implementation:
> encode u173zq37x014=(52.3738007,4.8909347)
> decode u173zq37x014=(52.37380061298609,4.890934377908707)
> encode u173zq37x014=(52.37380061298609,4.890934377908707)
> decode u173zq37x014=(52.37380061298609,4.890934377908707)
> encode u173zq37x014=(52.37380061298609,4.890934377908707)
> Note the differences between the geohashes in both situations and the lat/lon's!
> Now things get worse if you work on low-precision geohashes:
> decode u173=(52.0,4.0)
> encode u14zg429yy84=(52.0,4.0)
> decode u14zg429yy84=(52.0,3.999999)
> encode u14zg429ywx6=(52.0,3.999999)
> and google:
> decode u173=(52.20703125,4.5703125)
> encode u17300000000=(52.20703125,4.5703125)
> decode u17300000000=(52.20703125,4.5703125)
> encode u17300000000=(52.20703125,4.5703125)
> We are using geohashes extensively and will now use the google code version unfortunately.
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