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From "Wouter Heijke (JIRA)" <j...@apache.org>
Subject [jira] Commented: (LUCENE-1815) Geohash encode/decode floating point problems
Date Thu, 27 Aug 2009 20:15:59 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-1815?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12748548#action_12748548
] 

Wouter Heijke commented on LUCENE-1815:
---------------------------------------

To me it was major since geohashes are THE way for us to search a location through millions
of records our index has, and small numbers do count! 

I see it this way, if a jpeg picture would not decode like it encoded would you accept it,
also if it would be slightly different?

Right now i don't want to spend my time on finding the cause of the issue since i have working
(google) code and I prefer doing cooler stuff like implementing a solution for the 'greenwich'
geohash problem.

> Geohash encode/decode floating point problems
> ---------------------------------------------
>
>                 Key: LUCENE-1815
>                 URL: https://issues.apache.org/jira/browse/LUCENE-1815
>             Project: Lucene - Java
>          Issue Type: Bug
>          Components: contrib/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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