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From "Chuck Williams" <ch...@manawiz.com>
Subject RE: GIS
Date Sun, 31 Oct 2004 17:40:39 GMT
I for one would love to have this functionality, i.e. would use it
immediately if available and efficient.  It seems the biggest problem is
how you are going to index the information.  If you store and index the
latitude and longitude for a geographically-positioned document, and
then want to find all such documents with a spherical rectangle or
circle, how do you find the candidates?  As far as I know, Lucene does
range searches now by expanding a range into a list of all possible
values within that range.  This is clearly not a reasonable approach for
latitudes and longitudes, assuming you need precision on the values
(which I do).  There are potentially reasonable indexing approaches that
occur to me (e.g. in addition to precise lat/lon store with each object
its grid label in a few different discrete lat/lon grids, or use a
b-tree index of some kind), but this is probably a solved problem
somewhere in the field of geographical information systems.

After the indexing, the next interesting question would seem to be the
scoring, although this seems a much simpler issue.  E.g., a score
related to the distance from the center of the query region would seem
to be appropriate.  There should be a mechanism analogous to the current
coord so that this could be tuned or turned off, depending on the needs
of particular queries within the application.

My $0.02,

Chuck

  > -----Original Message-----
  > From: Guillermo Payet [mailto:gpayet@localharvest.org]
  > Sent: Sunday, October 31, 2004 9:34 AM
  > To: lucene-dev@jakarta.apache.org
  > Cc: scoob@mindinmotiontech.com
  > Subject: GIS
  > 
  > Hello,
  > 
  > I'm new here, so first of all I'd like to say hello to everyone.
  > 
  > So, hi there...
  > 
  > I just spent two days trying to get Lucene to handle "geographically
  > constricted" searches for our website. (Check out
www.localharvest.org)
  > 
  > I got close, but no cigar. (it works, but is very slow)
  > 
  > We need to be able to do searches only within a geographicaly
limited
  > set of documents.  (In this case, our member listings)
  > 
  > So... I'd like to volunteer to add the needed functions in Lucene
  > to:
  > 
  >   - build a LatLonField class for geographical coordinates
  >   - build a LatLonRectTerm (or whatever) to define matches
  >     within a latitude/longituded defined rectangle.
  >   - build a LatLonRadiusTerm (or whatever) to define all matches
  >     within X distance from a point (lat,lon).
  > 
  > We're now doing all of this through MySQL, which works "ok", but
leaves
  > a lot to be desired for the relevance of search results for a lot of
  > searches.  I've already written all the spherical trig functions to
  > to do these searches accurately, and I'd love to port them into
  > Lucene.
  > 
  > So my questions are:
  > 
  >  - Has there been any talk about doing this before?
  >  - Is this a bad idea for any reason?
  >  - What would be the right approach to do this?
  > 
  > The fact that Lucene stores and indexes (or seems it seems) all
terms
  > as Strings and that there is no NumericTerm makes me think that I
  > might be missing something and that this migh be a much bigger deal
  > than I think?
  > 
  > 	--G
  > 
  > 
  > 
  > 
  > --
  > Guillermo Payet
  > L O C A L  H A R V E S T
  > http://www.localharvest.org
  > 
  > Every Morning I awake torn between a desire to save the world and
  > an inclination to savor it.  This makes it hard to plan the day.
  > 
  >                                                        -E.B.White
  > 
  > 
  >
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