[postgis-devel] st_dwithin, st_within, st_dcompletlywithin

nicklas.aven at jordogskog.no nicklas.aven at jordogskog.no
Thu Jul 9 05:32:48 PDT 2009

```I have been looking some more on this Hausdorff Distance. I'm afraid I have to take a step back. There are aspects that is not handled by my original idea and I can't see how to deal with it. The problem I didn't realize is that if the second geometry is "surrounding" the first, we have to search for the most far away point between the vertices. In the ordinary maxdistance-case we don't have to consider that and the maxdistance is always between two vertices.  /Nicklas
2009-07-09 Paragon Corporation wrote:

Oh that's what that is. Hmm and I think its already ported to PostGIS,
>though would be interesting to compare the speeds and results. Since the
>current one in trunk is a GEOS call and Nicklas' would be a native PostGIS.
>
>http://trac.osgeo.org/postgis/ticket/209
>
>Paul are you hmm planning add this to the manual -- I see you closed it? I
>don't recall seeing it in the 1.5 docs or were we waiting for GEOS to be
>patched first?
>
>Thanks,
>Regina
>
>
>-----Original Message-----
>From: postgis-devel-bounces at postgis.refractions.net
>[mailto:postgis-devel-bounces at postgis.refractions.net] On Behalf Of Martin
>Davis
>Sent: Wednesday, July 08, 2009 6:14 PM
>To: PostGIS Development Discussion
>Subject: Re: [postgis-devel] st_dwithin, st_within, st_dcompletlywithin
>
>That distance metric is known as the Hausdorff Distance. It's implemented
>in JTS, and probably in GEOS as well.
>
>nicklas.aven at jordogskog.no wrote:
>>
>>
>> A function that gives the answer to for example:
>> "How far away from France can you get in Belgia"
>> To answer that we have to store compare the shortest distance to
>> geometry2 from each vertex in geometry1 and finaly find wich vertex in
>> geometry1 that has the highest "mindistance" to geometry2.
>> Hope the idee is possible to understand. Is it of any use?
>
>--
>Martin Davis
>Senior Technical Architect
>Refractions Research, Inc.
>(250) 383-3022
>
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