[mapserver-dev] Re: problem with WFS DWithin

[Yewondwossen Assefa]

Hi There,

It is implemented using geos within functionality where the query shape 
is a buffered copy of the original shape.  Same for within.
My interpretation of the within/dwithin  operator looking at the specs 
"simple feature specification for sql" was that the feature should be 
totally contained. If that is not the case, It can easily be changes to 
use the distance geos operator.

Best Regards

Paul Ramsey wrote:
> DWIthin(A, B, D)
> 
> should be functionally identical to
> 
> Distance(A, B) < D
> 
> so no, what you describe doesn't sound like a correct DWithin, Bart.
> BTW, if it's implemented as
> 
> Intersects(A, Buffer(B, D))
> 
> it's incredibly inefficient.
> 
> P.
> 
> On Thu, Mar 27, 2008 at 8:19 AM, Bart van den Eijnden (OSGIS)
> <bartvde at osgis.nl> wrote:
>> Okay, it seems it only returns features if they are totally contained within
>>  the searchshape + distance (the buffered linestring).
>>
>>  Is this the way DWithin is supposed to behave? I am not a geometry operator
>>  specialist unfortunately, but my expectation was to get any of the polygons
>>  containing the buffered linestring.
>>
>>  A small buffer (500 m) selects nothing:
>>  http://www.osgis.nl/download/umn/dwithin1.png
>>
>>  A bigger buffer (2500 m) only selects 3 polygons:
>>  http://www.osgis.nl/download/umn/dwithin2.png
>>
>>  Best regards,
>>  Bart
>>
>>  --
>>  Bart van den Eijnden
>>  OSGIS, Open Source GIS
>>  http://www.osgis.nl
>>
>>
>>  --------- Oorspronkelijk bericht --------
>>  Van: Bart van den Eijnden OSGIS <bartvde at osgis.nl>
>>  Naar: mapserver-dev at lists.osgeo.org <mapserver-dev at lists.osgeo.org>
>>  Onderwerp: problem with WFS DWithin
>>  Datum: 27/03/08 14:59
>>
>>  >
>>  > Hi list,
>>  >
>>  > I can't get a DWithin filter containing a LineString to work. I am using a
>>  > polygon layer. It doesn't select anything. Using 5.0.2.
>>  >
>>  > A DWithin containing a Polygon works fine.
>>  >
>>  > Any ideas what could be causing this?
>>  >
>>  > Did anybody else experience the same thing?
>>  >
>>  > Best regards,
>>  > Bart
>>  >
>>  > --
>>  > Bart van den Eijnden
>>  > OSGIS, Open Source GIS
>>  > http://www.osgis.nl
>>  >
>>  >
>>  >
>>  >
>>
>>
>>
>>  _______________________________________________
>>  mapserver-dev mailing list
>>  mapserver-dev at lists.osgeo.org
>>  http://lists.osgeo.org/mailman/listinfo/mapserver-dev
>>
> _______________________________________________
> mapserver-dev mailing list
> mapserver-dev at lists.osgeo.org
> http://lists.osgeo.org/mailman/listinfo/mapserver-dev
> 
> 


-- 
----------------------------------------------------------------
Assefa Yewondwossen
Software Analyst

Email: assefa at dmsolutions.ca
http://www.dmsolutions.ca/

Phone: (613) 565-5056 (ext 14)
Fax:   (613) 565-0925
----------------------------------------------------------------