[mapserver-dev] Re: problem with WFS DWithin

[Paul Ramsey]

Assefa,

I can't see DWithin in SFSQL.

In OGC Filter, the "definition" is useless!  "The spatial operators
DWithin and Beyond test whether the value of a geometric property is
within or beyond a specified distance of the specified literal
geometric value."

The Javadoc from GeoAPI is clear and fits my personal understanding:
http://geoapi.sourceforge.net/2.0/javadoc/org/opengis/filter/spatial/DWithin.html

There is surprisingly little clarity in the stuff I netted from
Google. When I get home to my SQL/MM file I'll see if ISO is clearer.

Paul


On Thu, Mar 27, 2008 at 9:07 AM, Yewondwossen Assefa
<yassefa at dmsolutions.ca> wrote:
> 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
>  >>  >
>  >>  >
>  >>  >
>  >>  >
>  >>
>  >>
>  >>
>  >>  _______________________________________________
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>  >>  http://lists.osgeo.org/mailman/listinfo/mapserver-dev
>  >>
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>
>  --
>  ----------------------------------------------------------------
>  Assefa Yewondwossen
>  Software Analyst
>
>  Email: assefa at dmsolutions.ca
>  http://www.dmsolutions.ca/
>
>  Phone: (613) 565-5056 (ext 14)
>  Fax:   (613) 565-0925
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>