[mapserver-dev] Re: problem with WFS DWithin
Yewondwossen Assefa
yassefa at dmsolutions.ca
Thu Mar 27 18:00:31 EDT 2008
Paul,
I have opened a ticket on this
http://trac.osgeo.org/mapserver/ticket/2564.
Also note that we had this similar discussion on DWithin and Beyond
in bug http://trac.osgeo.org/mapserver/ticket/2105#comment:6
Best Regards,
Paul Ramsey wrote:
> Ok, one last kick:
>
> "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."
>
> If we use Assefa's definition, then there is a case missing... an
> object is either DWithin, DBeyond, or DOnTheLine. If we use the
> GeoAPI definition, then the Within/Beyond duality is complete: an
> object is either within or beyond, there is no third state.
>
> P.
>
> On Thu, Mar 27, 2008 at 1:04 PM, Paul Ramsey <pramsey at cleverelephant.ca> wrote:
>> SQL/MM is not helpful, there's no DWithin in the draft I have
>> available. All I have left is to appeal to Oracle's
>> SDO.WITHIN_DISTANCE and note that it also shares the GeoAPI
>> definition: http://download.oracle.com/docs/html/A85337_01/sdo_objg.htm#854615
>>
>> Whether WITHIN_DISTANCE is semantically equivalent to DWITHIN is left
>> as an exercise for the pub after work.
>>
>> P.
>>
>> On Thu, Mar 27, 2008 at 11:23 AM, Yewondwossen Assefa
>>
>>
>> <yassefa at dmsolutions.ca> wrote:
>> > Paul Ramsey wrote:
>> > > Assefa,
>> > >
>> > > I can't see DWithin in SFSQL.
>> > >
>> > You are right. Within is defined in SFSQL. I meant that I interpreted
>> > DWithin using the same definition as Within.
>> >
>> >
>> > > 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."
>> > >
>> > True :)
>> >
>> >
>> > > 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.
>> > >
>> >
>> > If there is some clear definition/consensus on this, I see no problem
>> > changing it to fit the GeoAPI way, although I think Within and DWithin
>> > should behave similarly.
>> >
>> > Best Regards,
>> >
>> >
>> >
>> > > 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
>> > >> >> >
>> > >> >> >
>> > >> >> >
>> > >> >> >
>> > >> >>
>> > >> >>
>> > >> >>
>> > >> >> _______________________________________________
>> > >> >> 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
>> > >> ----------------------------------------------------------------
>> > >>
>> > >>
>> > >
>> > >
>> >
>> >
>> > --
>> >
>> >
>> > ----------------------------------------------------------------
>> > 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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>
--
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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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