[mapserver-dev] Re: problem with WFS DWithin

[Yewondwossen Assefa]

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
>>  >>  >
>>  >>  >
>>  >>  >
>>  >>  >
>>  >>
>>  >>
>>  >>
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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
>>  ----------------------------------------------------------------
>>
>>
> 
> 


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

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

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