[postgis-users] how to create a hole in a polygon table?

[Robert Buckley]

Thanks for that...shame it didn´t work.

I have already looked at negative buffers, but they create a polygon within a polygon and not a hole within a "negative-buffered" polyon. i.e my polygon needs to be transparent in the center past the negative buffer so underlying features can be seen.

Andrea Aime thought it could be done with the "Difference" SLD filter, but I can´t seem to get it to work due to my lack of understanding of how the filter works. 

http://docs.geoserver.org/latest/en/user/styling/sld-reference/filters.html 


yours,

Rob






________________________________
 Von: Paul Ramsey <pramsey at opengeo.org>
An: Robert Buckley <robertdbuckley at yahoo.com>; PostGIS Users Discussion <postgis-users at postgis.refractions.net> 
Gesendet: 22:33 Dienstag, 28.Februar 2012
Betreff: Re: [postgis-users] how to create a hole in a polygon table?
 
I was thinking of something like this, but it doesn't work.
Unfortunately Geoserver doesn't have the ability to create offset
lines, so there's no nice way to do this without doing a little
negative buffer on the shape (which incidentally, you could do using
the geometry transformation facility on the fly
http://docs.geoserver.org/stable/en/user/styling/sld-extensions/geometry-transformations.html

P

<?xml version="1.0" encoding="ISO-8859-1"?>
<StyledLayerDescriptor version="1.0.0"
xmlns="http://www.opengis.net/sld"
xmlns:ogc="http://www.opengis.net/ogc"
  xmlns:xlink="http://www.w3.org/1999/xlink"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:gml="http://www.opengis.net/gml"
  xsi:schemaLocation="http://www.opengis.net/sld
http://schemas.opengis.net/sld/1.0.0/StyledLayerDescriptor.xsd">
  <NamedLayer>
    <Name>USA states</Name>
    <UserStyle>      <Name>population</Name>
      <Title>United States</Title>
      <Abstract>A Simple Brush Style</Abstract>
      <FeatureTypeStyle>
       <Rule>
       <LineSymbolizer>
         <Stroke>
         <GraphicStroke>
           <Graphic>
           <ExternalGraphic>
             <OnlineResource xlink:type="simple"
xlink:href="file:///Users/pramsey/green_bottom.gif" />
             <Format>image/gif</Format>
           </ExternalGraphic>
           </Graphic>
          </GraphicStroke>
         <CssParameter name="stroke-linecap">round</CssParameter>
         <CssParameter name="stroke-dasharray">1 0 1 0</CssParameter>
         </Stroke>
       </LineSymbolizer>
     </Rule>
     </FeatureTypeStyle>
    </UserStyle>
    </NamedLayer>
</StyledLayerDescriptor>


On Tue, Feb 28, 2012 at 12:00 PM, Robert Buckley
<robertdbuckley at yahoo.com> wrote:
> Thanks for the advice.
>
> Unfortunately I don´t understand what you have just told me....half-brush?
> half-circle?
>
> are these sld specifications?...I am delivering wms data using sld´s to
> style the data.
>
> could you please clarify?
>
> cheers,
>
> Rob
>
> ________________________________
> Von: Paul Ramsey <pramsey at opengeo.org>
> An: Robert Buckley <robertdbuckley at yahoo.com>; PostGIS Users Discussion
> <postgis-users at postgis.refractions.net>
> Gesendet: 19:20 Dienstag, 28.Februar 2012
> Betreff: Re: [postgis-users] how to create a hole in a polygon table?
>
> Rather than geometry processing, work on your rendering engine. You
> can usually achieve an interior band (the classic National Geographic
> political boundary, yes?) with a half-brush (rather than a full
> circle, use a half-circle), and just ensuring your polygons are
> consistently oriented.
>
> P.
>
> On Tue, Feb 28, 2012 at 10:04 AM, Robert Buckley
> <robertdbuckley at yahoo.com> wrote:
>> Hi,
>>
>> I am trying to create an inner buffer of a polygon geometry table.
>> Unfortunately this is the only way I can think of which will enable me to
>> make a certain symbol for a polyon layer. The SLD Filter "difference"
>> might
>> do it, but it needs to be nested and i´m not sure if this is possible.
>>
>> anyway....My polygons need to be symbolized with a thin outline AND an
>> inside Buffer of 3 mm(150m  at a scale of 1:50 000)....in essence just an
>> inside ring.
>>
>> This means I need to first buffer my polygon geometry and then substract
>> the
>> buffer from the original polygon. = ST_Difference (i think!?!)
>>
>> my attempt created some geometries but not what I was expecting...
>>
>> create view rrop08.rrop_01_13_innerbuffer AS
>>
>> SELECT ST_Difference(a.st_buffer, b.the_geom)
>>
>> FROM rrop08.rrop_01_13_buffer a, rrop08.rrop_01_f b;
>>
>>
>> rrop08.rrop_01_f  = the original polyon
>>
>> rrop08.rrop_01_13_buffer = the inner buffer
>>
>>
>>
>>
>>
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>>
>
>
>
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