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Hallo<br>
<br>
What you do is htat you use the linestrings defining the polygons
instead of the polygon instead in the ST_Dwithin statement.<br>
<br>
Then you can also us ST_Closestpoint to find a line between the
point and the closest point on the edge. This line can you use in
ST_Azimuth.<br>
<br>
If your polygons have inner rings you can use ST_DumpRings to take
also those in account. If you only want to use the exterior rings
you can omit that part. But if there is multipolygons, you should
use ST_Dump instead just to get single polygons.<br>
<br>
<br>
<br>
SELECT ST_Azimuth(point_table.the_geom,
ST_ClosestPoint(edges.the_geom, point_table.the_geom)) as
the_azimuth FROM<br>
(SELECT ST_ExteriorRing((ST_DumpRings(the_geom)).geom) as the_geom
FROM polygons_table) edges<br>
, point_table<br>
WHERE ST_DWithin(edges.the_geom, point_table.the_geom, 10000);<br>
<br>
<br>
HTH<br>
<br>
Nicklas<br>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
On 02/16/2012 04:53 PM, uk52rob wrote:
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<p class="MsoNormal">Hi,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I need to create a WHERE statement which is
true if a point is within 10000 metres of the closest edge of
a polygon (EPSG:27700).<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I have this working fine for point to point
queries, but I am struggling with point to polygon. I also
need to perform ST_Azimuth on the resulting data to return a
bearing.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Has anyone got any ideas? <o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Thanks<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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<br>
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