Hallo
What you do is htat you use the linestrings defining the polygons
instead of the polygon instead in the ST_Dwithin statement.
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.
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.
SELECT ST_Azimuth(point_table.the_geom, ST_ClosestPoint(edges.the_geom,
point_table.the_geom)) as the_azimuth FROM
(SELECT ST_ExteriorRing((ST_DumpRings(the_geom)).geom) as the_geom FROM
polygons_table) edges
, point_table
WHERE ST_DWithin(edges.the_geom, point_table.the_geom, 10000);
HTH
Nicklas
On 02/16/2012 04:53 PM, uk52rob wrote:
Hi,
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).
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.
Has anyone got any ideas?
Thanks
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