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<div>I am not sure I understand what you want to do. Do you want one sqare-polygon for each point? </div>
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<div>Now you are unioning them all together to one big polygon....</div>
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<div>anyway</div>
<div>instead of :</div>
<div>envelope(buffer(geom,1.0/230.0)) </div>
<div>I guess it's more effective to use:</div>
<div>st_expand(geom, 1.0/230.0)</div>
<div> </div>
<div><a href="http://www.postgis.org/documentation/manual-svn/ST_Expand.html">http://www.postgis.org/documentation/manual-svn/ST_Expand.html</a></div>
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<div> </div>
<div>/Nicklas</div>
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<div><br />
2009-06-19 pcreso@pcreso.com wrote:<br />
<br />
<br />
>Hi,<br />
><br />
>Any comments or advice appreciated...<br />
><br />
>I have a table (155m points) of circumpolar depth points.<br />
><br />
>From this I want to use POstGIS to generate polygons based on depths.<br />
><br />
>There are about 700,000 points in the Ross Sea region, each has a depth (or altitude) associated with it. The points are 1/2nm apart (GEBCO 2008 data)<br />
><br />
>I figure the following approach will work to generate reasonable polygons for areas in the Ross Sea shallower than 550m:<br />
><br />
>select astext(geomunion(envelope(buffer(geom,1.0/230.0))))<br />
> from srtm_ant<br />
> where depth <0<br />
> and depth >-500<br />
> and geom && setsrid(geometryfromtext('POLYGON((155 -80,155 -60,200 -60,200 -80,155 -80))'),4326);<br />
><br />
><br />
>The && WKT coords define the Ross Sea region, 1/2nm is 1/120 degree so a buffer of 1/230 degree should ensure the envelopes of the buffered points all overlap.<br />
><br />
><br />
>Does anyone have any suggestions/advice regarding this?<br />
><br />
>Better or faster approaches, etc.<br />
><br />
><br />
>Thanks,<br />
><br />
> Brent Wood<br />
>_______________________________________________<br />
>postgis-users mailing list<br />
>postgis-users@postgis.refractions.net<br />
>http://postgis.refractions.net/mailman/listinfo/postgis-users<br />
><br />
></div>
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