[postgis-users] boundary or envelope of cloud of points

[nicklas.aven at jordogskog.no]

Hallo 
 
you can read about it here:
http://www.postgis.org/documentation/manual-svn/ST_ConvexHull.html
ST_ConvexHull will give you a better result but as you see in the documentation there is no function that gives a concave hull as you have in your example link.
 
/Nicklas
 


2009-02-12 My Pid wrote:

Hello,
>
>I am really a newbie in the postgis world.
>
>I am a developper for http://www.openbmap.org/ website
>which identify GSM cell area from measures of GSM data
>and GPS coordinates.
>
>So I am planning to go from mysql to postgresql/postgis
>and I am looking for a function that does the following:
>
>I have a table containing the gps coordinates mentionned above.
>I would like to generate a enveloppe or a boundary of the area
> of the GSM cell.
>
>What I have tried (among others)
>
>SELECT ST_AsText(ST_Envelope(ST_Collect(gps_coordinates))) FROM "208_1_14592_gps";
>
>with gps_coordinates - POINT geometry
>
>It seems to output a 4 points polygons and I would like to get something like
>
>http://realtimeblog.free.fr/cell_map.php?mcc=208&mnc=1&lac=14592&cellid=62403&display=Display
>
>
>
>Is it possible to use postgis functions to generate this kind of envelope ?
>
>regards,
>Nick
>
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