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

[My Pid]

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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