[postgis-users] Polygon from a set of points

[Obe, Regina]

Leonardo,

An SRID is mostly useful to say your data is in a specified
coordinate/datum/projection/etc system and therefore since your spatial
reference system is known it can be transformed into another system
using transform etc.  Sometimes the spatial reference system you get
your data in is not the most useful for your analysis, so you transform
to another e.g if you get data in degrees and you do analysis in meters.


Here are a couple of links that may be useful.
http://www.sharpgis.net/2007/05/05/SpatialReferencesCoordinateSystemsPro
jectionsDatumsEllipsoidsConfusing.aspx

These last couple I wrote just because people ask me these questions all
the time.  Let me know if I made any possibly fallacious statements.  I
always feel like a fish out of water so to speak in this area.

http://www.bostongis.com/?content_name=srid#82

http://www.bostongis.com/postgis_geomfromtext.snippet

http://www.bostongis.com/postgis_pointfromtext_linefromtext_etc.snippet

http://www.bostongis.com/?content_name=postgis_tut03#30 (the section
about transforming to another spatial reference system)

Hope that helps,
Regina
-----Original Message-----
From: postgis-users-bounces at postgis.refractions.net
[mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of
Leonardo Mateo
Sent: Tuesday, June 12, 2007 4:43 PM
To: PostGIS Users Discussion
Subject: Re: [postgis-users] Polygon from a set of points

On 6/12/07, Kevin Neufeld <kneufeld at refractions.net> wrote:
> I see. Yes, it's certainly possible. Since you are coming straight
from
> text, I think the easiest for you would be to use geomfromtext()
method.
>
> SELECT GeomFromText('POLYGON((-67.84208673890122 -31.89216012405324,
> -67.84097873325344 -31.8878559482676, ...))');
>
> Note: you can optionally add the SRID of the projection you are in as
a
> second parameter if you plan on performing any projection operations.
>
> Is that what you were after?
Thanx!!! That was exactly what I was after. By the way, sorry for the
cross posting, but I don't quite understand the what the SRID is for.
PostGIS docs are not really useful on this topic. Do you know some URL
or something where I can read about? Or maybe I should start another
thread for this?

Thanx a lot for your time, and sorry for the very basic questions.


-- 
Leonardo Mateo.
There's no place like ~
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