<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">Dan,<div><br></div><div>Thanks, that was a really good intro to get my head wrapped around some of the concepts, as this is all new to me.<div><br></div><div>Instead of reprojecting my data, I found that I could use the ST_Transform and ::geography cast to have ST_Area return the geography area instead, a la (snippet follows). This is fine, and performance isn't an issue as I'm working with this data statically. </div><div><br></div><div>select ST_Area(ST_Transform(the_geom,4326)::geography) AS area from ... <snip></div><div><br></div><div>Hope this helps someone else.. </div><div><br></div><div><div>Thanks again!</div></div><div><div><br><div><div>On May 20, 2011, at 12:00 PM, <a href="mailto:postgis-users-request@postgis.refractions.net">postgis-users-request@postgis.refractions.net</a> wrote:</div></div><meta charset="utf-8"><span class="Apple-style-span" style="font-family: Times; "><pre style="font-family: courier; font-size: 10pt; ">Hi Peter,
Here is a link to OSGeo workshop that should be a helpful premier on the
issue in general and provides a solution to your problem through the use
of PostGIS's geography type:
<a href="http://workshops.opengeo.org/postgis-intro/geography.html">http://workshops.opengeo.org/postgis-intro/geography.html</a>
If you are dealing with a fairly well define area, say the West Coast of
the US and Canada, then you might consider reprojecting your data out of
NAD83 (North American Datum of 1983) geographic (lon/lat) coordinates
(EPSG: 4269) into Euclidean coordinates (such as NAD83 UTM 10N), and
then you can use the standard st_area tool and the result will be in meters.
Dan
On 05/20/2011 11:57 AM, Peter Hsu wrote:
><i> I have a simple question. I've loaded up shape files from the tigerline US census bureau. Everything works fine, but I'm trying to find the area of a geometry in meters. However, I'm only able to get the area in SRID units.
</i>><i>
</i>><i> How can I convert from SRID units to meters? Is this a linear conversion? Or is it dependent on the latitude of the area in question?
</i>><i>
</i>><i> The SRID for the tigerline files is 4269
</i>><i>
</i>><i> Peter
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