[postgis] SRID for LAT/LONG

Frank Warmerdam warmerdam at pobox.com
Fri Sep 28 14:30:39 PDT 2001

Roderick A. Anderson wrote:

> A few questions.
> 1.  Is there a generally accepted or defned AUTH_SRID for LAT/LONGs?


If you use EPSG as your authority, there are a lengthy list of Geographic
Coordinate systems.  Essentially these are lat/long with different datums.
A few common ones follow.  I can provide the WKT if you want, or you can
look it up in the ct_epsg.txt file yourself.

4326: WGS84
4267: NAD27
4269: NAD83

> 2.  Does or will PostGIS support LAT/LONG and Elevations as a coordinate
>     system?

Do you mean, will PostGIS allow you to use a compound coordinate system
descripting the horizontal (lat/long) and vertical (elevation) axeses?
There is a way to do this in WKT, but it isn't widely used yet.  Since
PostGIS doesn't do anything special with the 3rd dimension I would encourage
you to just use the 2d coordinate system descriptions, and maintain the
interpretation of the elevation yourself.

If you mean, will PostGIS let you use points with x=long, y=lat and
z=elevation, yes, it certainly will.

> 3.  Does or will GiST indexes support LAT/LONGs when determining the
>     bounding box for the GIS object?

I have used lat/long layers and had no problem with indexing.


Best regards,

I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | Geospatial Programmer for Rent

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