[postgis] SRID for LAT/LONG

[Roderick A. Anderson]

On Fri, 28 Sep 2001, Frank Warmerdam wrote:

> Rod,
> 
> 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

Got the (a) file with this information but since it looked like it was
trying to be a semi-database with everything on one line (or two) it was
tough reading and searching it.  I remember a message about making this
a part(?) of the PostGIS distribution but the spatial_ref_sys table
isn't set up for searching (by novices).  Maybe I can create and
populate a table with all the fields in the SRTEXT broken out as
attributes (columns) for my contribution to the effort.  Would this be
useful?

> 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.

I'd prefer to use GSDM coordinates - 'cause it's the right thing to do -
but so far my web searches haven't provide too much on how to convert
to/from them with most the content centered in on Earl Burkholder's
BURKORD database/product.
   And I haven't found many references to GSDM at most GIS sites I've
checked so far.

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

Dave Blasby has a slightly different view on this I think.

I do have a strong understanding of the math involved though I lack some
of the skills for doing it so my questions are aimed at trying to find
'a way'; not to complain about a lack of features.



Rod
-- 
                      Let Accuracy Triumph Over Victory

                                                       Zetetic Institute
                                                        "David's Sling"
                                                         Marc Stiegler



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