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List:       postgis-users
Subject:    Re: [postgis] SRID for LAT/LONG
From:       "Roderick A. Anderson" <raanders () tincan ! org>
Date:       2001-09-28 22:33:22
Message-ID: Pine.LNX.4.10.10109281518510.12506-100000 () tincan ! org
[Download RAW message or body]

I'm going to severely trim so this doesn't keep getting longer and
longer.

On Fri, 28 Sep 2001, Dave Blasby wrote:

> The problem with using LAT/LONG has to do with the math involved in
> making "simple" calculations is really really really difficult.

Yeah I remember this stuff from surveying courses.  Ouch I feel my head
aching again!

> 
> 	PostGIS assumes your locations are in rectangular coordinates (X,Y). 
> You can run into troubles if you put in lat/long co-ordinates.

OK so I'll need to convert to 'some' other coordinate system.  I've been
collection free data and the last bunch came in LAT/LONG - therefore my
questions. 

> Also, the bounding box maybe incorrectly calculated.  For example,
> the bounding box for LINESTRING(25 25, 40 25) will be BOX3D(25 25 0,
> 40 25 0)

So the bounding boxes are 3D even if there is no z coord ie. assuming 0
elevation.

> On the other hand, postgis has no problem storing lat/long/height
> information.  There's even a few functions ( length_spheroid(), 
> length_spheroid3d() ) for doing calculations on an ellipsoid.  

This something new.  I don't see it in the documentation for 0.6.

> Note that OpenGIS [incorrectly] calls ellipsoides "spheroids".

Everyone knows circles are just degenerate ellipses!  Does this mean
OpenGIS is degenerate?  ;-)


Thanks for the time and explanations,
Rod
-- 
                      Let Accuracy Triumph Over Victory

                                                       Zetetic Institute
                                                        "David's Sling"
                                                         Marc Stiegler


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