[postgis] SRID for LAT/LONG

Roderick A. Anderson raanders at tincan.org
Fri Sep 28 15:33:22 PDT 2001

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

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

> 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

> 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,
                      Let Accuracy Triumph Over Victory

                                                       Zetetic Institute
                                                        "David's Sling"
                                                         Marc Stiegler

------------------------ Yahoo! Groups Sponsor ---------------------~-->
Get your FREE VeriSign guide to security solutions for your web site: encrypting transactions, securing intranets, and more!

To unsubscribe from this group, send an email to:
postgis-unsubscribe at yahoogroups.com


Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/ 

More information about the postgis-users mailing list