RES: [postgis-users] User Friendly vs Explicit

[Mike Leahy]

I'm just wondering if there is a listing anywhere that makes it
relatively easy to look-up SRIDs.  In the spatial_ref_sys table there
are over 2600 records, and after a bit of searching around, I've found
that if somebody wanted to find the the appropriate SRID for a
particular projection in PostGIS the only way to find it (that I can
see) is to search through this table in PostGIS/PostgreSQL.  Maybe it
would be useful to make a more readable document, or maybe a web-page
somewhere that allows users to browse the spatial_ref_sys table in a
more user-friendly way, or perhaps such a thing already exists and I
just don't know what to look for.

Mike

Gustavo Henrique Sberze Ribas wrote:

>  Some links about projections and the Earth:
>
>
> The Earth:
> http://www.gfz-potsdam.de/news/foto/images/GFZ-Potsdam-PR-20030122-Geoid-Undulation-1250x1250.jpg
>
> How to map the Earth:
> http://kartoweb.itc.nl/geometrics/Reference%20surfaces/body.htm 
> http://exchange.manifold.net/manifold/manuals/5_userman/mfd50The_Earth_as_an_Ellipsoid.htm
> http://solid_earth.ou.edu/notes/geoid/earths_geoid.htm
>
> Map Projections:
> http://www.fes.uwaterloo.ca/crs/geog165/mapproj.htm
>
> Check the Data Standards section:
> http://maic.jmu.edu/sic/topics.htm
>
>
>
>--
>Gustavo 
>
>
>-----Mensagem original-----
>De: postgis-users-bounces at postgis.refractions.net [mailto:postgis-users-bounces at postgis.refractions.net]Em nome de Mark Fenbers
>Enviada em: sábado, 14 de maio de 2005 20:17
>Para: PostGIS Users Discussion
>Assunto: Re: [postgis-users] User Friendly vs Explicit
>
>
>Mark Fenbers wrote: 
>Norman Vine wrote: 
>This is commonly referred to as the Vornoi Diagram
>http://www.cs.cornell.edu/Info/People/chew/Delaunay.html
>
>program that can compute this for you
>http://www-2.cs.cmu.edu/~quake/triangle.html
>
>  
>Wow!  I never knew this had a name!  Your info was interesting and helpful, but I want to calculate Voronoi Diagrams using PostGIS so that all I have to pass around is some SQL to each site having different radars to work with...  I have yet to find documentation that makes it clear to me why SRIDs (other than -1) are useful, and how to reproject lat/lons into a planar projection.  I see that the distance() function also needs reprojected data to be useful...
>
>
>OK, well, reading through more documentation and online stuff, I learned of a spatial_ref_sys.sql file that wasn't run during installation.  So now I have the spatial_ref_sys table populated and now understand that SRID relates to different map projections.  But this brings up even more questions, like "How in the world (figuratively) will I be able to pick an SRID that's right for the work I am doing?"  And is the use of SetSRID() what actually reprojects my data?
>
>Mark
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