[postgis-users] Newbie questions: SRIDs, function return values

[Bruce Rindahl]

I have to also step in here.  PostGIS is a great tool but it can't teach 
you basic GIS concepts if people won't take the time to learn them.  To 
work in mapping and GIS you have to have at least a concept of 
coordinate systems and projections.  Otherwise anything you develop will 
still cause confusion for those who don't understand GIS but can grab 
big sets of data and put it into PostGIS as Paul states below.

The original question could be phrased as follows:

"I have a big spreadsheet table of the heights of students in my class.  
When I use the spreadsheet function =AVERAGE(...) what units is the 
average in?"
or:
"I have a big spreadsheet table of the heights of students in my class.  
The values are mixed between cm, inches, and decimal feet.  Why am I not 
getting the correct answer for AVERAGE()?"

Bruce

Paul Ramsey wrote:
> The danger of this approach is that it falls apart as people start
> pushing the limits...
>
> select blah from a, b where st_dwithin(st_utm(a.geom),st_utm(b.goem),100)
>
> It's a pandora's box... as are all things geodetic
>
> p
>
>