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

[Burgholzer,Robert]

Paul,
Agreed that there is very little way to prevent people from making
dangerous inferences about in appropriate topics, so consider the
following:

Maybe part of the advanced options, or a corollary of such a function
could be a report of just how far the envelope has been pushed, i.e., a
percentage report describing the portion of the object that resides
totally within the bounds of the UTM zone, 0.0 - 1.0, and perhaps a
report of the comparison of area of shape to area of UTM zone, also 0.0
- 1.0.  

Another approach, and now I am totally spitballing since I know little
about geodetics, is some type of rotating UTM zone.  i.e, can one simply
define new center points for a "virtual" UTM zone, and adjust any other
related parameters that describe the spheroid and such?


Robert W. Burgholzer
Surface Water Modeler
Office of Water Supply and Planning
Virginia Department of Environmental Quality
rwburgholzer at deq.virginia.gov
804-698-4405
Open Source Modeling Tools:
http://sourceforge.net/projects/npsource/

-----Original Message-----
From: postgis-users-bounces at postgis.refractions.net
[mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of Paul
Ramsey
Sent: Thursday, May 15, 2008 10:57 AM
To: PostGIS Users Discussion
Subject: Re: [postgis-users] Newbie questions: SRIDs, function return
values

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

On Thu, May 15, 2008 at 7:45 AM, Markus Schaber <schabi at logix-tt.com>
wrote:
> Hi, Paul,
>
> "Paul Ramsey" <pramsey at cleverelephant.ca> wrote:
>
>> There's no universal answer to this, but I have long thought that a
>> simple answer suitable for may people would be a ST_UTM(geom) wrapper
>> on transform that picks the appropriate UTM zone for a given
geometry.
>> It would work perfectly well for any collection of small objects. It
>> would fall apart for larger things like states and countries that are
>> of similar size to a UTM zone.
>
> The function could simply use the centroid of the bounding box, that
> shoul be fast enough.
>
>
> Regards,
> Markus
>
> --
> Markus Schaber | Logical Tracking&Tracing International AG
> Dipl. Inf.     | Software Development GIS
>
> Fight against software patents in Europe! www.ffii.org
> www.nosoftwarepatents.org
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