[postgis-users] Re: Error in SPATIAL_REF_SYS table

[Frank Warmerdam]

On 11/9/05, Patrick <pvanlaake at users.sourceforge.net> wrote:
> The second option is to analyze the EPSG area_of_use information that is
> included in several EPSG tables. IIRC all datum transforms have this
> information attached to it. Based on the extent of the data to be
> transformed you can then choose the appropriate set of parameters. For
> PROJ.4 this would require a new file that has all this information in there,
> or a live link to the EPSG database in PostgreSQL. The PostGIS
> spatial_ref_sys is useless here because it uses your (?) logic (sorry about
> that) and thus has no alternatives to offer.

Patrick,

My understanding is that EPSG has recently incorporated
actual lat/long bounds for the areas of use, whereas they
used to just be texual desriptions of the area of use.  So
this process should be much more practical now than it was
in the past.

> > Some datums also provide shifts to some other intermediate
> > datum which then has shifts to WGS84.  My logic is to weak
> > to follow these.
> >
> Isn't that true for all of us. The EPSG database is one of the more
> convoluted databases I have come across in many years, but what a resource
> it is!

Well, EPSG has tried to capture information about how
coordinate systems are used in the real world, including
alot that are essentially historical now.  And that has added
greatly to it's complexity.   It is a great resource, but still
a tall mountain to climb.

Best regards,
--
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
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