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Re: [udig-devel] Re: CRS - "Bursa wolf parameters required."
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Dean,
What you describe is essentially the "use the EPSG database" solution
which has been bandied about geotools for over a year now. It is more of
an implementation effort thing: noone has gone and done it yet. The
expedient solutions have been "good enough".
That said, the EPSG database alone will not actually solve the problem
that gave rise to this thread. Jesse was instantiating a projection from
a .prj file associated with a shape file, and that .prj file did not
include datum transformation information. In order to fix the problem,
at CRS instantiation time the datum name needs to be matched against a
"known" datum somehow, so the transformation information can be added
post facto.
Paul
Dean C. Mikkelsen wrote:
Just an idea...I've been following this Bursa-wolf thread since the
start.
The EPSG has implemented the code into a SQL for MySQL. With some
modifications to the SQL, could it not be implemented into PostGIS and
become part of the data model. Hence the codes could be looked up in the
DB, rather than maintaining an external file.
I'm based in North Vancouver, a geodesist by training, and was involved
in the APSG and EPSG over my past 11 years. I was in oil and gas
exploration data management and GIS.
I am relatively new to uDig and MapServer, but learning the ropes pretty
quickly.
I may be totally off the boat here, but then again, it's just an idea.
Kind regards,
Dean
Dean C. Mikkelsen, B.Sc., P.Eng.
Terra ETL Ltd.
Phone: 604-929-8630
E-mail: dcmikkelsen@xxxxxxx
-----Original Message-----
From: udig-devel-bounces@xxxxxxxxxxxxxxxxxxxxx
[mailto:udig-devel-bounces@xxxxxxxxxxxxxxxxxxxxx] On Behalf Of Paul
Ramsey
Sent: April 20, 2005 3:37 PM
To: User-friendly Desktop Internet GIS
Subject: Re: [udig-devel] Re: CRS - "Bursa wolf parameters required."
Direct GeoTools access to the EPSG database is a "great idea" that noone
has actually implemented. It was once implemented, but is not working
now. The only "epsg" data we have now is a WKT properties files I hacked
up many moons ago, precisely because the EPSG database was not working /
ready.
Yes, if we had an ESPG database, the DatumAliases could also reference
an EPSG datum ID, which in turn would allow us to look up transforms
between those actual datums, which would be very nice. But we would
still need to do the DatumAliases trick.
P
Matthias Basler wrote:
Paul Ramsey wrote
One thing we can do (prepare for the pain) is to add yet more
information to our DatumAliases -- for each DatumAlias, add the BW
transform parameters to WGS84. That way, if we come across a
particular
datum name, but lack TOWGS[] information, we can fill it in ourselves.
Otherwise it'll be death and destruction quite frequently: most apps
generating WKT do *not* generate the TOWGS[] portions of the WKT.
Maybe this is a very stupid question: Doesn't support GeoTools the use
of the
EPSG database for getting the transformation parameters? AFAIK most
CRS are
exactly defined in the EPSG database (including Bursa wolf parameters
and other
means of reprojection), so all missing information can be retrieved
from it,
cannot it?
Since I'm interested in the reprojection functionality myself, maybe
someone can
shortly outline to me how this currently handled in uDig/GeoTools2.1.
Matthias Basler
c9bama@xxxxxxxxxxx
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http://udig.refractions.net
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_______________________________________________
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http://udig.refractions.net
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