Aaron,
Ian MacLeod's answer pretty much covers the reasons why projections,
datums and spheroids are such a wormcan. They really are. Ian was
working closely with the SEG's G&M standards sub-committee to sort this
stuff out, while developing a satndard for GXF which incorporated the
projection system information.
The definitive reference is the website and database maintained for the
European Petroleum Survey Group, which is a little group of chief
surveyors of major oil companies. They provide an Access database with
all this stuff in it and it's the only near-complete and up-to-date
resource, barring what's implemented (based on this) in mapping software
(like Geosoft).
Look at:
http://www.petroconsultants.com/products/geodetic.html
Alan Reid
------------------
> Aaron Balasch wrote:
>
> Something I've been wondering about for a long time but never took the
> time to figure out the intricacies of it. I just learned how to do
> what I needed and never minded the rest. I finally took the better
> part of this morning reading the book about projections. I don't have
> a solution, but it seems to me that there must be a way to cut down
> the amount of information(i.e. about 50 different ellipsoids, about 50
> different local transformations, etc). For instance, is Bessel 1841
> used anywhere, is Airy 1830 neccessary - doesn't Airy modified 1849
> replace it, etc.
>
> After reading through the book and help files, I still have a couple
> questions. When I but a topographic map of Canada(of say B.C.) it says
> it uses the NAD27 ellipsoid. It doeasn't say what local transformation
> it uses? One might assume that it's [NAD27]Canada(AB/BC) but
> assumptions can be dangerous. I also went through all the mapproj.csv,
> ldatum.csv, etc. files. I found where the ldatum.csv file calls the
> datum for say [Nad 27]Canada(Ont.&Man.) but couldn't find the call to
> the appropriate datum for [Nad27]Canada(BC./AB). Did I just not look
> hard enough?
>
>
>
> Aaron Balasch
> Sky Hunter Technologies Inc.
> Suite 101, 1725 10th Avenue S.W.
> Calgary, Alberta T3C 0K1
> Phone: (403)228-2175
> Fax: (403)244-7955
> email: [EMAIL PROTECTED]
--
Alan B Reid PhD
Reid Geophysics
49 Carr Bridge Drive
Leeds LS16 7LB
UK
Phone: +(44)-113-261-0252
Fax: +(44)-113-293-0062
e-mail: mailto:[EMAIL PROTECTED]
website: http://www.reid-geophys.co.uk
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