Aaron,
If you want to learn more about the details of projections, I recommend the
publication:
Snyder, John P., Map Projection - A Working Manual: U.S. Geological Survey
Professional Paper 1395, 383 p.
This is a well written exposition of most of the common projections. I
doubt that it will answer all of your questions but it is a very good place
to start.
*******************************************************************************
Joseph (Joe) S. Duval
Geophysicist, Eastern Mineral Resources Team
12201 Sunrise Valley Dr. MS 954
Reston, VA 20192
Phone: 703-648-6106 FAX: 703-648-6383
"Aaron Balasch"
<[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]>
Sent by: cc:
[EMAIL PROTECTED] Subject: [geonet]: Projections
eosoft.com
11/10/00 01:23 PM
Please respond to
geonet
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]
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