2 messages.------------Johnnie
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: Duane F Marble <[log in to unmask]>
: Re: Looking for technical references on projections
: Fri, 18 Aug 1995 17:44:01 -0400 (EDT)
Those interested in references on map projections are refered to John
Snyder's bibliography on the subject. There are about 2800 references
in his listing and it is available for downloading or search by pointing
your Web brouser toward:
http://thoth.sbs.ohio-state.edu
and looking under "Departmental Resources."
In addition, the book
Bugayevskiy, Lev M. and John P. Snyder, 1995. MAP PROJECTIONS: A REFERENCE
MANUAL. London: Taylor & Francis. ISBN 07484-0304-3 (paper) is now
available.
--
Duane F. Marble E-mail: [log in to unmask]
Dept. of Geography Home Page: http://thoth.sbs.ohio-state.edu
The Ohio State University Telephone: (614) 292-2250
Columbus, OH 43210 Fax: (614) 292-6213
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: Fri, 18 Aug 95 21:18:20 EDT
: [log in to unmask] (Gerald I. Evenden)
: Re: Looking for technical references on projections
>Date: Fri, 18 Aug 1995 16:31:55 EDT
>From: Steve Mykytyn <[log in to unmask]>
>Subject: Looking for technical references on projections
>
>----------------------------Original message----------------------------
>We've got most of Snyder's USGS publications, have implemented many of his
>methods, and have source from most of the generally available projection
>programs on the Internet.
>
>Looking specifically for references on:
>
>1. Projection interruption. Is this as simple as we think?
Depends upon your point of view. Fully implemented Goode projection
has segments giving repeated coverage. Thus one's clipping procedures
must be able to multiply plot a feature in different segments.
>2. Drawing lines/polygons across projection boundaries. Have seen GMT's
>methods, wondering if there's a reference and any experience with
>efficiency of implementation ( i.e., do it when you apply projection, do it
>at draw time, etc.)
Without giving it too much thought, I have used linked clip regions---
success or failure in one leads to another. Always used at least two:
geographic space clip (simple plate carree treatment), projection
operation followed by cartesian space clip. One can set up any number
of linked operations. What can get messy is if the geographic space
clip window does not follow latitude or longitude rhumblines. But
something like Goode can be easily put into such a system.
I assume that your reference "across projection boundaries" means across
segmented projection regions.
>3. Controlling field of view for Tilted Vertical Perspective projection.
>In Snyder's book the pictures had to have more parameters controlling the
>drawing than the projection parameters listed. Intuitive/reasonable ways
>for controlling how much of the projected view is displayed?
In this case, you will have clipping by the terminator (a complex curve)
in geographic space, but cartesian space will also need clipping.
>_______________________________
>Steve Mykytyn -- [log in to unmask] -- voice 415.491.1770 -- fax 415.491.1251 --
IMHO, segmented projections are a royal pain in the posterior and I
seriously question their value. I feel that many viewers find the
segmentation a detraction and it does little to enhance the visualization
of the map's theme. Despite some increase in distortion, I would
suggest using a pseudo cylindrical for global presentations. This
atitude was a factor that induced the Natl. Geog. Soc. to use Van Der
Grinten and later Robinson for most global maps.
Gerald (Jerry) I. Evenden Internet: [log in to unmask]
voice: (508)563-6766 Postal: P.O. Box 1027
fax: (508)457-2310 N.Falmouth, MA 02556-1027
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