Date: Thu, 5 Apr 2007 10:48:36 -0400 (EDT)
Subject: My Idea for an Equatorial Map-Dial

I am working on the design for an equatorial sundial that features a polar
map projection of the Northern Hemisphere on the upper dial face and the
Southern Hemisphere on the lower dial face: the North & South Poles would be
in the center of the dial faces; the Equator around the rim of the dial
plate -- actually, slightly offset from the edge in order to make room for
numerals (hour & longitude), etc. If the observer's longitude were the 12
Noon hour line, then the Sun's shadow should (I think) show the line of
longitude along which the subsolar point falls (that is, wherever it's local
noon on Earth). I'm thinking of showing every 15deg of longitude (of course)
and only 0, 30, 60, and 90deg north & south latitude, as well as the Tropics
of Cancer and Capricorn (and Arctic- and Antarctic Circles). I plan to use
some sort of nodus to trace the line of latitude of the subsolar point
(declination of the Sun).

The biggest stumbling block preventing further development of my sundial
design is finding a software application to generate the maps. In order to
create a few test graphics, I collaborated via the Internet (long-distance)
with a friend who works with GIS -- as I recall, he used ArcInfo (ESRI's
industry standard GIS mapping app) to create the files. I could tell he was
getting tired of tweaking the output to suit my needs, so I let it go before
getting exactly what I wanted. Two obstacles stand in the way of further
development of the dial face maps using ArcInfo: 1) the software is, or was,
VERY expensive (>$10K); 2) its learning curve is VERY steep.

FYI, PDFs of the prototype maps for the upper- & lower dial faces are online
at the following URL (same directory as this file):

   http://www.wsanford.com/~wsanford/sundials/equatorial-map-dial/

I think the design has great potential for use in education, either formal
or informal, cleverly combining the content areas of geography (in the era
of standards-based testing in the U.S., a subject that is quickly
dissapearing from the public schools curriculum) and science quite nicely,
if I do say so myself.

==ref. Mac Oglesby==
See also, USGS Map Projections:
http://erg.usgs.gov/isb/pubs/MapProjections/projections.html

MO_Walter-Map-Dial.jpg -- courtesy Mac Oglesby -- illustrates the fact 
that the gnomon shadow will not reach the edge of the dial plate (on the 
date of the June Solstice) if the top of the gnomon is used as a nodus.

==ref. Fred Sawyer==
It would be interesting to see the dial, but [it's not] 'original' in the 
sense of a new development in dialing.

Back in 2002 I gave a talk on "Maps and Dialing" -- and pointed out then 
that any azimuthal map projection could be used to make a sundial at any 
latitude you choose. That's essentially what you are proposing -- two 
azimuthal projections (of one sort or another -- there are several that 
have different other useful features) centered at the poles. I made the 
observation and gave various examples, but I did not suggest that it was 
in any way a new idea.

To see an existing product similar to what you are thinking about (in a
portable format), see ...
   http://www.solarserver.de/store/produkt.produkt-1401.html
I had my example of the Icarus dial with me on display at the last NASS 
conference [2006].

You can get a shareware version of Versamap that will probably do what you 
want -- it will depend on the data points you feed into it. The software 
comes with some data sets and others are available[*].

   Versamap Mapping & Cartography Software
   http://www.versamap.com/
  *Links to free, public domain digital map data for use with Versamap
   http://www.versamap.com/webdoc03.htm

ICARUS - Sonnenuhr [Note: Web pages in German]
http://www.solarserver.de/store/produkt.kategorie-55.produkt-1401.html