![[GPSy -- A Macintosh GPS Program]](../../images/logos/gpsylogospin.gif)
| Site Map: | [GPSy Home Page] [GPS Resource Library] |
| Site Map: | [GPSy Home Page] [GPS Resource Library] |
One note of caution is reflected in Richard Koolish's message below. Depending on the geodetic datum used, your results vary when performing coordinate system transformations. Chuck Gantz's C source listed below allows you to select which datum you wish to perform the conversion in; and even handles the Swiss Grid.
Perhaps the best source code to steal/utilize is the free MacGPS source which is on Peter Bennet's GPS Resource site. It has routines to translate to and from UTM, Lat/Lon, ITM, OSGB, UPS, etc. People have ported MacGPS to LINUX/Windows/NT and other inferior operating systems, so you can find plenty of source code to work with based on MacGPS.
If all you need to do is run the calculations between geographic (lat/long) and UTM coordinates, then use either the Lotus 1-2-3 / Excel spreadsheet below, or:
The Coordinate System Overview is an exellent overview of why various coordinate systems and datums exist.
The book that should be on every coordinate system programmer's shelf is:
Map Projections - A Working Manual John P. Snyder. USGS Professional Paper 1395.
This text as well as a list of other "required reading" in GPS and cartography can be found in the GPS Bibliography.
I welcome contributions and additions to this page via e-mail at:
. However, due to my full-time jobs
as a Macintosh GPS systems developer and sociocultural anthropologist, I am unable
to provide much assistance beyond what is already covered on this page. I would
suggest posting to the newsgroups or hiring a consultant (in which case I would
be available: my time is your time if my time is your money).
For information on transformations to other grid systems:
Hi - I was wondering if there was a computationally simple way to produce UTM readings given lat/lon. Is there something simple? Alternately, can someone recommend a good textbook on the different map systems (and conversion principles)?
Source Code
Date: Fri, 05 Jun 1998 14:32:23 -0700 From: "Chuck Gantz"
Date: Sat, 5 Oct 1996 10:44:05 +0100 From: Steve Metcalfe (
Date: Tue, 8 Oct 1996 10:45:32 -0400 From: "Donald J. Stierman" (
From: John Ceccherelli To: Karen Nakamura Subject: Lat/Long - UTM Conversion Date: Fri, 7 Nov 1997 09:24:55 -0500 Karen, I noticed your reply to a question about lat/long to UTM on the sat-nav usenet. I have a Lotus 1-2-3 worksheet which does this conversion as well as several other utilities. It's small so it can be used on PDAs like the Casio, Sharp, and HP200LX. It's freeware with no strings attached. I was wondering if you would check it out and if possible add it to your web page? I get about 10 to 20 requests a month for it and it desperately needs a home but I don't a place to put it. I've attached a UUENCODE PKZIPPED file that contains the worksheet and documentation. As you can see, it's pretty small. Thanks, John Ceccherelli [Here are the attachments] mapxv2.doc Documentation (MSWord file; 20K) mapxv2.doc.uu Documentation (MSWord; uuencoded; 27K) mapxv2.wk1 Excel sheet (12K) mapxv2.wk1.uu Excel sheet (uuencoded; 16K) mapx.zip -- Zip file (12K) mapx.zip.uu -- Zip file uuencoded (16K) [end attachments]
From: Gachoki Thomas
Date: Mon, 7 Oct 96 15:43:26 EDT From:
Date: Sat, 5 Oct 1996 10:06:13 -0700 (MST) From: [anonymous by request] To: Karen Nakamura (
Books
Date: Mon, 07 Oct 1996 11:15:25 -0500 From: [Anonymous by request] To: Karen Nakamura (
Commercial Software
Date: Mon, 07 Oct 96 09:15:54 GMT From: Jose Manuel Martinho Lourenco (
Date: Tue, 8 Oct 1996 12:14:45 +0100 From: Guillermo Ortiz (
From: Michael Wild To:
From: "James H. Maynard"
Newsgroups: sci.geo.satellite-nav
Subject: Re: Mercator Software
Date: Tue, 11 Nov 1997 02:34:57 -0800
To: Patrick Di Justo
Patrick Di Justo wrote:
> Can anyone point me to a software package (preferably freeware or
> shareware) that can take a flat rectangular image map and distort it
> into one of those mercator projection maps that seem to be made of a
> series of long vertical ovals??? I've got a digital map of the planet
> Earth that I'd like to print out and wrap around a sphere to make a
> globe, and If I'm not mistaken, only one of those ovoid mercator
> projections will work.....
I am sorry Patrick, but I find your terminology confusing.There is no such
thing as a "Mercator projection map" that is
also "made of a series of long vertical ovals." Nor is there
any map projection with the name "ovoid mercator projection."
I think you are probably talking about the UTM, Universal
Transverse Mercator, projection (really, series of projections).
A transverse Mercator projection is like the ordinary Mercator
projection, but is based on the idea of wrapping a cylinder
around the sphere or ellipsoid (used to represent the earth)
not touching the sphere at the equator, as in the normal
aspect of the Mercator projection, but along a meridian.
Just as the normal aspect Mercator projection has low
distortion of scale near the equator, so does a transverse
Mercator projection have low scale distortion near its
central meridian.
With the UTM system, the earth is divided into 60 zones
of longitude, each 6 degrees of longitude wide. Zone 1 has
its western boundary at 180 degrees W, with its central
meridian at 177 degrees W, and its eastern boundary at 174
degrees W. Likewise, zone 2 has its central meridian at
171 degrees W, zone 3 at 165 degrees W, and so on. I live
near 123 degrees W, which is the central meridian for
UTM zone 10.
Since you are interested in constructing a globe, which
is a *very* small scale map, you can model the earth as
a sphere and use the spherical, rather than the
ellipsoidal formulation of the transverse Mercator
projection.
For the formulas for the projection, you should
consult the late John P. Snyder's excellent tome,
"Map Projections - A Working Manual." For illustrations
of a wide variety of map projections, see his
"An Album of Map Projections." Both were published
by the U.S. Geological Survey. I purchased my copy
of the former from the Navtech bookstore; see their
web page at "http://www.navtechgps.com". I found my
copy of the "Atlas of Map Projections" at a local
navigational chart agent, of all places. (I only
saw it there once, the day I bought it.) I expect
both could be purchased through "http://www.amazon.com".
"Map Projections - A Working Manual" gives you the
(sometimes rather tedious) formulas for both the
spherical and ellipsoidal cases of all the major
map projections. Unless you are planning to write
your own software, just look at this book in a library.
You don't have to read all the math; the text introduction
to Mercator's projection is quite readable. If you
ever *do* want to write your own map projection
software, though, you really should have this book
in your personal library.
The "Album of Map Projections" is a most entertaining
book. It gives illustrations of a *wide* variety of
map projections and tells you how to distinguish one from
another. All the major projections are covered, as
well as many minor, but entertaining ones. There are
illustrations of conformal mappings of the world
onto a square, onto a triangle, onto an ellipse.
{I found the "Craig Retroazimuthal" project most
entertaining. Locate yourself on a Craig
Retroazimuthal projection map, and and use a
protractor to measure the angle on the map from
north to the center of the projection. This is
easy to to do since all meridians are represented
as parallel straight lines. The angle you measure
off the map is the great circle bearing from
your position to the center of the projection.
Very handy for travelling Muslims who want to
keep track of the direction to Mecca!)
But back to your question. The part of a sphere's
surface which is bounded by two meridians is called
a "gore." (It is *not* an oval or an ellipse.)
One way to manufacture a globe is to divide the
sphere into several gores (usually 24, each between
bounding meridians that are 30 degrees apart).
Then print the map for each gore using a conformal
map projection, such as a transverse Mercator
projection centered on the central meridian for
that gore. Then paste the gores together onto
your spherical surface. The more gores there are,
the easier it is to make the paper stretch
(when moist) to fit the sphere - but the more
tedious is the job of pasting!
Using the UTM projection for this would be tedious,
as there would be *sixty* gores to print and paste!
There are a variety of map projection software
packages out there, and most support the transverse
Mercator projection. I use the "Geographic Calculator"
from Blue Marble Geographics. I believe the
National Geodetic Survey has some software you can
download from their site. (It will be for an
ellipsoidal model of the earth, though, and
thus overly complicated for your purpose of
constructing a globe.)
It should be easy enough, though, to just use
the formulas from Snyder for the spherical
case of a transverse Mercator projection.
--
(To send me e-mail you must remove "nospam." from my address.)
Jim Maynard (K7KK) at Salem, Oregon, USA
e-mail:
boat: "Ruddy Duck," a Doughdish (Herreshoff 12)
motto: "Ignorance is the mother of Adventure" - Hagar the Horrible
Copyright (C) 1996-2000 by Karen Nakamura. All rights reserved.
This page was created on October 9th, 1996 and last updated on June 22, 2000.
We've had hits since we relocated on April 8th, 1997.