GeoMagneticInfo Application for the Palm OS
The GeoMagneticInfo is an application for the Palm OS to compute the magnetic declination,
inclination, and magnitude for any location on Earth.
Its main use is to give the current magnetic declination to correct a magnetic compass.
This application is most useful for those hiking and traveling without topographic maps in
unfamiliar territory. A magnetic compass can be off by many 10's of degrees in parts of the
This application is also useful for correcting the magnetic declination of old topographic maps
and navigation charts. The change in declination per year is surprisingly high.
About GeoMagneticInfo Version 1.3
Version 1.3 provides the ability to import location data from the GeoDB database (available in version
1.2) and allows multiple Geomagnetic Models to be installed and one to be choosen as the active model.
Otherwise it has no new functionality over V1.1 and V1.2. However, if you have any of
the previous versions installed in your Palm you should delete GeoMagInfo and GeoMagLLib, then install
the files in the V1.3 zip archive.
The program structure is different than V1.0 in that the computation is broken into two parts: the
main program (geomag13.prc), and a geomagnetic library (gmiLLib12.prc). This allows other applications to
share the library. It has the additional benefit that the total memory used in the Palm by
GeomagneticInfo is actually a little smaller.
The geomagnetic library (gmiLLib12.prc) is shared by RiseSet Versions 2.0 and 2.1.
This archive file includes:
GeoMagnaticInfo requires four files to be installed: the first three in the list above, and one or
more of the model databases.
- The Palm executable application.
- The required geomagnetic function library.
- The required mathematics library -- V1.1.
- wmm-2000.pdb, igrf-2000.pdb, us-2000.pdb, ak-2000.pdb, hi-2000.pdb
- Pre-compiled geomagnetic model databases.
- wmm-2000.cof, igrf-2000.cof, us-2000.cof, ak-2000.cof, hi-2000.cof
- All geomagnetic models available as of this release date.
- A DOS Window program to compile geomagnetic models into GeoMagneticInfo databases.
- This file.
- gmimain.gif, gmimenu.gif
- Image for geomaginfo.html.
Note: gmimodel.exe, geomaginfo.html, gmimain.gif and
gmimenu.gif are not installed in your Palm.
- Delete GeoMagInfo and GeoMagLLib if you have one of the previous versions installed in
- Use your Palm installer to install:
- MathLib.prc (unless you already have MathLib.prc installed, or you wish to upgrade to V1.1), and
- one or more of the geomagnetic model databases.
wmm-2000.pdb is the most general for all location on earth.
Later see About Geomagnetic Models to decide which models are best for you.
Using the Program
At first launch you will see "Choose a Model" as the current model name.
Tap that statement and select one of the models you have installed in your Palm OS.
To do this cycle through the model names using the Next button, in the dialog screen.
When you find the one you want tap the Open button. GeoMagneticInfo is then ready.
You can change the active Geomagnetic Model whenever you wish with the Open Model menu.
To use GeoMagneticInfo simply enter the desired location's Latitude and Longitude, and tap
The input for latitude and longitude may be in any of the following formats:
- Degrees -- e.g. 44.6427
- Degrees:Minutes -- e.g. 44:38.562
- Degrees:Minutes:Seconds -- e.g. 44:38:33.72
The only allowable input characters are: digit, '.' and ':'. That is, digit, period, and colon.
Be sure to set the correct direction for the location -- West, East, North or South using the
pop-up selection list to the right. The pop-up selector lists choices are only East or West, or North or
You may enter a name for this newly entered location by tapping to the right of the
The date displayed is that of the previous use of GeoMagneticInfo. To change it tap the date and
then select the desired date in the Date dialog box.
Hopefully the program output is self explanatory. The three terms used are:
Declination is the magnetic declination at the specified
latitude, longitude and date. A magnetic compass reading can be corrected to the direction relative to
true north by adding the declination to the compass reading.
Inclination is the angle a vertical reading compass will
show at the location.
Intensity is the magnitude of the magnetic field at the
location. The units are nanoTeslas (nT).
Actions of the menu items:
About Geomagnetic Models
Supplied with this release are 5 geomagnetic models. They are supplied in both raw format (.cof)
and compiled format (.pdb). The later .pdb format is ready to install in GeoMagneticInfo.
Models wmm-2000.pdb and igrf-2000.pdb are World Magnetic Models -- i.e. have reasonable accuracy world
Models us-2000.pdb, ak-2000.pdb and hi-2000.pdb are Regional Models for the United States,
Alaska, and Hawaii respectively.
Getting Updated Geomagnetic Models
The Geomagnetic Models are updated every 5 years, as explained in the next section. All available
models at the date of this release are included in both the raw format, as supplied Geological
Survey, and the Palm database format (.pdb) as need by GeoMagneticInfo. The next major release will
be in 2005. However, other models may become available. The URL to look for new or updated models is:
http://geomag.usgs.gov. Also you can contact John M. Quinn, as
If you wish to use a new or updated model, you must compile it with the supplied computer program:
gmimodel.exe. It runs in a MSDOS window of Windows 95/98 (and the Command window of newer Windows). The
compiled output must then be installed with your Palm installer.
This assumes that gmimodel.exe and the raw geomagnetic model data files *.cof model(s) are in the
same directory which we call "mygeomag".
You should keep all of the GeoMagneticInfo models since you can re-install any one of them at any
time. This is particularly true if you are using regional models.
- Open a MSDOS (or Command) window.
- Change directory to mygeomag, using the cd command. (cd
- Key in gmimodel and press Enter.
- A DOS window will pop up. It will show all of the .cof models available in directory mygeomag.
Type the name of the model you wish to use and press the Enter key.
- The compiled model for GeoMagneticInfo will be found in mygeomag with the name of the model
you selected and with the extension of .pdb. Install it into your Palm with your installer. It
will replace the previous model used by GeoMagneticInfo.
About the Geomagnetic Field and Geomagnetic Models
That portion of the geomagnetic field generated in the Earth's core is
referred to as the Main magnetic field simply because it is the largest contributor to the
total geomagnetic field. It ranges in magnitude between 20,000 nanoTeslas (nT) at the
geomagnetic equator to about 65,000 nT at the magnetic poles.
Magnetic models, charts and maps which are used in a wide range of
commercial and military navigation and attitude/heading reference systems must be
Typically, the Geological Survey predicts the magnetic field strength and direction,
and the rates of change of these quantities, both on a regional basis and on a global
basis, 5 years in advance, in accordance with international scientific recommendations set
in the 1950's by the International Association of Geomagnetism and Aeronomy (IAGA). A
continuous flow of new data involving millions of measurements, which must be reduced,
extensively analyzed, corrected, culled, edited and prepared for modeling, is essential in
order to make these predictions. The Geological Survey produces Regional Magnetic Models
(RMM's) of the Main magnetic field and its corresponding Secular Variation for the 48
conterminous states, Hawaii, and Alaska, known collectively as the U. S. National models.
The Geological Survey also generates World Magnetic Models (WMM's). These models in turn
are used to generate regional, national, and global charts and maps for several Main and
Secular Variation vector-magnetic-field components of the Earth.
Digital information generated from the U. S. National Models, and the USGS
and IGRF World Magnetic Models are available through the USGS/NGIC on-line and
off-line information services.
Send e-mail inquiries to John M. Quinn;
or you may write, FAX, or phone him at:
National Geomagnetic Information Center
U.S. Geological Survey Box 25046 MS 968
Denver Federal Center Denver, Colorado 80225-0046 USA
TEL: +1 303 273-8475
FAX: +1 303-273-8450
The 2000 geomagnetic models supplied with GeoMagneticInfo have been obtained from John M. Quinn.
About the GeoMagneticInfo Algorithm
The algorithm used by the GeoMagenticInfo computation is derived from a public domain FORTRAN
program by John M. Quinn and associates. The entire package of PC geomagnetic programs and models
is available for download at:
As in the public domain FORTRAN, the computation uses up to a 12 degree polynomial. It is possible
that the underlying data supplied by the USGS and IGRF have coefficients which support higher degree
polynomials. The supplied *.cof data for GeoMagenticInfo is limited to 12 degrees.
GeoMagneticInfo was created by
David W. Bray, Potsdam, NY;
Copyright © 1999-2005 David W. Bray, All Rights Reserved.
The Bray Palm OS Page can be found at:
GeoMagneticInfo is freeware no registration is required. We hope you enjoy using it.
This archive may be freely redistributed, provided it is made available
only in its complete, unmodified form with no additional files and for
noncommercial purposes only. Any other use must have prior written
David W. Bray
Unauthorized commercial use includes, but is not limited to:
- GeoMagneticInfo itself as a product for sale.
- Accompanying a product for sale.
- Accompanying a magazine, book or other publication for sale.
- Distribution with 'Media', 'Copying' or other incidental costs.
- Available for download with access or download fees.
This program is provided without warranty and the user accepts full responsibility for
any damages, consequential or otherwise, resulting from its use.
*Many thanks to Rick Huebner, the author of MathLib, for his excellent routines and
making them freely available.
*Changes in Version 1.3 from that of Version 1.0
A Bld: (build) has been added to the version number in the 'About' box.
To be sure that your version is up-to-date check the Bld: number in the description of
GeoMagenticInfo at: http://davidbray.org/palm/
- The program structure was changed to use a shared geomagnetic library (gmillib.prc). (V1.1)
- The ability to name the location. (V1.2 Bld:249)
- The ability to import GeoDB locations was added. (V1.2 Bld:249)
- Bug in Palm TxtCharIsDigit() - replaced by local routine. (V1.2 Bld:303)
- The ability to choose the active Geomagnetic Model amoung those installed (V1.3 Bld:344).
The original release of GeoMagenticInfo V1.3 is Bld:344.
The current Bld: is 344.