About The magnetosphere package currently contains two modules: igrf and cxform.
Module igrf provides several useful methods based on IGRF v.11. The wrapper has been written by David Parunakian, Skobeltsyn Institute of Nuclear Physics of the Moscow State University. Feel free to contact me with improvement suggestions, questions etc at either rumith@srd.sinp.msu.ru or dp@xientific.info. The model itself is the result of hard work of many people from different institutions, such as IAGA and NASA. The source code and coefficient files used can be found at ftp://nssdcftp.gsfc.nasa.gov/models/geomagnetic/igrf/fortran_code/ More information on IGRF can be found here: http://www.ngdc.noaa.gov/IAGA/vmod/igrf.html
Module cxform provides access to one function - transform(), which can be used for transforming cartesian coordinates from one coordinate system to another. Complete documentation on cxform, as well as the list of coordinate systems supported, can be found at CXFORM official website http://nssdcftp.gsfc.nasa.gov/selected_software/coordinate_transform/
Installation python setup.py install
IGRF coefficient files will be installed to /usr/local/lib/igrf.
Usage To use igrf in your software after you have installed it, include the following line in your code:
import magnetosphere.igrf
After that, you can use the following functions:
igrf.dimo(year): Find the geomagnetic dipole moment in Gauss (normalized to the Earth's radius) at the specified time (decimal year)
igrf.lb(lat, lon, alt, year): Find the L-shell and geomagnetic field intensity (l, b tuple) at the specified latitude, longitude, altitude and decimal year
igrf.b(lat, lon, alt, year): Find the Earth's magnetic field value (Bnorth, Beast, Bdown, Babs tuple) using the spherical harmonics model
igrf.b0(lat, lon, alt, year, stps): Find the smallest magnetic field strength on a field line. Stps is step size for field line tracing
Latitude and longitude should be specified in the geographic coordinate system. Altitude should be specified in kilometers above sea level. Decimal year is a float and looks like 2003.45.
Similarly, to use cxform, include the following line in your code:
import magnetosphere.cxform
The cxform module provides access to one function - transform(), which can be used for transforming cartesian coordinates from one coordinate system to another. Complete documentation on cxform, as well as the list of coordinate systems supported, can be found at CXFORM official website http://nssdcftp.gsfc.nasa.gov/selected_software/coordinate_transform/
Legal This project is distributed under the terms of the GNU General Public License v.3. The full text of the license is available in the LICENSE file.
CXFORM: An IDL/C library to convert between spacecraft coordinate systems
Originally written by Ed Santiago (LANL), esm@pobox.com Modified & maintained by Ryan Boller (NASA/GSFC), Ryan.A.Boller@nasa.gov
The CXFORM package contains a set of routines to convert spacecraft coordinates from one system to another, i.e., GSE-->GSM. It is written in C and can be used as either a C library (.so or .dll) or an IDL function (via DLM -- Dynamically Loadable Module -- interface).
It has been tested under SunOS v5.7, Microsoft Windows 2000/XP, Mac OS X 10.3 & 10.4, and Linux 2.4.20-28.9. It has previously been tested under Solaris 2.6 and DEC OSF/1 V4.0.
It is largely based on Mike Hapgood's excellent introduction to coordinate transformations, along with Markus Fraenz' "Heliospheric Coordinate Systems" and Christopher Russell's "Geophysical Coordinate Transformations":
http://sspg1.bnsc.rl.ac.uk/Share/Coordinates/ct_home.htm
http://www.space-plasma.qmul.ac.uk/heliocoords/
http://www-ssc.igpp.ucla.edu/personnel/russell/papers/gct1.html/Note that since this follows much of Hapgood's formulae that are optimized for simplicity and efficiency, he specifies a level of precision of 0.001 degrees up to the year 2100 for each rotation angle, which has been deemed sufficient for space physics applications. The disclaimer applies that these should not be used for mission-critical flight applications due to their margin of error.
Formal testing has been completed as of 2004/12/01. The results can be found on the CXFORM web page. In general, they are within 1% of the results of SSCWeb's calculations (based on GEOPACK), and in many cases are within 0.01%.
Questions/comments/suggestions are welcome to Ryan.A.Boller@nasa.gov
See install.txt for instructions.
The function prototype is
new = CXFORM( pos, source_frame, dest_frame, time )where: pos is a vector of length 3, containing the position in source_frame coordinates. It can also be a 2-D array of size [3, M], where M is the number of points to convert
source_frame is an ASCII string naming the source
coordinate system, e.g., 'GSE', 'J2000'. See
"Coordinate Systems Implemented" below.
dest_frame is also an ASCII string, naming the destination
coordinate system.
time is "ephemeris seconds past J2000 (1 Jan 2000 12:00)".
The "date2es" function converts a standard Gregorian
time (mm,dd,yyyy) to Ephemeris Seconds past/before
J2000. See the included "date2es.pro" file for more
details.
new is the position, in dest_frame coordinates.Single-coordinate example:
IDL> es = date2es(9,30,1999,7,5,0) ; Sep. 30, 1999 07:05:00 UTC
IDL> pos = cxform([1,0,0], 'GSE', 'GEO', et)
IDL> help,pos
POS DOUBLE = Array[3]
IDL> print,pos
0.32034915 0.94616669 -0.046314350
IDL> Multiple-coordinate example:
IDL> imp8GEI = fltarr(3, 5)
IDL> imp8Time = lonarr(5)
IDL>
IDL> help, imp8GEI
IMP8GEI FLOAT = Array[3, 5]
IDL> help, imp8Time
IMP8TIME LONG = Array[5]
IDL>
IDL>
IDL> imp8GEI[*,0] = [-32.562, 20.085, -10.471]
IDL> imp8GEI[*,1] = [-34.415, 4.229, -6.173]
...
IDL> print, imp8GEI
-32.5620 20.0850 -10.4710
-34.4150 4.22900 -6.17300
-27.2210 -12.441 -0.34300
-9.01000 -23.380 5.39300
14.1890 -19.583 7.58900
IDL>
IDL> imp8Time = [-43200, 43200, 129600, 216000, 302400]
IDL>
IDL> imp8GEO = cxform(imp8GEI, 'GEI', 'GEO', imp8Time)
IDL>
IDL> print, imp8GEO
25.418317 28.593709 -10.471000
10.691414 32.984396 -6.1729999
-6.5404276 29.205893 -0.34299999
-20.772292 14.011294 5.3930001
-22.419840 -9.0648980 7.5890002Note that if your data is imported as [M, 3] instead of [3, M], you can transpose it using IDL's TRANSPOSE function:
IDL> correctArr = fltarr(3, M)
IDL> correctArr = TRANSPOSE(originalArr)See main.c included in this package for an example of using CXFORM in C. See install.txt for instructions on building it on your platform.
The bulk of the testing used SSCWeb's Locator Tabulator as the data source. As stated in the introduction, this service uses GEOPACK for its calculations. An included file, tester.c, was used to read in data from SSCWeb and compare it to the results of CXFORM. In addition, one data point was used from the HelioCoords transformation package documentation as a sanity check and also as a test for the heliospheric systems that are not present in SSCWeb.
See the following URL for links to the actual results: http://nssdcftp.gsfc.nasa.gov/selected_software/coordinate_transform/#Test_Results
GEI Geocentric Equatorial Inertial, also known as True Equator and True Equinox of Date, True of Date (TOD), ECI, or GCI J2000 Geocentric Equatorial Inertial for epoch J2000.0 (GEI2000), also known as Mean Equator and Mean Equinox of J2000.0 GEO Geographic, also known as Greenwich Rotating Coordinates (GRC), or Earth-fixed Greenwich (EFG) MAG Geomagnetic GSE Geocentric Solar Ecliptic GSM Geocentric Solar Magnetospheric SM Solar Magnetic RTN* Radial Tangential Normal (Earth-centered) GSEQ Geocentric Solar Equatorial HEE Heliocentric Earth Ecliptic HAE Heliocentric Aries Ecliptic HEEQ Heliocentric Earth Equatorial
This package has been designed to allow for easy additions of new coordinate systems.
All you need to do is define one transformation between the new system and any of the existing ones. Once you do that, the Perl script will generate code to convert to all others. This, of course, means that a working copy of Perl must be installed. You will need the IxHash module if it is not already installed. It can be found at http://search.cpan.org/dist/Tie-IxHash/
Here's what you do:
Edit the file cxform-manual.c and add a new function, xxxx_twixt_yyyy,
where xxxx' is any existing coordinate frame, andyyyy' is the new one.
Run "perl gen_cxform_auto.pl cxform-manual.c" from the prompt. This will create a new cxform-auto.c with support for your new coordinate system.
Build and install a new CXFORM library as described in install.txt.
Run and test it in IDL/C. That's it!
If it works, please send me your code. I will include it in the next distribution (with appropriate credit to you, of course).
2000/06/21 v0.2 Ed Santiago: Last released version from Ed. 2003/09/12 v0.3 Ryan Boller: First modified version from Ryan. Added RTN and GSEQ systems, IGRF2000 model, slightly different time manipulation, Windows support, additional documentation, and standalone C functionality. 2004/03/19 v0.4 Ryan Boller: Updated Makefile to auto-detect platform and to build under Mac OS X. HEEQ system now implemented by Kristi Keller. 2004/05/21 v0.5 Ryan Boller: Fixed small discrepancy in calculation of T0 and lambda0. Results now match those of SSCWeb's (GEOPACK- based) when the mag pole lat/lon is fixed to their values, as they haven't updated their IGRF coefficients. 2004/12/01 v0.6 Ryan Boller: Finished comprehensive testing, posted results. Updated IGRF to Revision 9. Moved cxRound, date2es, and gregorian_calendar_to_jd to cxform-manual.c so it is included in the shared library. 2006/10/19 v0.7 Ryan Boller: Updated IGRF coefficients to 10th generation. Fixed IDL DLM interface under Windows XP & IDL 6.0+. Updated installation documentation. 2009/11/25 v0.71 Ryan Boller: Updated Mac compiler flags to compile 32- and 64-bit versions on Intel- and PPC-based CPUs. Fixed memory pointer problem on 64-bit machines (now using IDL_MEMINT instead of IDL_LONG in cxform-dlm.c).
IGRF -- Version 11 ----- March 14, 2010 (updated April 30, 2010)
The International Geomagnetic Reference Field (IGRF) model is the empirical representation of the Earth's magnetic field recommended for scientific use by a special Working Group of the International Association of Geomagnetism and Aeronomy (IAGA). The IGRF model represents the main (core) field without external sources. The model employs the usual spherical harmonics expansion of the scalar potential in geocentric coordinates. The IGRF model coefficients are based on all available data sources including geomagnetic measurements from observatories, ships, aircrafts and satellites.
The IGRF model consists of sets of coefficients for a global representation of the Earth magnetic field for the years 1945, 1950, 1955, etc. There are definitive coefficient sets (DGRF####.DAT; #### = year) for which no further revisions are anticipated and IGRF####.DAT and IGRF####S.DAT for which future updates are expected. IGRF####S.DAT provides the first time derivatives of the coefficients for extrapolation into the future. The 11th generation of the IGRF model (IGRF-11) consists of definitive coefficients sets for 1900 thru 2005 (DGRF1945 thru DGRF2005) and prelimenary sets for 1900 to 1940 and for 2010 (IGRF2010) and for extrapolating from 2005 to 2010 (IGRF2010s.DAT).
In combination with the IGRF coefficient sets different subroutines have been used to determine the components of the magnetic field vector and the L-value at a given location. This sofware package uses the subroutines FELDG (magnetic field vector) and SHELLG (L shell) developed by G. Kluge at the European Space Operations Center (ESOC). His use of inverse cartesian co- ordinates simplifies the computation. The IGRF subroutines were developed by A. Zunde of the U.S. Geological Survey (USGS). FELDG and SHELLG are included togehter with other funbctions and subroutines in the file SHELLIG.FOR. The program BILCAL.FOR produces tables of the geomagnetic field strength, vector components (B-abs., B-north, B-east, B-down, declination, inclination), equatorial/minimum field strength (B0), dipole moment, and L-value in latitude, longitude (geodetic), altitude, or year (decimal). In addition to the main driver program BILCAL.FOR this distribution also includes a subroutine for computation of IGRF parameters in the file IGRF_SUB.FOR.
The IGRF homepage is at http://www.ngdc.noaa.gov/IAGA/vmod/igrf.html.