GeoMagnetic field vector

Module XML file: geo_mag.xml

Calculation of the normalized geomagnetic field vector at startup as soon as a valid location is aquired. The result is published via the GEO_MAG ABI message. The AHRS algorithms need to know the magnetic field vector at the current position in order to accurately calculate the heading.

Method uses is based on the the ngdc noaa DODWMM model and data (http://www.ngdc.noaa.gov/geomag/WMM/DoDWMM.shtml). The WMM is based on earth magnetic field measuring at an high number of sites on the whole globe and on its mathematical representation through a series of characteristic values listed in a file (WMM.COF) which has a five-year validity. The autopilot used data derived from this file to make the complex calculation of declination. Every 5 years (2015, 2020) an updated geomagnetic model is released and datatables in the code must be updated accordingly for more accurate flight.

Example for airframe file

<modules>
  <load name="geo_mag.xml"/>
</modules>

Module functions

Init Functions

These initialization functions are called once on startup.

• geo_mag_init()

Event Functions

These event functions are called in each cycle of the module event loop.

• geo_mag_event()

Periodic Functions

These functions are called periodically at the specified frequency from the module periodic loop.

• geo_mag_periodic()
  • Frequency in Hz: 1
  • Autorun: LOCK
    Periodic function automatically starts after init and can't be stopped.

Files

Header Files

The following headers are automatically included in modules.h

• geo_mag.h

Source Files

• modules/geo_mag/geo_mag.c
• math/pprz_geodetic_wmm2015.c

Raw geo_mag.xml file:

<!DOCTYPE module SYSTEM "module.dtd">

<module name="geo_mag" dir="geo_mag">
  <doc>
    <description>
      GeoMagnetic field vector.
      Calculation of the normalized geomagnetic field vector at startup as soon as a valid location is aquired.
      The result is published via the GEO_MAG ABI message.
      The AHRS algorithms need to know the magnetic field vector at the current position in order to accurately calculate the heading.

      Method uses is based on the the ngdc noaa DODWMM model and data (http://www.ngdc.noaa.gov/geomag/WMM/DoDWMM.shtml).
      The WMM is based on earth magnetic field measuring at an high number of sites on the whole globe and on its mathematical representation through a series of characteristic values listed in a file (WMM.COF) which has a five-year validity.
      The autopilot used data derived from this file to make the complex calculation of declination.
      Every 5 years (2015, 2020) an updated geomagnetic model is released and datatables in the code must be updated accordingly for more accurate flight.
    </description>
  </doc>
  <settings>
    <dl_settings>
      <dl_settings name="geo_mag">
        <dl_setting min="0" max="1" step="1" values="OFF|CALC" var="geo_mag.calc_once" module="geo_mag/geo_mag" shortname="calcNow"/>
      </dl_settings>
    </dl_settings>
  </settings>
  <header>
    <file name="geo_mag.h"/>
  </header>
  <init fun="geo_mag_init()"/>
  <periodic fun="geo_mag_periodic()" freq="1"/>
  <event fun="geo_mag_event()"/>
  <makefile target="ap|nps">
    <file name="geo_mag.c"/>
    <file name="pprz_geodetic_wmm2015.c" dir="math"/>
  </makefile>
  <makefile target="nps">
    <define name="NPS_CALC_GEO_MAG"/>
  </makefile>
</module>