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The SEDRIS Data Representation Model
APPENDIX A - Classes CM 3D Location |
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An instance of this DRM class specifies a coordinate within the Celestiomagnetic 3D SRF.
See [ISO/IEC 18026] for a complete definition.
The positions of magnetic observatories are often expressed in celestiomagnetic coordinates.
Positions of charged particles affected by the Earth's magnetic fields, as well as the magnetic fields themselves, can be expressed conveniently in celestiomagnetic coordinates.
The International Association of Geomagnetism and Aeronomy (IAGA) updates the dipole position every 5 years, and 1995 is the epoch for the current location. The U.S. representative to the IAGA working group is John Quinn at the USGS in Golden, CO: 303-273-8475, [email protected] The U.S. Air Force's AFRL / VSB maintains the value of the standard radius of the Earth; this value is currently set at 6378145.0 metres.
The references that discuss the celestiomagnetic coordinate system (e.g., Handbook of Geophysics and the Space Environment, Airforce Geophysics Laboratory) do not define the centre of the Earth and the shape of the Earth, because the applications for ionospheric and near-Earth space analysis that use this SRF do not require a formal or precise standard defining the centre or the shape of the Earth. If a model were to apply a more precise measure, the output of the model would be essentially unchanged because the inaccuracy inherent in the model is large compared to the differences between the assumption of a spherical earth and another, more accurate ellipsoid. The SRM defines the CM SRF consistent with the World Geodetic System 1984 (WGS-84) ORM definition of the Earth's centre and surface ellipsoidal shape. This allows unambiguous interconversion of CM and other SRF locations (e.g. CD).
The matrix transformation outlined above assumes that the user has already converted the celestiodetic (CD) { latitude, longitude, altitude} to a geocentric (GC) vector. This conversion is where the shape of the Earth is important. Likewise, once the CM vector is obtained, the shape of the Earth is important in the conversion from the CM vector to a CM { latitude, longitude, radius}.
See the SRM for additional details.
| SRM_Spherical_3D_Coordinate | coordinate; | (notes) |
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The coordinate field specifies the coordinate values.
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