The SEDRIS Data Representation Model
APPENDIX A - Classes
GM Location 3D

Class Name: GM Location 3D

Superclass - <Location 3D>

Subclasses

This DRM class is concrete and has no subclasses.

Definition

An instance of this DRM class specifies a coordinate within the Geomagnetic (GM) 3D Spatial Reference Frame (SRF).

See [I18026] for a complete definition.

Primary Page in DRM Diagram:

Secondary Pages in DRM Diagram:

This class appears on only one page of the DRM class diagram.

Example

  1. The positions of magnetic observatories are often expressed in geomagnetic coordinates.

  2. Positions of charged particles affected by the Earth's magnetic fields, as well as the magnetic fields themselves, can be expressed conveniently in geomagnetic coordinates.

FAQs

How is the dipole position determined?

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.

When the ORM represents the Earth, how is the centre of Earth defined, and what is the shape of the surface of Earth that is being assumed?

The references that discuss the geomagnetic 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 GM 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 GM and other SRF locations (e.g. GD).

The matrix transformation outlined above assumes that the user has already converted the geodetic (GD) { latitude, longitude, altitude} to a geocentric (GC) vector. This conversion is where the shape of the Earth is important. Likewise, once the GM vector is obtained, the shape of the Earth is important in the conversion from the GM vector to a GM { latitude, longitude, radius}.

Where can users obtain further information on GM?

See the Spatial Reference Model (SRM) for additional details.

Constraints

Component of (two-way)(inherited)

Inherited Field Elements

This class has no inherited field elements.

Field Elements

SRM_GM_Coordinate_3D coordinate;
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Last updated: May 15, 2003 Copyright © 2003 SEDRIS™