Specifications

VP ONCORE COMMAND REFERENCE
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8 CHANNEL POSITION/STATUS/DATA
EXTENSION MESSAGE (@@Ek)
This message contains information that can be considered an extension
of the data output in the @@Ea 8 Channel Position/Status/Data
message. Some users may have applications requiring use of this data
at the same rate as the @@Ea message while other users may only
need portions of this data at a much slower rate (e.g., magnetic
variation).
Magnetic variation can be used to correct the true north heading (see
Position/Status/Data Message) to magnetic north. The correction is
computed using an algorithm developed by the U.S. Naval
Oceanographic Office. It is based on the WMM-95 (World Magnetic
Model 1995) magnetic field model which was generated from actual field
measurements and was valid until January 1, 2000. Another table will be
available from the U.S. Defense Mapping Agency (DMA) at that time.
The algorithm primarily characterizes that portion of the Earth's magnetic
field which is generated by the Earth's conducting fluid outer core.
Portions of the geomagnetic field generated by the Earth's crust, mantle,
ionosphere, and magnetosphere are for the most part not represented in
these models. Consequently, a magnetic sensor such as a compass or
magnetometer may observe spatial and temporal magnetic anomalies
when referenced to the appropriate World Magnetic Model. In particular,
certain local, regional, and temporal magnetic declination anomalies can
exceed 10 degrees. Anomalies of this magnitude are not common, but
they do exist. Declination anomalies on the order of 2 or 3 degrees are
not uncommon, but are of small spatial extent and relatively isolated.
From a global perspective, the root-mean-square (RMS) error at sea
level of the World Magnetic Model are estimated to be less than 1.0
degrees over the entire 5-year life of the model.
134 Synergy Systems, LLC 05OCT01