Operation 33
Operation
The ionospheric model used by the G12 is based on the model defined in ICD-
GPS-200, Revision B. The tropospheric model is based on the Bean and Dutton
model. For more information on ICD-GPS-200, refer to ARINC Research
Corporation:
ARINC Research Corporation
2250 E. Imperial Highway, Suite 450
El Segundo, CA 90245-3509 USA
Tel: 310-524-1557
Web: http://www.arinc.com/products_services/gpshome.html
Magnetic Variation Model
The G12 uses the Joint US/UK 1995 Epoch World Magnetic Model (WMM-95).
For more information on WMM-95, refer to the USGS National Geomagnetic
Information Center:
USGS National Geomagnetic Information Center
Box 25046, Mailstop 968
Denver Federal Center
Denver, CO 80225-0046 USA
Tel: 303-273-8475
Fax: 303-273-8450
Web: http://geomag.usgs.gov
Setting Antenna Position
When in Differential Base Mode, the G12 uses an accurate antenna position
(reference position) entered by the user to calculate range corrections by
subtracting the measured range from the true range. Two commands can be used
to enter the reference position:
$PASHS,POS (position setting including latitude, longitude, altitude).
$PASHS,ALT (antenna height setting).
NMEA Outputs
The G12 can output a variety of NMEA messages and Ashtech’s NMEA-style
messages. Standard NMEA messages are output as a string of ASCII characters
delimited by commas, in compliance with NMEA 0183 Standards (version 2.2).
Ashtech’s NMEA-style messages are also output in a comma-delimited string of
ASCII characters, but may deviate slightly from NMEA standards. For example,
the maximum length of a standard NMEA message is eighty characters, but the
length of some Magellan messages goes beyond eighty characters.
G12RevD.book Page 33 Tuesday, April 2, 2002 4:33 PM
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