Navman 20 GPS Receiver User Manual


 
LA000577C © 2006 Navman New Zealand. All rights reserved. Proprietary information and specications subject to change without notice.
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Unused messages
Input messages where the message ID is not between 100 and 255, or where the message
ID does not correspond to a specied function, result in the response:
$PTTK,INVALID*CS
Errors
Errors in message receipt (other than checksum errors) result in the response:
$PTTK,ERROR,xx*CS
where xx is a hexadecimal error code.
Magnetic Variation (Declination)
The Jupiter 20 module calculates the magnetic variation (the Jupiter 30 does not).
Magnetic Variation elds in $GPRMC
The last two elds in the message $GPRMC are the magnetic variation. An Easterly variation
should be subtracted from, or a Westerly variation added to, the true heading to give the
magnetic heading (the heading given by a magnetic compass).
For example, the output might be:
$GPRMC,220137.250,A,4331.9077,S,17238.2308,E,0.075949,168.82,071004,23.1,E*4C
Standard SiRF output:
$GPRMC,220137.250,A,4331.9077,S,17238.2308,E,0.075949,168.82,071004,,*17
Magnetic Heading eld in $GPVTG
The third eld in the message $GPVTG is the magnetic heading (denoted by the ‘M’ in the
following eld). This is the heading that would be reported by a magnetic compass.
For example, the output might be:
$GPVTG,168.82,T,145.70,M,0.08,N,0.14,K*41
The standard SiRF output:
$GPVTG,168.82,T,,M,0.08,N,0.14,K*58
3.3.3 Altitude output
The module outputs the correct altitude and geoid separation in the $GPGGA NMEA
message. Most SiRFstar-based modules output the height above the current datum (usually
WGS84) ellipsoid as the altitude, contrary to the NMEA specication, and older modules
omit the geoid separation. The Jupiter receiver outputs the height above mean sea level, as
required by the NMEA specication.
For example, the output might be:
$GPGGA,220137.869,4331.9077,S,17238.2308,E,1,06,1.6,61.7,M,11.3,M,0.0,0000*55
Standard SiRF output (v2.3 and earlier):
$GPGGA,220137.869,4331.9077,S,17238.2308,E,1,06,1.6,72.0,M,,M,0.0,0000*6D
Or (v2.3.1 and 2.3.2):
$GPGGA,220137.869,4331.9077,S,17238.2308,E,1,06,1.6,72.0,M,11.3,M,0.0,0000*50