ashtech GG Surveyor, Reference Manual

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GPS and GLONASS Concepts A-7
GPS and GLONASS
corrections are message types l and 9. Similar messages for GLONASS differential
corrections are message types 31, GLONASS equivalent to GPS message type 1, and
GLONASS type 34, GLONASS equivalent to GPS message type 9.
Other RTCM messages carry information about reference station parameters, satellite
health, etc. These have been defined for both GPS and GLONASS.
Other messages are being developed to improve further the operation of
GPS+GLONASS systems in differential mode. A GLONASS-GPS time offset
message has been proposed, which allows the reference station to report the time
offset between the two systems so that the GPS+GLONASS receiver does not have to
calculate it. See $PASHQ,DUG on page 80 for more information. Table 1.2 lists the
RTCM SC-104 messages for GPS and GLONASS, which the GG Surveyor supports,
both as a reference station and a rover.
NMEA 0183
The National Marine Electronics Association Standard NMEA 0183 defines
interfacing standards for marine electronic devices. The following messages apply
specifically to GPS, and are supported by the GG Surveyor.
• GGA—Global positioning system fix data
• GSA—GPS DOP and active satellites
• GRS—GPS range residuals for each satellite
As of January 1997, the NMEA 0183 Standards Committee was in the process of
finalizing the definition of messages for GLONASS information. When these
messages are finalized, Ashtech will comply with NMEA GLONASS standards in the
GG Surveyor. For more information on NMEA messages and decisions, see the
NMEA web page, http://www.coastalnet.com/nmea/.
Table A.2: RTCM SC-104 Messages for GPS and GLONASS
Parameter
GPS
Message Type
GLONASS
Message Type
Differential corrections 1 31
Reference station parameters 3 32
Null frame (filler) 6 6
Partial satellite set differential corrections 9 34
Special message 16 36
RTK Uncorrected Carrier Phases 18 19
RTK Uncorrected Pseudoranges 19 19
Extended reference station parameters 22 22