ashtech GG Surveyor, Reference Manual

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36 GG Surveyor GPS+GLONASS Reference Manual
Typical messages might be 20 to a maximum of 79 characters in length and
generally require transmission no more often than once per second.
• Proprietary
When specific information was needed, and the NMEA standard did not
contain a suitable message, Ashtech created proprietary messages in a
NMEA style format. Messages are available in ASCII.
• RAW
Raw Data outputs in binary format and includes measurement data,
ephemeris data, almanac data, and position data.
The receiver has two options which affect the rate at which data output: position
update rate and Raw measurement update rate. The highest output rate supported
under different conditions is 5 Hz.
5 Hz Output
The GG Surveyor, as an option, provides the capability of 5 Hz internal receiver
update rate, allowing raw data and NMEA data to be output every 0.2 seconds. Two
options are available to control this feature: the position update rate option for NMEA
output rate, and raw measurement update rate for raw data output. See “Receiver
Options” on page 4 for more information. Because of CPU power limitation, when
this option is set, the receiver will update at 2 Hz until command $PASHS,POP,5 is
issued. When updating at 5 Hz, the receiver will use only 16 satellites in the position
solution, although it will track all available satellites. During the period while 5 HZ
update is not required, you can revert to 2 HZ and use all available satellites in the
position solution by issuing the command $PASHS,POP,2.
NMEA Outputs
As an option, the GG Surveyor allows you to output NMEA message format and
other miscellaneous messages through the serial ports. The following standard
NMEA messages are available: GLL, GXP, GGA, VTG, GSN, MSG, GSA, GRS,
GST, RMC and ZDA. Additional non-standard messages are available: LTN, AIM,
POS, SAT, RRE, TCM, and TTT. All standard NMEA messages are a string of
ASCII characters delimited by commas, in compliance with NMEA 0183 Standards
Version 2.1. All non-standard messages are a string of ASCII characters delimited by
commas, in the Ashtech proprietary response format. Any combination of these
CAUTION
When collecting data at 5 Hz, because of large amounts of data being output
through the serial ports, a 486-66 MHz or Pentium™ computer with a fast
serial and parallel port card (i.e., 16550 serial and parallel card) is recom-
mended. The serial port baud rate should be set to a baud rate above 38K.