ashtech GG Surveyor, Reference Manual

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126 GG Surveyor GPS+GLONASS Reference Manual
or it is too old, the day number is taken as zero. If an adequate GLONASS almanac is
available, the receiver determines on which day within the range [-3 + N
A
, 3 + N
A
] the
satellite coordinates at t
b
based on the almanac data fit best with known ephemeris
coordinates.
The broadcast ephemeris from a GLONASS satellite does not contain the satellite slot
number. This information is derived from the almanac. When the GG Surveyor has
ephemeris data for a satellite but no almanac data (this occurs at startup, before the
almanac has been fully transmitted), the satellite number is set to zero. Once the
almanac has been received, the satellite number is updated.
SNV: Enable/Disable GPS Ephemeris Data
$PASHS,RAW,SNV,x,s
Enable/disable ephemeris data (SNV) messages on port x where x is the output port,
and s is ON or OFF.
Example: Enable SNV on port A
$PASHS,RAW,SNV,A,ON<Enter>
Ephemeris data is output once every 15 minutes or each time the IODE changes, whichever comes
first, with one satellite output at each recording interval (RCI).
$PASHQ,SNV,x
The associated query command is $PASHQ,SNV,x. This command outputs the GPS
SNV ephemeris data response message on port x, where x is the optional output port.
$PASHR,SNV
The response is one binary message per locked satellite in the form:
$PASHR,SNV,(ephemeris structure)
where Table 6.40 defines the measurement structure.
Table 6.40: SNV (Ephemeris) Structure
Field Bytes Content
short wn 2 GPS week number [0,...,1023]
long tow 4 Seconds of GPS week [0,...604799]
float tgd 4
Group delay (±127*2
-31
) (seconds)
long aodc 4 Clock data issue
long toc 4
Clock data reference time [0,...,604784] (LSB = 2
4
seconds)