ashtech GG Surveyor, Reference Manual

Page: 83 / 256

Differential and RTK Operations 65
Differential and RTK
Auto Differential Mode
When a user operates a rover receiver in differential mode (either code phase or
carrier phase), a failure at the base station or in the data link causes the rover receiver
to cease outputting differentially corrected positions. Auto differential mode allows
the user to output an autonomous position at the rover receiver if differential data
from the base station is unavailable. Auto differential mode is enabled by entering the
command $PASHS,RTC,AUT,Y. Table 5.10 describes how auto differential mode
affects position output at the rover receiver.
RTCM Messages
The GG Surveyor accepts RTCM 104 version 2.1 differential formats. The GG
Surveyor is set to differential mode in any of the serial ports with the set command
$PASHS,RTC,str,c where str is BAS or REM and c is the port. Of RTCM message
types 1 through 64, the GG Surveyor processes only: types 3, 16, 22, 32, and 36 for
station location and special information; types 1, 2, 9, 31, and 34 for RTCM
differential corrections, null frame type 6 and 34, and RTK data message types, 18
and 19. The differential corrections are automatically processed by the GG Surveyor.
RTCM message types 3, 16, 22, 32, and 36 provide user information from the
Table 5.10: Auto Differential Modes and Position Output
Mode Position Output
Code differential
Auto Differential Off
(Default code mode) Differential position output if the age of corrections is less than maximum
age (maximum age as defined in the rover by $PASHS,RTC,MAX,xx).
No position otherwise.
Code differential
Auto Differential On Differential position is output if the age of corrections is less than
maximum age, otherwise an autonomous position is output.
Carrier differential
Fast CPD On
Auto Differential Off
(Default carrier mode) Once the rover mode has been enabled, autonomous position outputs until
it has computed the first CPD position. A CPD position solution continues
to output until the age of corrections is greater than the maximum age.
Carrier differential
Fast CPD On
Auto Differential On Once the rover mode has been enabled, autonomous position outputs until
it has computed the first CPD position. A CPD position solution continues
to output until the age of corrections is less than the maximum age,
otherwise an autonomous position is output.
Carrier differential
Fast CPD Off
Auto Differential Off or
On Once the rover mode has been enabled, autonomous position outputs until
it has computed the first CPD position. A CPD position solution continues
to output until corrections stop, and no position outputs unless corrections
are available.