Spectra Precision ProMark 800 Reference Manual - Manual (Page 99)

87
RTK Implementation
Time-Tagged RTK Output Mode
Principle. In Time-tagged RTK, the rover will compute and
output a single RTK position for each epoch of RTK correction
data it receives.
The time when position is requested is t0 and the time when
the rover starts providing the position for time t0 is t1. Times
t0 in the base and the rover are synchronous because they
originate from the same clock which is the GPS System time.
Here the latency (t1 – t0) is caused by data processing times
in both the base and the rover as well as the base-rover
propagation time, the latter being negligible compared to the
former. In this configuration, a typical latency time in Spectra
Precision receivers is about 100 ms.
Use Context. Time-tagged RTK should be used when
consistent accuracy is more important than the position
output rate and when a relatively long latency is acceptable.
Benefit. RTK positions are consistently accurate.
Drawback. Time-tagged RTK can be inconsistent in its output
because any interruption in the flow of RTK correction data
will cause the rover to cease outputting positions. An
interruption could be caused by a problem at the base or
Lat
enc
y
Lat
enc
y
Lat
enc
y
Epoch1 Epoch2 Epoch3
Pos1
RTK
Correction
Data (Base)
RTK Position
Output
(Rover)
Internal
Processes
in Rover
t0a t1a t0b t1b t0c t1c
Pos2 Pos3
Rover positions at times t0.. are delivered at times t1..
t0..: Position request times
t1..: Position delivery times
2. RTK correction data computed at t0.. arrives in rover
3. Rover computes RTK position from its raw data and the base’s correction data
1. Rover saves GNSS raw data received at t0..
2 3 1