Specifications

Differential and RTK Operations 43
Differential and RTK
In the case of CPD with RTCM 18 & 19 or 20 & 21, if the message is partially received, for enough
satellites to compute a position, the age increments, but a position solution is still derived, and
continues to be output even if MAX AGE is reached.
Differential Accuracy vs. Base Data Latency
Figure 2 shows the growth of position error with increasing latency for DGPS.
RTK Accuracy and Update Rates vs. Base Data Latency
With an RTK remote you may choose between:
1. Higher accuracy and lower update rates (Synchronized RTK)
2. Lower accuracy, low latency, and higher update rates (Fast RTK)
Lower RTK accuracy still means centimeter-level accuracy
Use the command $PASHS,CPD,FST,ON/OFF to switch between the two modes.
Synchronized RTK
In this mode the remote receiver’s update rate is equal to the rate at which it receives
type 18, 19, 20, 21, or DBN messages. (Maximum of 1Hz). The latency of position is
approximately equal to the latency of the base-remote data link. Typical accuracy is
0.5cm+1ppm (1σ horizontal), and is independent of the rate at which the receiver
receives type 18, 19, 20, 21, or DBN messages.
Figure 3.2: DGPS Accuracy