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5700 GPS Receiver User Guide 95
Real-Time Kinematic (RTK) Surveying 8
Applications
The Synchronized RTK solution yields the highest precision possible
and suits low dynamic applications such as human-mounted guidance.
It is not as suitable for airborne applications, such as photogrammetry
or aircraft landing system calibration, which require update rates in
excess of 1 Hz. Data postprocessing can be used back in the office to
generate corrected results, but postprocessing can cause data
management problems, particularly for large data sets collected at 5 or
10 Hz.
Low Latency RTK
Latency in Synchronized RTK processing is largely due to the
formatting and transmission of the reference station data to the rover.
The 5700 receiver includes a Low Latency positioning mode for
applications that require centimeter-level accuracy almost
instantaneously. The Low Latency positioning mode delivers 5 Hz
position fixes with around 20 millisecond latency, and with a precision
that is only slightly less accurate than Synchronized RTK positioning.
In the Low Latency positioning mode, accuracy is considered less
important than timeliness. The Low Latency mode relies on the
predictability of the reference station phase data. Given past reference
station phase measurements, the 5700 receiver can accurately predict
what they will be in the next few seconds.
Instead of waiting for carrier phase measurements to arrive from the
reference station, the 5700 rover predicts or projects what the
reference carrier phase measurements will be for the current epoch. A
baseline solution is then generated using the projected reference
station carrier phase measurements and the observed rover receiver
carrier phase. The latency of the position solution derived from
projected carrier phase is around 20 milliseconds.
An increase in the data link delay causes an increase in the projection
time of the reference station phase data. This leads to an increase in
the uncertainty of the RTK solution. In many applications the slight
noise increase in the Low Latency solution is tolerable.