ImpulseRadar PinPointR User Manual V1.5
Page 33 (36)
Appendix C
–
GPS
How RTK Works
RTK involves a stationary base station and one or more mobile GPS receivers, also known as rovers.
Provided that the base station has continuous line-of-sight to each rover, it transmits GPS corrections
to each in real-time using radio waves. If a sufficient number of satellites are visible, RTK can provide
a fixed position within a fraction of an inch. If insufficient satellites are visible, RTK can provide only a
float solution, with a precision of a few inches.
Fixed RTK
RTK uses a complicated mathematical formula or algorithm to calculate the exact number of radio
wavelengths between the satellites and the base station system -- a process known as ambiguity
resolution -- and yield either a fixed or float solution. In a fixed solution, the number of wavelengths is
a whole number or integer, and the algorithm is constrained to yield a whole number. A low number
of visible satellites, poor satellite constellation geometry, and a week radio link between the base
station and the rover may prevent a fixed solution.
Float RTK
In a float solution, the algorithm does not yield an acceptable fixed solution, so the ambiguity is allowed
to be a decimal or floating-point number. According to Tripod Data Systems, a float solution typically
generates precise coordinates to between 4 and 18 inches over a known distance between two points
of just over half a mile. If a float solution is the only solution available, it may be possible to reinitialize
an RTK system, or wait, for a more precise fixed solution. However, if poor satellite visibility is to blame,
a fixed solution may be unavailable.
Considerations
The precision of RTK data collection depends on the distance between the base station and the rovers,
so it's desirable to keep the distance between them to less than 6 miles. RTK systems are available in
single and dual-frequency versions; dual-frequency versions are typically faster, more precise and
operate over longer distances than single frequency versions, but they are correspondingly more
expensive.
Figure 31
External GPS diagram and wiring arrangements
