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What Is Difference Between RTK Fix & RTK Float?

Real Time Kinematic, or RTK, refers to a data collection method used for surveying based on the Global Positioning System, or GPS. The GPS relies on a network, or constellation, of 24 satellites that transmit signal information to Earth. Depending on the number of satellites visible in the sky at any time, RTK data collection can be ̶0;fixed̶1; or ̶0;float,̶1; with differing levels of precision.

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 antenna -- 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 poor 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 simply 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 it̵7;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.

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