The methods of i-MAX and Virtual Reference Station (ViRS) are similar. Both are classed as individualized that require the rover to send an approximate position to the server. The relationship between the server and the rover for i-MAX and ViRS are shown in Figures 3 and 4 respectively.

Both methods use unpublished algorithms to generate Network RTK corrections and are therefore non-standardized.

In both methods the server calculates the network solution to reduce the distance dependent errors. This means the network solution is not optimized for the rover’s position and might be limiting the RTK solution.

Both methods generate RTK corrections that simulate single reference RTK. This limits the satellite data made available to the rover, therefore risking that in certain circumstances an RTK solution will not be possible.

The i-MAX and Virtual Reference Station methods are similar, but not identical. The major point of difference is that the i-MAX method generates corrections for a real reference station instead of a virtual reference station.

The i-MAX corrections are related back to a master station. This means that the bas eline between the master station and the measured point can always be directly re-measured. Therefore, the measurements are traceable and repeatable (Fig 3).

With the Virtual Reference Station method the rover does not receive any observations related to a real reference station. This means that the baseline between the virtual reference station and the measured point cannot be directly re-measured. This violates the fundamental surveying principles of traceability and repeatability (Fig 4).

The Virtual Reference Station corrections are optimized for the rover position at the beginning of the RTK session (i.e. after connecting to the Network RTK service). If the rover then moves a considerable distance within the same session (i.e. without disconnecting and reconnecting) the corrections might not be appropriate for the new rover location (Landau et al., 2003).

To resolve this issue, the user can disconnect and start a new session to generate a new reference station, or the server may automatically generate a new reference station. However, (in either case) generating new reference stations can cause jumps in position and accuracy. Therefore, the user can end up with inconsistent positions and accuracies throughout their survey.

In contrast, the i-MAX corrections are dynamically updated to follow the movement of the rover. In addition, i-MAX corrections are related back to a real reference station (the master station). This means that the resulting positions and accuracies are consistent.