Chapter 3	GrafNet

About unfixable data

Moving Antenna

An antenna that is not still causes havoc with static processing. This can be caused by an operator not holding the antenna still, heavy winds or a vehicle that is rocking. Theoretically, this data should be processed as kinematic and the position solutions averaged but GrafNet does not currently support this mode of processing so this data should be avoided. If it needs to be processed, a float solution will perform best.

Ionospheric Effect

Heavy ionospheric activity can cause large carrier phase noise. A single frequency receiver cannot do much to alleviate the problem. However, dual frequency data will most likely process better with an iono-free solution rather than some of the fixed integer techniques, such as the fixed solution.

Constant Loss of Lock

Antennas placed under trees or similar obstructions will often continuously lose lock, which causes the fixed static to fail and the float solution to report poor accuracy.

Poor Antenna Location

High multi-path mostly affects the C/A code but the carrier phase can also be affected and might cause a fixed solution to fail. Antennas placed near large metal structures are most affected. Locations on rooftops can also cause poor data. Avoid these locations. The only suggestion for possibly improving this data during processing is to reduce the size of the C/A code standard deviation from within the Measurement tab of the processing options.

Receiver Problems

Sometimes a GPS receiver just collects bad data. Low power or a poor antenna connection can cause this. If the problem is consistent with a particular GPS receiver unit, have the manufacturer check the GPS receiver.

3.2.2Unfixable Data

Sometimes data is simply bad and changing the options cannot help. This section discusses some of the possible causes of such data in the shaded box. For some cases, there is advice for improving the solution.

See Section 9.5, on Page 268 for help with static processing.

154	GrafNav / GrafNet 8.10 User Guide Rev 4