That said, considering that a single WAAS/EGNOS fix now has an accuracy of <3m, perhaps any higher accuracy is unnecessary when compared to survey errors and the rate of spread of tectonic plates!
On the subject of ludicrous accuracy surveys, has anyone ever considered the curvature of the earth for a cave? My back of the envelop calculation suggests a 1m vertical error after 3.5km.
Firstly, how do you know for certain that the fluctuations are only time dependant? How many different factors are involved and how will they vary across time as well as space?
Given I have a GPS receiver which can connect to a serial port on my Windows laptop, what software can I use to capture the position data and time for data logging purposes?
If you have two it is possible to get decent accuracy by taking readings at a base station with a known location (trig pillar?) and at the cave entrance.
Given the feedback received, I will propose a Surface Mapping talk for HE2011
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