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Simple Fortran Math Problem
I am asked to follow the path of a column using GPS in near real time and compare the results to some other results.
The GPS gives you an ASCII file with Easting, Northing, time etc in a standard form. Fortran can read it easily and do the trivial math.
This is the raw data from a simple GPS and it has not yet been post processed, with RTKLIB written in C. I was just looking at the raw.
A sample output from 8 hours of eastings yields
It is trivial to put it into XY but there is no need here, the ground theoretically covered is a line about 5 metres long, as noted here
If I collect the data over 2 days I get a mess like this
which is a 2.5 metre circle of data.
But now I have 80000 points, about 1 per second and the data is following a set of patterns related to the satellites and the screening with a period of about 4 hours, the question is how stable is the center and how long to do you have to record to get a stable center estimate.
But if I break the 80000 points into 10000 point sets and do math, I have covered the cycle period nicely each time and the results suggest about 1 mm of total movement, about what I would expect. The graph is in mm.
Am I merely seeing a manifestation of the central limit theorem?
Why are the GPS programs not written in Fortran, it is a pain.
I will look with RTKLIB now to see how close that gets.
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John,
Here is a suggestion.
Use two GPS sensors. One attached to your column, and one attached to bedrock (or as close as you can get).
Then subtract the same timed measure of the bedrock GPS sensor from the column GPS sensor.
IOW provide an "immovable" reference point as opposed to presuming the satellites provide a virtual fixed reference point.
Alternatively, you can use two precision optical range finders.
Jim Dempsey
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