[GRASSLIST:3543] Re: Geophysical/Potential field modules for GRASS?
michael.barton at asu.edu
Sat May 29 11:50:11 EDT 2004
On May 28, 2004, at 10:25 PM, Hamish wrote:
> Sounds like a job for Matlab/Octave to me .. We don't get to lay nice
> grids over our study sites at sea (or manage to get the ship to go in a
> straight line anyway), so what I've done in the past is to log the NMEA
> output from a GPS into a laptop while our instruments spit out
> "1,time,date,value" style data which gets recorded into another
> A Matlab postprocessing script does a linear interpolation of position
> from the NMEA log for each data point, and directly writes a GRASS
> file. Any spatial interpolations of the data can then be done from
> there in the GIS. [It's not as hard as it might sound]
This seems like a very nice setup for your case. For the geophysical
survey I've had been involved with (admittedly limited), the scale is
too small for GPS to be of use unless high resolution differential
correction is applied (data points along transects separated by
centimeters and transects separated by a few meters). The grid is set
up in advance, however (a luxury you don't have at sea). So the xy
coordinate values have to assigned by 'dead reckoning' based on the
predefined transect grid. I haven't used Matlab or Octave, but I
suppose they could do this kind of transformation. It's pretty
straightforward in a spreadsheet. However, if this is the common way
this kind of work is done for magnetometry, resistivity, conductivity,
and GPR, then it would feasible to design some kind of pre-processing
module. What I don't know is the extent to which the ascii output from
the relevant data recorders used by different manufacturers is
sufficiently standardized so as to plug into such a module. If everyone
records 'new transect' and 'data point' in very different ways, this
could be difficult as you suggest.
> [*] all clocks sycronized to GPS time before hand of course
> If you already have a grid set out, you can skip all the GPS stuff &
> script is all the easier.
> I don't see how this could be implemented as a generic GIS module.
> Each job is custom..
C. Michael Barton, Professor
School of Human Origins, Cultures, & Societies
PO Box 872402
Arizona State University
Tempe, AZ 85287-2402
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