Trimble Pathfinder to GRASS

ish at ish at
Wed Aug 20 08:00:00 EDT 1997

>        I've wandered over a block of land with a Trimble Pro XR DGPS
>        generating 6327 data points following roads, fences and other
>        interesting features.  The data is accurate to .75m - it was
>        real-time differential corrected.  The data includes elevation.
>        I've installed GRASS 4.1 on a DIGITAL UNIX system and a DEC
>        Ultrix system.
>        Plot the path of a proposed access road so as to minimise cost
>        of construction and cost of maintenance.  The road should be
>        short enough to be cheap, and yet not so steep as to cause
>        maintenance problems after the five yearly heavy-rainfall event.
>        I am buying the block of land to live on, moving out in two
>        years, and I'd like to take a first cut at this path before
>        I involve road contracting surveyors.
>        How do I get the data into GRASS?


Sounds like it might be a job for "r.cost", a raster based program
for computing the cost of moving across different locations based
on weighted surface values (ie. slope, hydrology, obstacles, etc.).
You'll need to use to extrapolate an elevation surface
from the elevation point (site) data; then run "r.slope.aspect" to
derive the slope and aspect files from elevation. I would be cautious
about the accuracy with the GPS-derived elevation data however even
with differential correction. You can view the elevation raster surface
in 3-D using d.3d and see if it is suitable for your analysis. The
programs r.neighbors and r.mfilter might help smooth data irregularities.
Your region is small enough that you can set the cell resolution for
your data pretty low (1-5 meters?). You might find a need for line of
sight assessment (ie. what areas are visible from a selected point)
using r.los.  You can view the 

The other date (roads, fences) can probably be imported using
If you want to use them in the cost surface analysis, you'll need to
rasterize them using Read the manual entries for those commands
check out the ftp site (

Good luck.

Ishmael Williams
US Army Corps of Engineers
Fort Worth District
email: ish at

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