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.Task
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.Problem
How do I get the data into GRASS?
James,
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 s.surf.idw 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 v.in.ascii.
If you want to use them in the cost surface analysis, you'll need to
rasterize them using v.to.rast. Read the manual entries for those commands
check out the ftp site (moon.cecer.army.mil).
Good luck.
Ishmael Williams
US Army Corps of Engineers
Fort Worth District
email: ish@alla.pl.swf.usace.army.mil