Michael,
can you add those scripts with links to the Wiki add ons?
http://grass.osgeo.org/wiki/GRASS_AddOns
those are very useful modules and they could save some people time re-
inventing
what has already been done,
thank you,
Helena
Helena Mitasova
Associate Professor
Department of Marine, Earth
and Atmospheric Sciences
1125 Jordan Hall, Campus Box 8208
North Carolina State University
Raleigh NC 27695-8208
http://skagit.meas.ncsu.edu/~helena/
On Nov 16, 2009, at 5:07 AM, vetter michael wrote:
We already did a method to derive river centerlines based on
r.thin and a method to calculate cross sections (see the scripts).
It is not a method to derive the flow line of the river, but you
can calculate the center line of the river.
For those you need a very precise water surface polygon. To derive
such a high quality water surface you need a ortho image or a good
DTM like a 1m LiDAR DTM. By doing a classification using region
growing of height differences and the slope.
you can check out the scripts here:
centerline: http://www.uibk.ac.at/geographie/personal/vetter/
scripts/v.centerline.sh
smoothline: http://www.uibk.ac.at/geographie/personal/vetter/
scripts/v.smooth.tar
crossprofile: http://www.uibk.ac.at/geographie/personal/vetter/
scripts/v.crossprofile.tar
The sand or gravel banks are really a big problem in deriving a
water surface. Such a solution is presented in:
Höfle, B., Vetter**, M., Pfeifer, N., Mandlburger, G., Stötter, J. *
(2009)*: Water surface mapping from airborne laser scanning using
signal amplitude and elevation data. Earth Surface Processes and
Landforms, p. 1635-1649. DOI:10.1002/esp.1853.
good luck,
Michael
Thomas wrote:
If you come from a hydraulics background… one very
important need is the ability to generate channel
cross-sections interactively for, say, HEC-RAS and then do
flood inundation mapping from HEC-RAS from the modeling
results — I would think this would be a huge
contribution.
to get a good cross section you need to set it perpendicular to
the river's
center line. Which means you need a good river centerline. Which
means you
have to deal with the "river mile problem".
raster tools are not always good here as the river can be very thin
compared to the overall length leading to untenable resolution
settings
to get an good result. (r.cost + r.param.scale to pull out the cost
ridges or r.slope.aspect to pull out the maxima from the 1st
derivative
of the cost works, but the resolution issue gets ya)
any thoughts? some sort of reverse v.buffer?
small islands within the river also cause havoc with many
computational
approaches.
Hamish
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