[GRASS-user] v.breach and v.line.center GRASS addons

[Maciej Sieczka]

Hi

I have submitted 2 new scripts for GRASS 6.x to GRASS WIKI
http://grass.gdf-hannover.de/wiki/GRASS_AddOns:

v.line.center creates a points vector map with each point located in
the middle of the length of one input vector line.

v.breach creates vector maps of lines and points of continously
lowering elevation down the input watercourses, based on the input
raster DEM.



v.line.center is a simple self-explanatory tool.

v.breach is more complex. It is similar to r.carve -n, with the
following differences:

1. It takes the direction of input vector lines into account; which
means it is less prone to artifacts in the input DEM but more demanding
to input watercourses. As a result you can breach DEM even against the
slope, if that's needed ;).

2. It does not breach the DEM itself, but outputs vector points which
have the breached elevation attribute stored in the table. These points
can be used as additional data for interpolating more hydrologicaly
sound DEM from scratch, or rasterized and burned into the input DEM
manually (v.to.rast, r.mapcalc).

3. It also outputs vector lines, which are the input vector
watercourses segmented one segment per each DEM cell through which a
given input watercourse flows. Those segments have the breached
elevation attribute same as the output vector points. I needed such
output for my work. Maybe it will be of some use for others.

4. It is way slower than r.carve. Shell (I have got rid of bashisms I
hope) + Awk + standard UNIX tools.

See the v.breach manual for more details.

Maciek