[GRASSLIST:35] Creating Axis of a river...

[Luca Casagrande]

Hi Hamish!
I can take out the z-values, so now I need to found the midline in the 2d 
space.Can this be done in simplest way?

Thx for your support
Luca

> ok, you are starting already with lines, not area boundaries, so no need
> to turn boundaries into lines with v.type. (v.extract only works on
> features with a category, thus v.category.) You can go to the v.to.rast
> step directly, make a "one" map for the cost,
>
> r.mapcalc cost_map=1
>
> then do r.cost -k, 'r.param.scale param=slope size=7', threshold at
> about 30 degrees with r.mapcalc, r.thin.
>
> bonus: river width at any point is possible by using r.mapcalc to make
> r.thin map have cost's values * 2, then r.grow out to the edges.
>
>
> BUT, looking at your data, the river is 30m wide so a 10m raster
> resolution would make the output too coarse so this method is pretty
> bad. Maybe ok if you used 1m resolution on a small section but
> not practicable for the whole area.
>
> You need a vector solution for figuring out river width, someone else
> will have to help you with that.



Hamish
-- 
"E' molto più bello sapere qualcosa di tutto, che tutto di una cosa (Blaise 
Pascal)."

GENTOO-GIS Development Team
jabber: casagrande at jabber.linux.it