[GRASSLIST:62] Re: Creating axis of a river

[Hamish]

> Hamish i am testing your procedure,

Again, I'm not sure how to do this with vector-only solution, and I
don't think it is appropriate to use at a 10m raster resolution when 
the river is 30m wide. You error will always be half the width of the
river.. not acceptable.

I was using it for looking at the width of fjords 1km wide, there it
works fine as +-10m isn't a big deal.

Maybe do a small section of the river at a time at 1m resolution?

> but i don't uderstand what is this line for:

> r.grow in=regional_bound out=regional_bound_grown1 old=1 new=1
> 
> what is regional_bound file?

That is one of my maps, used as both a cost and a MASK map. That map
only covers the sea area. r.grow spread it out in all directions by one
cell, so starting points (the coastline) are always inside the MASK
region. Before for my data 50% of the time the coastal points were 1
cell on land side and ignored. I wanted the final map to be all "1"
values. (cost to move to next cell is 1)


alternate (still raster step) solution:

Change lines to boundaries (v.type); load into v.digit and make lines
into a closed area, add a centroid. Make sure centroid has a category
number (v.category). Then v.to.rast, r.thin, r.to.vect.


Hamish