[GRASS-user] Transforming raster lines to vectors with correct segment attributes

[Moritz Lennert]

On 27/01/14 11:27, Johannes Radinger wrote:
> Hi,
>
> I have a raster river (processed with r.thin) which I want to transfrom
> to a vector.
> Therefore I use r.to.vect with the lines option. However, the raster has
> two different
> values representing e.g. habitat quality (good/bad) for single segments
> (group of raster cells). This information is written strangely to the
> vector attribute table as the lines
> are not broken at changes of habitat quality which is a reasonable
> behaviour of r.to.vect.
>
> As I need the attributes in my vector table I thought about splitting
> the vector into
> small segments (<raster resolution) and updating the attribute table
> with v.what.rast. However when I use v.split the attribute table of the
> created map still has the same number of entries than before. So what do
> I miss here to get single rows and thus categories for the single
> created lines from v.split?
>
> Or is there any other/better way for such transformation of raster lines
> to vector lines incl. an update of the attribute table?

I'm not sure I totally understand your problem (an example with the NC 
data would probably help), but have you tried the '-v' flag (Use raster 
values as categories instead of unique sequence) of r.to.vect ?

Moritz