[GRASSLIST:3464] Re: r.thin

[Morten Sickel]

On Saturday 06 April 2002 21:16, you wrote:
> This is my first post on this mailing-list, excuse my english and my absurd
> questions. I'm a GRASS-newbie :-)
No problems with your English, just relax! We've all once been newbies..

>
> I'm trying to convert a large and complex raster (TIFF) in vector format.

Been there done it..
>
But
> The vector map obtained is really "strange".
> It contains a kind of "trees" of vectors. These trees are starting from all
> nodes of raster "lines" and goes in any directions, but not in those of the
> raster "lines".
>
> Thus, I've a vector map that is not similar at all at the original raster.
>
Have a look at the map produced by r.thin, that should be quite similiar to 
your original map. If not, what might have happened is that r.line has picked 
up your background rather than the foreground. If you have a black and white 
image, use r.mapcalc to switch 0 and 1 in your map. If you have a multiple 
color map, you must define the right areas (colour) as background (I don't 
remember, they (r.thin and r.line) either take 1 or 0 as  background).

Hope this helps, I once had the same problem my self. 

Morten

-- 
Morten Sickel
GIS Consultant
Drøbak, Norway