[GRASS-user] r.to.vect problem

[Hamish]

Tyler Smith wrote:
> On Thu, Feb 08, 2007 at 06:50:01PM -0400, Tyler Smith wrote:
> > I thought it would make sense to convert each map to a shapefile,
> > and then get the overlap with v.overlay. However, r.to.vect doesn't
> > appear to allow for selecting a range of values to turn into an
> > area. Is there a way to do this? 
> 
> Aha! Since sending this first message I have discovered that my new
> favourite function, r.null, can be used to 'NULL'-ify the 0-5 part of
> my raster, making the rest available for vectorization. So I've got my
> answer, and can continue working toward the ultimate solution.


you can also use r.mapcalc to make a MASK map if you don't want to
modify your raster map.

r.mapcalc "MASK = if(oldmap > 5)"

"g.remove MASK" when done.

or,

r.mapcalc "newmap = if(oldmap > 5, oldmap, null() )"
# if( this, then use this, otherwise use this )


rasterintro.html needs something added to it about raster MASKs...


Hamish