[Qgis-user] Re: How to draw a polygon shapefile around raster pixels?

[nikos ves]

On Thu, 2010-06-17 at 10:00 -0700, boesiii wrote:
> I tried using r.mapcalc with "slope_gt40_map=if(47001310ee>=40,1)" and all I
> get is a black raster and every pixel has a value of 1.
> 
> I also tried using r.mapcalculator with "A>40" but the resulting raster
> still has pixel values less than 40.
> 
> What is the correct code I should be using for either tool? 
With grass:
using the contour:

r.contour input=slope at slope output=valid levels=40 cut=0 --overwrite

Using the mapcalc:

r.mapcalc "valid_raster" = "( "slope at slope" > 40)"

*Pro tip: Before you start, set the resolution at about ~200m otherwise
you might not like the results-> g.region res=200 

-- 
nikos ves <vesnikos at gmail.com>