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

[nikos ves]

On Wed, 2010-06-16 at 21:49 +0300, Micha Silver wrote:
> You can also try a different approach. You mentioed that you already 
> have a raster of slopes and you want vector polygons (? is that your 
> goal?) covering everywhere with slope >40.
> You can run the GRASS module r.mapcalculator, select the slope raster 
> for  raster A then enter A>40 in the equation text box.
> The result will be a raster of slopes, but only greater than 40.
> Now do r.to.vect to convert to polygons... 

I agree, that will take much less time. 

Contour function for me always takes huge amount of time for me,
especially if its complex, like slope.

There are unlimited ways to extract information from data, you just need
to use your imagination and be a little patience until you learn your
way around!  

Qgis also has a map calculator plugin as well. You can find it, as
always, using the plugin manager
-- 
nikos ves <vesnikos at gmail.com>