[GRASSLIST:5142] Re: Raster crop/mask.

[Glynn Clements]

DzZero wrote:

> I have setup GRASS 5.0 and all seems to be working perectly.  I have 
> determined how to create a new project and import vector (dxf) and 
> raster (8bit tiled TIFFs) layers. Now I am trying to determine how I 
> might be able to draw a polygon and import one dxf (known) then use that 
> polygon as a mask or cropping line then in turn right out the area still 
> visible of the TIFF.

First, either:

a) use r.in.poly to import a polygon definition directly as a raster
map, or

b) use one of the v.in.* programs to import a file as a vector map
then convert it to a raster map with v.to.rast.

Then, to use the raster map as a mask, copy it (or rename it) to
"MASK", e.g. "g.copy rast=mapname,MASK".

Finally, to create a masked version of an existing raster map, use
r.resample.

> I am also curious about rotation and transformation 
> (2d) of the rasters.

r.proj will transform rasters between coordinate systems, while
i.rectify performs image rectification.

-- 
Glynn Clements <glynn.clements at virgin.net>