reprojection of rasters

Markus Neteler neteler at
Fri Apr 21 06:03:56 EDT 2000

On Thu, Apr 20, 2000 at 11:18:42AM -0600, twiens wrote:
> I'm fairly new to GRASS so this may have been discussed earlier on the
> list serv. Sorry if I'm repeating a common question. I can't find any
> obvious methods for reprojecting rasters. What I've done is import the
> raster, convert to a vector and then reproject the vector and finally
> convert the vector back to a raster.
> Is there a more elegant method of doing so? Does this method introduce


you can reproject in different ways:

 - i.rectify: using control points on a map reference, linear (affine
      transformation), 4 points required in maps corner
 - i.rectify2: using control points on a map reference, non-linear
   (polynomial transformation). The number of control points required for a
   selected order of transformation (represented by n) is 

    ((n + 1) * (n + 2) / 2) 
   [for a 3rd order transformation you need at least 10 control points)

 - r.proj: reprojects using GRASS internal projection software (PROJ4).
   No control points needed. Limitation: currently transforms full
   locations only. If you just need a map portion, create a new smaller
   location first before transforming into new location (with other

The i.rectify* commands are for satellite images etc., r.proj (v.proj)
for maps.

See the man pages for details:

 Kind regards

   Markus Neteler

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