[GRASS-user] [GRASSLIST:1183] how to rotate raster in GRASS ? ArcGIS better than GRASS ?? I hope NO!!

[Glynn Clements]

Maciej Sieczka wrote:

> > Yes, unfortunately I have to rotate a DEM for a specifica angle so do a 
> > transposition is not a good method.
> > I kwon ArcGIS can rotate DEM but I hope this thinks is possible also in 
> > GRASS...
> 
> I haven't thought much of this, but how about r.to.vect feature=point
> -> v.transform zrot=angle?
> 
> On the other hand, something tells me you should be able to rotate
> raster using r.mapcalc alone (a guess).

No. r.mapcalc doesn't let you access arbitrary cells from the input
map, only the cell corresponding to the current output cell,
optionally offset by a fixed displacement.

Rotation can't be done with any program which uses the normal
top-to-bottom access strategy (which includes r.mapcalc).

AFAIK, the only way to (directly) perform arbitrary rotation is with
i.rectify.

-- 
Glynn Clements <glynn at gclements.plus.com>