[GRASS5] [bug #3704] (grass) d.rast.arrow does not save a line in the monitor history

[Hamish]

[d.rast.arrow too cluttered to be useful]

> > g.region rast=source_map
> > d.rast source_map
> > g.region res=  (res * 16)
> > d.rast.arrow ...
> > 
> > perhaps that leads to aliasing problems?
>
> This seems to work, but it is clunky. I could of course script a way
> to change resolution, display arrows, and change it back again.
> However, I wonder if this is desirable enough, when you make your
> improvements to d.rast.arrow, that it is worthwhile to include a
> (temporary) resolution setting in the module itself?

Done & in CVS.

d.rast.arrow now can take a raster map for arrow magnitude and there is
a new skip option to only draw arrows every Nth cell.

screenshot showing raster elevation level, with arrow direction and size
controlled by aspect and slope maps (created with r.slope.aspect); skip
factor set to only draw every third cell; and grid color set to "none":

  http://bambi.otago.ac.nz/hamish/grass/d_rast_arrow_magnitude.png


The question remains what to do if fed negative magnitudes. Right now I
have it skipping over that arrow (as it does for NULL values), but it
could take the absolute value or rotate the arrow 180 degrees.


enjoy,
Hamish