[GRASS-user] r.param.scale Incorrect Output

Hamish hamish_b at yahoo.com
Thu Jan 28 23:23:13 EST 2010

Rich wrote:
> >  I'm stymied trying to get output from
> > r.param.scale that is equivalent to
> > the example on the bottom of the man page.

even using the Speafish dataset?

>   Resetting g.region to the input elevation map
> without any additional options and adding a zmult
> factor of 5 appears to help.

It may be (just guessing here) that the module assumes that the x,y 
and z values are all using the same units (eg all meters or all feet).

in that case a zmult of 3.28 would get you pretty close. how reliefy
your area is probably makes a bit of a difference as well.

> When the specified param is 'features' I see what should be ridges
> and channels, but no peaks or pits.

should it have them? (ok, Oregon is for the most part a fairly hilly pace,
it probably should). but if you were looking at a floodplain it might not.

see feature.c and param.c in the source for the formulas used.

maybe it is artificially flat: if it isn't already try using the zscale=
option or r.mapcalc to make z match x & y scale units.

>   Changing the calculated param to either elev or
> profc yields blank maps
> when I try to display them with d.rast.

sometimes the colors can be misleading. check with r.univar and if
needed rerun 'r.colors -e' to be sure.



More information about the grass-user mailing list