[GRASSLIST:2114] Re: [Fwd: re: r.mapcalc]

[Eric G. Miller]

Perhaps you didn't understand our offlist discussion?  My comments to
your query were already posted to the list (and only the list) -- that's
how you got them ;) No need to repost...

On Wed, Jul 18, 2001 at 10:47:43AM +0800, Rohan Sadler wrote:
> On Tue, Jul 17, 2001 at 12:04:13PM +0800, Rohan Sadler wrote:
> 
> > > Dear GrassList,
> > > 
> > > I have just started on Grass last week and am using ver 5.0beta11 on 
> > > redhat 7.1.
> > > 
> > > r.mapcalc does not work for me so that any expression such as
> > > 
> > > test3 = test2 - test1                    (with test2 set as MASK)
> > > test3 = if(test2 != test1, 1, 0)
> > > 
> > > returns just the intersection of test2 and test1,
> > > and not what I want - which is that part of test2 that does not include 
> > > test1 (i.e. test2 minus the intersection).
> > > 
> > > If anyone has any ideas before I reinstall GRASS please forward them.
> 
> 
> Nothing wrong with r.mapcalc by your description. 
> 
> 1. Make sure to set the region appropriately "g.region rast=test1,test2"
> 2. Read the part of the manual page dealing with NULLs and the various
>    related functions/tests.
> 3. Remove the MASK (otherwise you'll get nothing).
> 4. Try "$ echo 'test3 = if(test1, null(), test2)' | r.mapcalc"
> 
>    Which translates to:
> 
>       if "test1" is not null, output null
>       otherwise output test2.
> 
> Alternatively, if I understand correctly, you could set the MASK using
> test1 and just "echo 'test3 = test2' | r.mapcalc".  I think that should
> work to get all of test2 that doesn't intersect with test1.
> 
> -- Eric G. Miller <egm2 at jps.net> <mailto:egm2 at jps.net>

-- 
Eric G. Miller <egm2 at jps.net>