[GRASSLIST:2110] re: r.mapcalc
Eric G. Miller
egm2 at jps.net
Tue Jul 17 00:40:27 EDT 2001
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
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>
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