[GRASSLIST:4382] Re: mapcalc or ???

[Eric G. Miller]

On Mon, Aug 26, 2002 at 05:16:10PM +0200, J.c.m. van der Kwast wrote:
> Hi,
> 
> I'm wondering on how to solve a problem, which is the following. I have 
> a simple (raster)map with one irregular shaped object (lets say field) 
> of interest (cat1, everything else=0).
> How to divide this field into strips of one cell wide in the same 
> direction, eg north to south or east to west and vice versa, each 
> representing a different cat?
> I've been playing around with mapcalc and with the help of the doc's 
> I've succeded in growing a border of one cell and even a strip of one 
> cell representing the for example the north side of the field. Then 
> growing a strip of one cell to the south and give it a new value I can 
> manage, but dividing up the whole field is beyond me.  Any suggestions?

Perhaps you want the row() function, coupled with isnull()?

output = if (isnull(input), null(), row())

If you want rows to start from 1, afterward, find the mininum
value and then subtract:

output2 = if(isnull(output), null(), output - <constant>)

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