[GRASSLIST:4381] mapcalc or ???

[J.c.m. van der Kwast]

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?

Greetings Sjors