[GRASS-user] Extract single pixels with r.mapcalc?

[Glynn Clements]

LeventB wrote:

> Based on one raster map, i want to create a new map containing only eight
> cells - four in the corners of the map and four on the middle of the edges -
> with the category „1”. All other cells are supposed to be NULL-cells.
> I thought about doing this via r.mapcalc - yet i do not know if there is any
> possibility to manipulate only single cells with this command.

It's possible, although r.in.xyz may be a better choice.

To do it in r.mapcalc:

eval `g.region -g`
r.mapcalc <<EOF
outmap = if((row() == 1 || row() == $rows/2 || row() == $rows) && \
            (col() == 1 || col() == $cols/2 || col() == $cols) && \
            !(row() == $rows/2 && col() == $cols/2), 1, null())
EOF

-- 
Glynn Clements <glynn at gclements.plus.com>