[GRASSLIST:1218] Re: Combining raster layers with r.mapcalc

[Paul Kelly]

On Fri, 12 Sep 2003, Bill Dickinson Jr wrote:

> Hey there:
>
> In running through the SEEDS tutorial, one of the tasks is combining
> two raster layers into a single raster using r.mapcalc. The
> individual layers show the data properly, but the resulting combined
> layer contains no data. Here is what I do:

This is *probably* because the tutorial was written for GRASS 4.x where
there was no concept of a NULL value, only zero. In GRASS 5.x r.mapcalc,
where any part of the input maps contains no data, the output will have no
data. See here for a fuller discussion (and why the tutorial cannot be
updated):
http://intevation.de/rt/webrt?serial_num=1338

Maybe use r.patch instead?

Paul