[GRASS-user] r.terraflow crashes

[Markus Neteler]

On Sun, Jan 3, 2016 at 11:55 PM, Ken Mankoff <mankoff at gmail.com> wrote:
>
> On 2016-01-03 at 15:46, Anna Petrášová <kratochanna at gmail.com> wrote:
>> I don't have any experience with r.terraflow, but try using
>> r.watershed.
>
> Crashes with different errors. I'll post about that later. I was using terraflow because it claims to be for large data (not that I think this data is particularly large...)

r.watershed deals quite well with large datasets, too.See

https://grasswiki.osgeo.org/wiki/GRASS_GIS_Performance#Large_raster_data_processing
(r.watershed on a 90k x 100k pixels raster map)

> r.mapcalc 'phi = bed*2' does produce a data file, full resolution or downsampled.
>
> Oddly, "2*bed" works, but "2.5*bed" does not work.

That's rather unusual, indeed.

> Does r.mapcalc only do integer math?

Definitely yes.

> Not according to the manual.

Oh - so we should improve that:
https://grass.osgeo.org/grass70/manuals/r.mapcalc.html

Please let us know where to add extra explanations (what did you look
for and didn't find?)

> "r.info bed" shows the range is -5028 to 3678.

Please note that if "bed" is an integer map, r.mapcalc will generate
integer from "bed * number". You would need to write

2.5 * bed

or

1.0 * bed * 2

to get floating point results.

Should we expand this section?
https://grass.osgeo.org/grass70/manuals/r.mapcalc.html#floating-point-values-in-the-expression

Markus