[GRASS-user] unstable results with r.param.scale ?

[Vincent Godard]

Dear Grass users,

I've been using r.param.scale to compute various type of curvatures over 
a 1 m LiDAR DEM (FCELL) (from opentopography.org) :

r.param.scale --o -c input=dem output=curvature size=15 method=profc
r.info -r curvature

I usually get reasonable results like (checked with independent 
calculations) :

min=-0.203124601340989
max=0.0685868278408049

But when running this command repeatedly, I randomly (usually every 3rd 
or 4th time) get very different results like :

min=-127112309.998249
max=131128979.492382

I am running GRASS 7.8.4 on Ubuntu 20.04. The problem is also present 
when running r.param.scale from QGIS or rgrass7 (in a R session).

I have replicated the problem with another high resolution DEM of 
different source (still FCELL), and also with a 30 m SRTM DEM (CELL), 
but in this case the occurrence of these odd results is less frequent 
and they are not contrasting as much with the expected outcome ("only" 
by a 1 or 2 order of magnitude). The problem is present with or without 
the -c option, and seems only to affect the computation of curvatures 
(profc,planc,longc,crosc,minic,maxic).

Has anyone encountered something like that, or have any idea about what 
might be going on?

Thanks in advance,

Vincent

-- 
Vincent Godard
CEREGE, OSU Pythéas
Aix-Marseille Université
Europôle Méditerranéen de l’Arbois - BP 80
13545 Aix-en-Provence cedex 04, France
godard at cerege.fr