[GRASS-user] Problem with r.basin in grass7

[Helmut Kudrnovsky]

> I still have a problem, since my DEMs have a very high resolution.  I tried
to run r.basin using a lower resolution of the DEMs, but I do get an error. 

any reason why not use the original DEM resolution?

AFAIK as the underlying modules (r.watershed, r.stream.*) are sensitive to
region and resolution settings (please see their manuals regarding this).
resolution resampling may introduce some artefacts which may be some issues
for these modules.

>B) Run r.basin using a lower resolution DEM
>B1) I changed the resolution of the computational region
> 
>.region res=35 <=
> 
>g.region -p                                                                    
>projection: 99 (Lambert Conformal Conic)
>zone:       0
>datum:      nad83
>ellipsoid:  a=6378137 es=0.006694380022900787
>north:      228500
>south:      215000
>west:       630000
>east:       645000
>nsres:      34.97409326  <=
>ewres:      34.96503497  <=
>rows:       386
>cols:       429
>cells:      165594 

see: 35 vs 34.97409326

you have to align the region to the resolution:

g.region -p -a raster=elev_ned_30m at PERMANENT align=elev_ned_30m at PERMANENT       
projection: 99 (Lambert Conformal Conic)
zone:       0
datum:      nad83
ellipsoid:  a=6378137 es=0.006694380022900787
north:      228500
south:      215000
west:       630000
east:       645000
nsres:      30
ewres:      30
rows:       450
cols:       500
cells:      225000
(Wed Dec 17 09:13:43 2014) Befehl ausgeführt (0 Sek)  
                          
(Wed Dec 17 09:14:06 2014)                                                      
g.region -p -a res=35                                                           
projection: 99 (Lambert Conformal Conic)
zone:       0
datum:      nad83
ellipsoid:  a=6378137 es=0.006694380022900787
north:      228515
south:      214970
west:       630000
east:       645015
nsres:      35
ewres:      35
rows:       387
cols:       429
cells:      166023
(Wed Dec 17 09:14:07 2014) Befehl ausgeführt (0 Sek)                            




-----
best regards
Helmut
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