[GRASS-dev] r.watershed - too many negatives in the flow accum

Hi,

in nc dataset, running

g.region rast=elev_lid792_1m -p

r.watershed elevation=elev_lid792_1m
accumulation=elev_lid792_1m.acc
basin=elev_lid792_1m.basin
stream=elev_lid792_1m.stream
tci=elev_lid792_1m.tci
threshold=1000
-m

r.mapcalc “neg = if(elev_lid792_1m.acc < 0, 1, null())”

the map of negatives (problematic areas) presents the pattern shown in the attached screen shot. To me it looks weird, usually i find problematic areas on the border of the map, because the water basin is cut and a part of it falls outside the region. In this case they cover most of the area, the central part included. Any insight?

Thanks,
madi

Best regards,

Dr. Margherita DI LEO
Scientific / technical project officer

European Commission - DG JRC
Institute for Environment and Sustainability (IES)
Via Fermi, 2749
I-21027 Ispra (VA) - Italy - TP 261

Tel. +39 0332 78 3600
margherita.di-leo@jrc.ec.europa.eu

Disclaimer: The views expressed are purely those of the writer and may not in any circumstance be regarded as stating an official position of the European Commission.

(attachments)

Screenshot - 05282014 - 10:10:32 AM.png

On Wed, May 28, 2014 at 10:54 AM, Margherita Di Leo <
dileomargherita@gmail.com> wrote:

Hi,

in nc dataset, running

g.region rast=elev_lid792_1m -p

r.watershed elevation=elev_lid792_1m \
accumulation=elev_lid792_1m.acc \
basin=elev_lid792_1m.basin \
stream=elev_lid792_1m.stream \
tci=elev_lid792_1m.tci \
threshold=1000 \
-m

r.mapcalc "neg = if(elev_lid792_1m.acc < 0, 1, null())"

the map of negatives (problematic areas) presents the pattern shown in the
attached screen shot. To me it looks weird, usually i find problematic
areas on the border of the map, because the water basin is cut and a part
of it falls outside the region. In this case they cover most of the area,
the central part included. Any insight?

Here's the screen shot:

http://tinypic.com/view.php?pic=33b3fba&s=8#.U4WwNnV515E

grass is 7.0.0svn (r60523)

--
Best regards,

Dr. Margherita DI LEO
Scientific / technical project officer

European Commission - DG JRC
Institute for Environment and Sustainability (IES)
Via Fermi, 2749
I-21027 Ispra (VA) - Italy - TP 261

Tel. +39 0332 78 3600
margherita.di-leo@jrc.ec.europa.eu

Disclaimer: The views expressed are purely those of the writer and may not
in any circumstance be regarded as stating an official position of the
European Commission.