[GRASS-user] faster than v.rast.stats

[Thomas Adams]

  Frederico,

One possible way is to generate a raster MASK file from the vector data 
and, using the mask for each polygonal area and R, calculate statistics 
that way. Although, honestly, I don't know if that would be faster or not.

Another possibility is something like this (snippit from a GRASS script 
in a Linux environment), that we have used where speed is critical:


#
# remove previous vector file and create new from precip file, where 
$DTYPE and $INFILE are script inputs;
# so, if you are reading rasters rater than point data, some coding can 
be eliminated
#
g.remove vect=ens$DTYPE,basevect$DTYPE
v.in.ascii input=$INFILE output=ens$DTYPE format=point x=3 y=2 z=4 cat=0

# create raster from vector points and display
g.remove rast=ensrast$DTYPE,basemap,ensint$DTYPE,ensavg$DTYPE

# Adjusting the number of points for weight calculations
v.surf.idw -n input=ens$DTYPE output=ensrast$DTYPE npoints=4 col=dbl_3
g.copy vect=$BASINVECT,basevect$DTYPE
echo "Before r.mapcalc"
r.mapcalc "ensint$DTYPE=round(100*ensrast$DTYPE)"
echo "After r.mapcalc"
v.build map=basevect$DTYPE
r.statistics base=$BASINVECT cover=ensint$DTYPE method=average 
output=ensavg$DTYPE
r.cats map=ensavg$DTYPE > ensgrass.$DTYPE.out

then outside the script above:

      ensgrass.ksh PCP latlong.out
      fname=qpf.$dd.$ff.$mx$mnum
      join basins.out ensgrass.$DTYPE.out > output/$fname

where ensgrass.ksh is the calling script the the GRASS snippit above. 
'PCP' is a keyword and 'latlong.out' is the input file to ensgrass.ksh. 
The end result, following the join, is that you get average values for 
the polygon areas associated by the polygon IDs in basins.out

basins.out is a text file that looks like this:

1    WENM1
2    DOVM1
3    WYMM1
4    EBKV1
5    EDDM1
6    ROUN6
7    NSTN3
8    NANM1
9    PITM1
10    SIDM1
11    SKOM1
12    MERM1
13    CZRN6
14    NTYV1
15    SWAV1
16    GEOV1
17    RMFM1
18    JONV1
19    ESSV1
20    AUSN6



Tom

On 6/21/11 10:03 AM, Frederico Mestre wrote:
>
> Hello,
>
> I'm trying to retrieve some statistics from several rasters, based on 
> overlaying vectors.
>
> I'm using v.rast.stats but it is very slow. Is there another way?
>
> I read something about Starspan, a software that does this same thing 
> faster, but I can,t find it to download.
>
> Can anybody help?
>
> Frederico Mestre
>
>
> _______________________________________________
> grass-user mailing list
> grass-user at lists.osgeo.org
> http://lists.osgeo.org/mailman/listinfo/grass-user


-- 
Thomas E Adams
National Weather Service
Ohio River Forecast Center
1901 South State Route 134
Wilmington, OH 45177

EMAIL:	thomas.adams at noaa.gov

VOICE:	937-383-0528
FAX:	937-383-0033

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