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
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--
Thomas E Adams
National Weather Service
Ohio River Forecast Center
1901 South State Route 134
Wilmington, OH 45177
EMAIL: [email protected]
VOICE: 937-383-0528
FAX: 937-383-0033
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