On 07/22/2010 10:55 AM, Sandile Gumede wrote:
Hi
How do you remove null cells, I guess that is what's causing the problem.
Sandile:
If I remember your project details, I think that the problem is not the
null cells in your rainfall data, but rather the very small catchment
polygons, some of which fall *totally* within a single rainfall cell
which has a null value.
r.to.vect complete.
I guess this step is your conversion of basins to a polygon vector map?
How many polygons are you getting? Check with v.info. What size are they?
v.db.addcol catchments col="area_sqm double precision"
v.to.db catchments opt=area col=area_sqm units=me
And please remind us of the resolution of the rainfall raster with:
r.info rainfall
GRASS 6.4.0svn (SRTMDEM):~ > r.univar rainfall 100%
total null and non-null cells: 12967201
total null cells: 7202
Of the non-null cells:
----------------------
n: 12959999
minimum: 0
maximum: 36
range: 36
mean: 4.99965
mean of absolute values: 4.99965
standard deviation: 9.57207
variance: 91.6246
variation coefficient: 191.455 %
sum: 64795464
GRASS 6.4.0svn (SRTMDEM):~ > v.rast.stats vect=catchments
rast=rainfall colprefix=precip
Processing data (16 categories)...
Updating the database ...
DBMI-DBF driver error:
SQL parser error: syntax error processing 'NULL'
in statement:
UPDATE catchments SET precip_cf_=-NULL WHERE cat=10728
Error in db_execute_immediate()
ERROR: Error while executing: 'UPDATE catchments SET precip_cf_=-NULL
WHERE
cat=10728'
Another suggestion: One of the catchment polygons that is failing above
has cat value 10728. How about extracting just that single polygon, then
display it on a map together with the rainfall raster to see where it
falls?
# extract
v.extract catchments out=catch_10728 where="cat=10728"
# Display
g.region rast=rainfall
d.rast rainfall
d.vect catch_10728
--
cheers,
Micha
--
Kind Regards
TS Gumede
CSIR, Meraka Institute
072 258 1650
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--
Micha Silver
Arava Development Co. +972-52-3665918
http://surfaces.co.il
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