Hi Which module do I use to change the resolutions?
2010/7/6 <[email protected]> > Hello Sandile: > It seems you are importing two raster with vastly different resolutions. > (I think we already came across this). See below... > > > Hi > > > > Below is a step-by-step of what I have done but I'm getting an error when > > running v.rast.stats vector=catchments raster=rainfall layer=1 > > colprefix=area. > > > > > > GRASS 6.4.0RC5+39438 (SRTMDEM):~ > r.in.gdal > > in=/home/tgumede1/grassdata/Cape_Town/TRMMLast1day.tif out=rainfall > > > > Projection of input dataset and current location appear to match > > 100% > > r.in.gdal complete. Raster map <rainfall> created. > > GRASS 6.4.0RC5+39438 (SRTMDEM):~ > g.region rast=rainfall -p > > projection: 3 (Latitude-Longitude) > > zone: 0 > > datum: wgs84 > > ellipsoid: wgs84 > > north: 33:30S > > south: 33:45S > > west: 18:15E > > east: 19E > > nsres: 0:15 > > ewres: 0:15 > > rows: 1 > > cols: 3 > > cells: 3 > > Here, the rainfall data has a resolution of 0:15 = 15 minutes or 1/4 > degree. THat's approximately (at the equator) about 27 km. So *one* raster > cell is 27 km X 27 km =~ 730 sq.km. Your region is covered by 3 cells, 1 > row by 3 columns. Not very helpful data! > > Next... > > > GRASS 6.4.0RC5+39438 (SRTMDEM):~ > r.in.gdal > > in=/home/tgumede1/grassdata/Cape_Town/Dem_CF.tif out=dem target=SRTMDEM > > > > > > Projection of input dataset and current location appear to match > > 100% > > r.in.gdal complete. Raster map <dem> created. > > GRASS 6.4.0RC5+39438 (SRTMDEM):~ > g.region rast=dem -p > > projection: 3 (Latitude-Longitude) > > zone: 0 > > datum: wgs84 > > ellipsoid: wgs84 > > north: 33:40:46.499215S > > south: 34:00:52.499215S > > west: 18:17:55.500436E > > east: 19:10:16.500436E > > nsres: 0:00:03 > > ewres: 0:00:03 > > rows: 402 > > cols: 1047 > > cells: 420894 > > Your DEM layer, on the other hand, is of resolution 3 arc seconds, or > about 90 meters on a side. So each cell is 90 m. X 90 m = 8100 sq.m. =~ > 0.0081 sq.km. > > > GRASS 6.4.0RC5+39438 (SRTMDEM):~ > r.watershed elevation=dem > > accumulation=acc drainage=direction basin=catch stream=str threshold=200 > > > > Here you chose a threshold of 200. That's 200 cells, so about 200 X 0.0081 > sq.km, or 1.6 sq km. As a result (see below, the output of r.to.vect) you > are getting over 19,000 tiny little catchments. Are you sure that's what > you want?? > > Finally, you're trying to get raster values for 19,000 tiny vector areas > where the raster (rainfall) is only 3 cells! You'll have 1000's of > catchments with all the same values. And I guess that some of these > catchments are extending outside of the three rainfall cells, and causing > the NULL value error. > > In short: I think you'll need to match the resolution of the DEM to that > of the rainfall data. If the rainfall is only as accurate as 1 data value > per 730 sq.km. then you will be able to do vector-raster analyses only at > that resolution = i.e. continent scale maps. > > HTH > -- > Micha > > > > > SECTION 1a (of 5): Initiating Memory. > > SECTION 1b (of 5): Determining Offmap Flow. > > 100% > > SECTION 2: A * Search. > > 100% > > SECTION 3: Accumulating Surface Flow. > > 100% > > SECTION 4: Watershed determination. > > 100% > > SECTION 5: Closing Maps. > > 100% > > GRASS 6.4.0RC5+39438 (SRTMDEM):~ > r.to.vect -s in=catch out=catchments > > feature=area > > Extracting areas... > > 100% > > 100% > > Building topology for vector map <catchments>... > > Registering primitives... > > 60653 primitives registered > > 314051 vertices registered > > Building areas... > > 100% > > 19885 areas built > > 1 isles built > > Attaching islands... > > 100% > > Attaching centroids... > > 100% > > Number of nodes: 40769 > > Number of primitives: 60653 > > Number of points: 0 > > Number of lines: 0 > > Number of boundaries: 40768 > > Number of centroids: 19885 > > Number of areas: 19885 > > Number of isles: 1 > > r.to.vect complete. > > > > GRASS 6.4.0RC5+39438 (SRTMDEM):~ > v.rast.stats vector=catchments > > raster=rainfall layer=1 colprefix=precip > > > > DBMI-DBF driver error: > > SQL parser error: syntax error, unexpected NULL_VALUE processing 'NULL' > > in statement: > > UPDATE catchments SET precip_min=-NULL WHERE cat=10163 > > Error in db_execute_immediate() > > > > ERROR: Error while executing: 'UPDATE catchments SET precip_min=-NULL > > WHERE > > cat=10163' > > > > > > > > Here is the output of gdalinfo TRMMLast1day.tif > > > > Origin = (18.250000000000000,-33.500000000000000) > > Pixel Size = (0.250000000000000,-0.250000000000000) > > > > -------------------- > > coordinates-------------------------------------------- > > Corner Coordinates: > > Upper Left ( 18.2500000, -33.5000000) > > Lower Left ( 18.2500000, -33.7500000) > > Upper Right ( 19.0000000, -33.5000000) > > Lower Right ( 19.0000000, -33.7500000) > > Center ( 18.6250000, -33.6250000) > > > > > > Here is what I did to clip the region of interest. > > > > gdal_translate -a_srs EPSG:4326 -projwin 18.2987501 -33.6795831 > 19.1712501 > > -34.0141665 3B42RT.2010032900.1day.tif TRMMLast1day.tif > > > > > > Is there something I have done wrong in these steps or there is something > > wrong with my coordinates? > > > > > > > > 2010/7/6 <[email protected]> > > > >> > Hi > >> > > >> > Is it wrong to use -a_ullr option in gdal_translate to clip a small > >> > portion > >> > of the region from the big geotiff file region? > >> > > >> > >> The option -a_ullr will change the georeference of the resulting file, > >> so > >> you could say it's "wrong" if you want to keep the original referencing. > >> The way to clip a portion of the original and still maintain > >> geo-referencing is with the -projwin option. > >> > >> -- > >> Micha > >> > >> > -- > >> > Kind Regards > >> > TS Gumede > >> > CSIR, Meraka Institute > >> > 072 258 1650 > >> > > >> > This mail was received via Mail-SeCure System. > >> > > >> > > >> > > >> > >> > > > > > > -- > > Kind Regards > > TS Gumede > > CSIR, Meraka Institute > > 072 258 1650 > > > > This mail was received via Mail-SeCure System. > > > > > > > > -- Kind Regards TS Gumede CSIR, Meraka Institute 072 258 1650
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