[GRASS-user] how to calculate area of voronoi polygons considering the boundary of the catchment
Hi, I have the point rainfall data of a region. Few of the point data are outside the region of interest. I am making the voronoi polygons using the v.voronoi on the vector imported from this point ascii (x,y,z) data. The polygon may be fully inside the region of interest or may be partially outside the region of interest. In case of the polygon which is partially outside the region of interest, the area which is inside the region of interest need to be calculated. How to calculate this? How can i calculate the area of voronoi polygon. Thanks in advance. Daljeet -- View this message in context: http://n2.nabble.com/how-to-calculate-area-of-voronoi-polygons-considering-the-boundary-of-the-catchment-tp3335923p3335923.html Sent from the Grass - Users mailing list archive at Nabble.com. ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] how to calculate area of voronoi polygons considering the boundary of the catchment
On 27/07/09 21:38, daljeet wrote: Hi, I have the point rainfall data of a region. Few of the point data are outside the region of interest. I am making the voronoi polygons using the v.voronoi on the vector imported from this point ascii (x,y,z) data. The polygon may be fully inside the region of interest or may be partially outside the region of interest. In case of the polygon which is partially outside the region of interest, the area which is inside the region of interest need to be calculated. How to calculate this? - Define region of interest with g.region. - Create polygon of region with v.in.region. - Overlay voronoi polygons with region polygon with v.overlay operator=AND How can i calculate the area of voronoi polygon. v.report or v.to.db Moritz ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] how to calculate area of voronoi polygons considering the boundary of the catchment
Thanks Moritz. I was wrongly using the term "region" in my question above. The requirement is slightly different. Let me explain you in detail. Inputs: 1. I have got the shapefile data of the country. I imported it using v.in.ogr and extracted (v.extract) the vector of the desired "State" using the "where" clause on the attribute which contains the name of the States. So, this means i have the vector of a particular State and its area is available using v.report. 2. I have also got the rainfall point data for the entire country in the ascii file (x,y,z) for one week (z being the amount of rainfall) Output required: The volume of rainfall in the particular State (which is extracted above). What I am doing: I wanted to apply both, the Thiessen polygon and the Isohyetal Method to calculate the volume of rainfall. Till now I am only working on Thiessen, and this is what i have done: 1. Imported the ascii rainfall point data (v.in.ascii) in the vector. This is the vector for the whole country. 2. Created the voronoi vector on the above rainfall vector (v.voronoi) 3. Overlaid the voronoi rainfall vector of the country (from step 2) on the extracted vector of the State (from input 1 above) with AND operator. To verify, the sum of "area of each polygon" on the overlaid vector should be same as area of the extracted State vector. But this is not coming out to be same. The area of the voronoi overlaid map is smaller than the area of the extracted shape of State. One observation, the voronoi overlaid map shows some white grids (both inside and at the boundary of the map) and I suspect if these are being taken into account for the area. Attached is the png image of the overlaid vectors. http://n2.nabble.com/file/n3342895/rainfall_theissen_png.png Any idea what could be my mistake. What I am doing which is making the loss of area in the case of polygons. Thanks daljeet Moritz Lennert wrote: > > On 27/07/09 21:38, daljeet wrote: >> Hi, >> >> I have the point rainfall data of a region. Few of the point data are >> outside the region of interest. >> >> I am making the voronoi polygons using the v.voronoi on the vector >> imported >> from this point ascii (x,y,z) data. >> >> The polygon may be fully inside the region of interest or may be >> partially >> outside the region of interest. >> >> In case of the polygon which is partially outside the region of interest, >> the area which is inside the region of interest need to be calculated. >> How >> to calculate this? > > - Define region of interest with g.region. > - Create polygon of region with v.in.region. > - Overlay voronoi polygons with region polygon with v.overlay operator=AND > >> How can i calculate the area of voronoi polygon. > > v.report or v.to.db > > Moritz > ___ > grass-user mailing list > grass-user@lists.osgeo.org > http://lists.osgeo.org/mailman/listinfo/grass-user > > -- View this message in context: http://n2.nabble.com/how-to-calculate-area-of-voronoi-polygons-considering-the-boundary-of-the-catchment-tp3335923p3342895.html Sent from the Grass - Users mailing list archive at Nabble.com. ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] how to calculate area of voronoi polygons considering the boundary of the catchment
On 28/07/09 16:02, daljeet wrote: Thanks Moritz. I was wrongly using the term "region" in my question above. The requirement is slightly different. Let me explain you in detail. Inputs: 1. I have got the shapefile data of the country. I imported it using v.in.ogr and extracted (v.extract) the vector of the desired "State" using the "where" clause on the attribute which contains the name of the States. So, this means i have the vector of a particular State and its area is available using v.report. 2. I have also got the rainfall point data for the entire country in the ascii file (x,y,z) for one week (z being the amount of rainfall) Output required: The volume of rainfall in the particular State (which is extracted above). What I am doing: I wanted to apply both, the Thiessen polygon and the Isohyetal Method to calculate the volume of rainfall. Till now I am only working on Thiessen, and this is what i have done: 1. Imported the ascii rainfall point data (v.in.ascii) in the vector. This is the vector for the whole country. 2. Created the voronoi vector on the above rainfall vector (v.voronoi) 3. Overlaid the voronoi rainfall vector of the country (from step 2) on the extracted vector of the State (from input 1 above) with AND operator. To verify, the sum of "area of each polygon" on the overlaid vector should be same as area of the extracted State vector. But this is not coming out to be same. The area of the voronoi overlaid map is smaller than the area of the extracted shape of State. One observation, the voronoi overlaid map shows some white grids (both inside and at the boundary of the map) and I suspect if these are being taken into account for the area. Attached is the png image of the overlaid vectors. http://n2.nabble.com/file/n3342895/rainfall_theissen_png.png Any idea what could be my mistake. What I am doing which is making the loss of area in the case of polygons. Sorry, cannot help you as such. Start by giving the exact command lines used with each command. Also show the results of v.voronoi. And how did you calculate the areas ? Moritz ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] how to calculate area of voronoi polygons considering the boundary of the catchment
Hi Moritz, I am new to GRASS and the basic concepts of this field. Below, I tried my best to share all the information. Please write if I have missed anything. List of commands issued in sequence: //import of shapefile data of country v.in.ogr -e dsn="IND_adm2.shp" output="Ind_adm2_v" min_area=0.0001 snap=-1 //extract the desired State (in my case it is the state of Kerala) v.extract input=Ind_adm2_v output=Ind_adm2_ker new=1 where="(Name_1 = 'Kerala')" //set to region to the vector created for the State g.region vect=Ind_adm2_ker //displays as d.vect Ind_adm2_ker http://n2.nabble.com/file/n3344342/Ind_adm2_ker.png //area of Kerala state v.report Ind_adm2_ker option=area units=k cat|area 1|37700.7050169835 //import of rainfall data of the country for a week (available in ascii format) v.in.ascii input="/home/daljeet/grassdata/India_Data_From_DST/india_rain_orig.txt" output="Ind_rain_orig" format="point" fs="\t" skip=1 columns="x double precision, y double precision, rain_info double precision" x=2 y=1 z=0 cat=0 //creating the voronoi v.voronoi input="Ind_rain_orig" output="Ind_rain_ker_vor" //display the voronoi d.vect "Ind_rain_ker_vor" http://n2.nabble.com/file/n3344342/Ind_rain_ker_vor.png //overlay v.overlay ainput="Ind_adm2_ker" atype="area" alayer=1 binput="Ind_rain_ker_vor" btype="area" blayer=1 output="ker_rain_vor_over" operator="and" olayer=1,0,0 //show the overlaid vector d.vect ker_rain_vor_over http://n2.nabble.com/file/n3344342/ker_rain_vor_over.png //storing the area of each polygon to a csv file v.report ker_rain_vor_over option=area units=k >ker_area.csv --o attached is the csv file ker_area.csv http://n2.nabble.com/file/n3344342/ker_area.csv ker_area.csv Sum of the area of polygon in the last column is 23881.22 (which is not equal to the one which is calculated above for Kerala Stata, 37700.7050169835) Thanks Daljeet Moritz Lennert wrote: > > On 28/07/09 16:02, daljeet wrote: >> Thanks Moritz. >> >> I was wrongly using the term "region" in my question above. The >> requirement >> is slightly different. Let me explain you in detail. >> >> Inputs: >> 1. I have got the shapefile data of the country. I imported it using >> v.in.ogr and extracted (v.extract) the vector of the desired "State" >> using >> the "where" clause on the attribute which contains the name of the >> States. >> So, this means i have the vector of a particular State and its area is >> available using v.report. >> >> 2. I have also got the rainfall point data for the entire country in the >> ascii file (x,y,z) for one week (z being the amount of rainfall) >> >> Output required: >> The volume of rainfall in the particular State (which is extracted >> above). >> >> What I am doing: >> I wanted to apply both, the Thiessen polygon and the Isohyetal Method to >> calculate the volume of rainfall. >> >> Till now I am only working on Thiessen, and this is what i have done: >> 1. Imported the ascii rainfall point data (v.in.ascii) in the vector. >> This >> is the vector for the whole country. >> 2. Created the voronoi vector on the above rainfall vector (v.voronoi) >> 3. Overlaid the voronoi rainfall vector of the country (from step 2) on >> the >> extracted vector of the State (from input 1 above) with AND operator. >> >> To verify, the sum of "area of each polygon" on the overlaid vector >> should >> be same as area of the extracted State vector. >> >> But this is not coming out to be same. The area of the voronoi overlaid >> map >> is smaller than the area of the extracted shape of State. One >> observation, >> the voronoi overlaid map shows some white grids (both inside and at the >> boundary of the map) and I suspect if these are being taken into account >> for >> the area. Attached is the png image of the overlaid vectors. >> >> http://n2.nabble.com/file/n3342895/rainfall_theissen_png.png >> >> Any idea what could be my mistake. What I am doing which is making the >> loss >> of area in the case of polygons. > > Sorry, cannot help you as such. Start by giving the exact command lines > used with each command. Also show the results of v.voronoi. And how did > you calculate the areas ? > > Moritz > ___ > grass-user mailing list > grass-user@lists.osgeo.org > http://lists.osgeo.org/mailman/listinfo/grass-user > > -- View this message in context: http://n2.nabble.com/how-to-calculate-area-of-voronoi-polygons-considering-the-boundary-of-the-catchment-tp3335923p3344342.html Sent from the Grass - Users mailing list archive at Nabble.com. ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] how to calculate area of voronoi polygons considering the boundary of the catchment
On 28/07/09 18:42, daljeet wrote: Hi Moritz, I am new to GRASS and the basic concepts of this field. Below, I tried my best to share all the information. Please write if I have missed anything. This is perfect, thanks ! //creating the voronoi v.voronoi input="Ind_rain_orig" output="Ind_rain_ker_vor" //display the voronoi d.vect "Ind_rain_ker_vor" http://n2.nabble.com/file/n3344342/Ind_rain_ker_vor.png The problem is here, with v.voronoi, as you can see the white spots here. What do the original points (Ind_rain_orig) look like ? I don't know the module well enough, but I think you might have hit a bug there (I've just tried a simple example for myself and also get weird white spots). Please file a report in the bug tracker. //storing the area of each polygon to a csv file v.report ker_rain_vor_over option=area units=k >ker_area.csv --o Note that you can use v.addcol and v.to.db upload the polygon areas to the attribute table. Moritz ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] how to calculate area of voronoi polygons considering the boundary of the catchment
These white spots in the voronoi vector may be the cause. But i ran the voronoi module on the "archsites" vector of the Spearfish60 dataset and its runs fine. The cmd was v.voronoi input="archsites" output="arch_voronoi" The only difference is that the region of archsites has got less points (around 25) whereas in Ind_rain_orig the total points were 93,000. Can this be an issue. Can you test the module at your end with less and huge data points and see if you also get similar results in both the cases. This would be a great help. Also, i checked and the data of rain fall on voronoi vector is NOT NULL on these white spots (checked using v.what.vect). //d.vect Ind_rain_orig //The Ind_rain_orig looks like this - when the region is set to vector of Kerala //g.region vect=ker_rain_v http://n2.nabble.com/file/n3345107/Ind_rain_orig_reg_ker.png But when the region is set to Ind_adm2_v (whole country) the image is like //g.region vect=Ind_adm2_v //d.vect Ind_rain_orig http://n2.nabble.com/file/n3345107/Ind_rain_orig_reg_adm2.png Thanks Daljeet Moritz Lennert wrote: > > On 28/07/09 18:42, daljeet wrote: >> Hi Moritz, >> >> I am new to GRASS and the basic concepts of this field. Below, I tried my >> best to share all the information. Please write if I have missed >> anything. > > This is perfect, thanks ! > >> //creating the voronoi >> v.voronoi input="Ind_rain_orig" output="Ind_rain_ker_vor" >> >> //display the voronoi >> d.vect "Ind_rain_ker_vor" >> >> http://n2.nabble.com/file/n3344342/Ind_rain_ker_vor.png >> > > The problem is here, with v.voronoi, as you can see the white spots > here. What do the original points (Ind_rain_orig) look like ? > > I don't know the module well enough, but I think you might have hit a > bug there (I've just tried a simple example for myself and also get > weird white spots). Please file a report in the bug tracker. > > >> >> //storing the area of each polygon to a csv file >> v.report ker_rain_vor_over option=area units=k >ker_area.csv --o > > Note that you can use v.addcol and v.to.db upload the polygon areas to > the attribute table. > > Moritz > ___ > grass-user mailing list > grass-user@lists.osgeo.org > http://lists.osgeo.org/mailman/listinfo/grass-user > > -- View this message in context: http://n2.nabble.com/how-to-calculate-area-of-voronoi-polygons-considering-the-boundary-of-the-catchment-tp3335923p3345107.html Sent from the Grass - Users mailing list archive at Nabble.com. ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] how to calculate area of voronoi polygons considering the boundary of the catchment
http://www.intevation.de/rt/webrt?serial_num=4292&display=History The problem that we are facing may be related to above issue. Thanks Daljeet daljeet wrote: > > These white spots in the voronoi vector may be the cause. But i ran the > voronoi module on the "archsites" vector of the Spearfish60 dataset and > its runs fine. The cmd was > > v.voronoi input="archsites" output="arch_voronoi" > > The only difference is that the region of archsites has got less points > (around 25) whereas in Ind_rain_orig the total points were 93,000. Can > this be an issue. Can you test the module at your end with less and huge > data points and see if you also get similar results in both the cases. > This would be a great help. > > Also, i checked and the data of rain fall on voronoi vector is NOT NULL on > these white spots (checked using v.what.vect). > > //d.vect Ind_rain_orig > //The Ind_rain_orig looks like this - when the region is set to vector of > Kerala > //g.region vect=ker_rain_v > > http://n2.nabble.com/file/n3345107/Ind_rain_orig_reg_ker.png > > But when the region is set to Ind_adm2_v (whole country) the image is > like > //g.region vect=Ind_adm2_v > //d.vect Ind_rain_orig > > http://n2.nabble.com/file/n3345107/Ind_rain_orig_reg_adm2.png > > Thanks > Daljeet > > Moritz Lennert wrote: >> >> On 28/07/09 18:42, daljeet wrote: >>> Hi Moritz, >>> >>> I am new to GRASS and the basic concepts of this field. Below, I tried >>> my >>> best to share all the information. Please write if I have missed >>> anything. >> >> This is perfect, thanks ! >> >>> //creating the voronoi >>> v.voronoi input="Ind_rain_orig" output="Ind_rain_ker_vor" >>> >>> //display the voronoi >>> d.vect "Ind_rain_ker_vor" >>> >>> http://n2.nabble.com/file/n3344342/Ind_rain_ker_vor.png >>> >> >> The problem is here, with v.voronoi, as you can see the white spots >> here. What do the original points (Ind_rain_orig) look like ? >> >> I don't know the module well enough, but I think you might have hit a >> bug there (I've just tried a simple example for myself and also get >> weird white spots). Please file a report in the bug tracker. >> >> >>> >>> //storing the area of each polygon to a csv file >>> v.report ker_rain_vor_over option=area units=k >ker_area.csv --o >> >> Note that you can use v.addcol and v.to.db upload the polygon areas to >> the attribute table. >> >> Moritz >> ___ >> grass-user mailing list >> grass-user@lists.osgeo.org >> http://lists.osgeo.org/mailman/listinfo/grass-user >> >> > > -- View this message in context: http://n2.nabble.com/how-to-calculate-area-of-voronoi-polygons-considering-the-boundary-of-the-catchment-tp3335923p3345998.html Sent from the Grass - Users mailing list archive at Nabble.com. ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] how to calculate area of voronoi polygons considering the boundary of the catchment
On Tue, 28 Jul 2009 11:24:19 -0700 (PDT) daljeet wrote: > > > > //d.vect Ind_rain_orig > //The Ind_rain_orig looks like this - when the region is set to > vector of Kerala > //g.region vect=ker_rain_v > > http://n2.nabble.com/file/n3345107/Ind_rain_orig_reg_ker.png > > But when the region is set to Ind_adm2_v (whole country) the image > is like //g.region vect=Ind_adm2_v > //d.vect Ind_rain_orig > > http://n2.nabble.com/file/n3345107/Ind_rain_orig_reg_adm2.png > Since you seem to have a rigid matrix of data points, what's the purpose of the voronoi polygons?? Can't you just run v.surf.rst to get a rain_info raster surface, then r.contour to make your isohyetal lines? Finallly v.rast.stats will add columns to the vector table with all the rainfall statistics. > Thanks > Daljeet > > Moritz Lennert wrote: > > > > On 28/07/09 18:42, daljeet wrote: > >> Hi Moritz, > >> > >> I am new to GRASS and the basic concepts of this field. Below, I > >> tried my best to share all the information. Please write if I have > >> missed anything. > > > > This is perfect, thanks ! > > > >> //creating the voronoi > >> v.voronoi input="Ind_rain_orig" output="Ind_rain_ker_vor" > >> > >> //display the voronoi > >> d.vect "Ind_rain_ker_vor" > >> > >> http://n2.nabble.com/file/n3344342/Ind_rain_ker_vor.png > >> > > > > The problem is here, with v.voronoi, as you can see the white spots > > here. What do the original points (Ind_rain_orig) look like ? > > > > I don't know the module well enough, but I think you might have hit > > a bug there (I've just tried a simple example for myself and also > > get weird white spots). Please file a report in the bug tracker. > > > > > >> > >> //storing the area of each polygon to a csv file > >> v.report ker_rain_vor_over option=area units=k >ker_area.csv --o > > > > Note that you can use v.addcol and v.to.db upload the polygon areas > > to the attribute table. > > > > Moritz > > ___ > > grass-user mailing list > > grass-user@lists.osgeo.org > > http://lists.osgeo.org/mailman/listinfo/grass-user > > > > > ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] how to calculate area of voronoi polygons considering the boundary of the catchment
Hi Micha, I could create isohyetal lines using the suggested steps: -v.in.ascii v.in.ascii x=2 y=1 cat=0 input="01_08nov2001" out="rainvector" columns="x double precision, y double precision, rain_info double precision" --o fs="\t" skip=1 - set the region to smaller vector and set the mask created from the same smaller region vector- this is to reduce the computation and work on smaller region. -v.surf.rst (without playing around with tension and smooothness) v.surf.rst rainvector zcol=rain_info elev=rainraster --o -r.contour r.contour step=10 input=rainraster output=rainvector_con -v.rast.stats v.rast.stats rainvector_con raster=rainraster colprefix=pre The generated image is like this http://n2.nabble.com/file/n3555804/rainvector_con.png Following are the doubts/questions 1. I saw the details of the raster created from v.surf.rst >r.info rainraster zmin_data=0.00, zmax_data=141.322000| zmin_int=-13.588332, zmax_int=52.589905 zmin_data and zmax_data seems to be correct but I do not understand a) why the interpolated value zmin_int=-13.588332 is -ve b) and what is meaning of zmax_int equal to 52.589905 2. The target is to be able to calculate the area between two isohyetal lines and multiplying that area with the average rainfall within the two isohyets. This is to be done for all isohyetal lines. Average can be calculated by averaging the value of rainfall of the two isohyetal lines. But how to calculate the area b/w the two isohyetal lines? >v.db.select rainvector_con cat|level|pre_n|pre_min|pre_max|pre_range|pre_mean|pre_stddev|pre_varian|pre_cf_var|pre_sum 1|0|722|-7.148755|1.627629|8.776384|-0.028756|0.424996|0.180621|-1477.946779|-20.761703 2|10|820|0.515458|13.074255|12.558797|10.01766|0.67391|0.454155|6.727224|8214.481322 3|20|557|10.988949|23.001575|12.012627|19.92515|0.938034|0.879908|4.707789|11098.308486 4|30|341|19.780724|33.184017|13.403294|29.949896|1.289828|1.663655|4.306618|10212.914476 5|40|168|31.07769|42.131256|11.053566|39.848495|1.331978|1.774164|3.342605|6694.547157 6|50|13|44.652187|52.589905|7.937717|49.761042|1.654373|2.73695|3.324635|646.893547 Thanks Daljeet Micha Silver wrote: > > On Tue, 28 Jul 2009 11:24:19 -0700 (PDT) > daljeet wrote: > >> >> >> >> //d.vect Ind_rain_orig >> //The Ind_rain_orig looks like this - when the region is set to >> vector of Kerala >> //g.region vect=ker_rain_v >> >> http://n2.nabble.com/file/n3345107/Ind_rain_orig_reg_ker.png >> >> But when the region is set to Ind_adm2_v (whole country) the image >> is like //g.region vect=Ind_adm2_v >> //d.vect Ind_rain_orig >> >> http://n2.nabble.com/file/n3345107/Ind_rain_orig_reg_adm2.png >> > > Since you seem to have a rigid matrix of data points, what's the > purpose of the voronoi polygons?? > Can't you just run v.surf.rst to get a rain_info raster surface, then > r.contour to make your isohyetal lines? Finallly v.rast.stats will add > columns to the vector table with all the rainfall statistics. > > > >> Thanks >> Daljeet >> >> Moritz Lennert wrote: >> > >> > On 28/07/09 18:42, daljeet wrote: >> >> Hi Moritz, >> >> >> >> I am new to GRASS and the basic concepts of this field. Below, I >> >> tried my best to share all the information. Please write if I have >> >> missed anything. >> > >> > This is perfect, thanks ! >> > >> >> //creating the voronoi >> >> v.voronoi input="Ind_rain_orig" output="Ind_rain_ker_vor" >> >> >> >> //display the voronoi >> >> d.vect "Ind_rain_ker_vor" >> >> >> >> http://n2.nabble.com/file/n3344342/Ind_rain_ker_vor.png >> >> >> > >> > The problem is here, with v.voronoi, as you can see the white spots >> > here. What do the original points (Ind_rain_orig) look like ? >> > >> > I don't know the module well enough, but I think you might have hit >> > a bug there (I've just tried a simple example for myself and also >> > get weird white spots). Please file a report in the bug tracker. >> > >> > >> >> >> >> //storing the area of each polygon to a csv file >> >> v.report ker_rain_vor_over option=area units=k >ker_area.csv --o >> > >> > Note that you can use v.addcol and v.to.db upload the polygon areas >> > to the attribute table. >> > >> > Moritz >> > ___ >> > grass-user mailing list >> > grass-user@lists.osgeo.org >> > http://lists.osgeo.org/mailman/listinfo/grass-user >> > >> > >> > ___ > grass-user mailing list > grass-user@lists.osgeo.org > http://lists.osgeo.org/mailman/listinfo/grass-user > > -- View this message in context: http://n2.nabble.com/how-to-calculate-area-of-voronoi-polygons-considering-the-boundary-of-the-catchment-tp3335923p3555804.html Sent from the Grass - Users mailing list archive at Nabble.com. ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] how to calculate area of voronoi polygons considering the boundary of the catchment
Hi Daljeet daljeet wrote: Hi Micha, I could create isohyetal lines using the suggested steps: ... clipped... Following are the doubts/questions 1. I saw the details of the raster created from v.surf.rst r.info rainraster zmin_data=0.00, zmax_data=141.322000| zmin_int=-13.588332, zmax_int=52.589905 zmin_data and zmax_data seems to be correct but I do not understand a) why the interpolated value zmin_int=-13.588332 is -ve b) and what is meaning of zmax_int equal to 52.58990 If I understand correctly, the zmax_int and zmin_int are the max and min displacements of the interpolated values vs. the actual data points. The RST method creates an interpolation which does not usually go thru the actual data points, but rather "smooths" over them. These numbers show the drift above and below actual data points. So you have one point where the interpolated rainfall is 13 mm (or whatever the rain units are) below the actual data, and one point where the interpolation is 52 mm above. 2. The target is to be able to calculate the area between two isohyetal lines and multiplying that area with the average rainfall within the two isohyets. This is to be done for all isohyetal lines. Average can be calculated by averaging the value of rainfall of the two isohyetal lines. But how to calculate the area b/w the two isohyetal lines? Well I can think of two approaches to this. 1- Using vectors: You might try to convert the isolines to closed boundaries, then add centroids and find some way to get the rainfall values into the centroids. This would require first to create an "edge" line all around the region (v.in.region will do this) to close the ends of the isolines, then run v.clean with the "break" tool to get nodes where each contour line crosses this region line. Then you should be able to convert the lines to closed boundaries (v.type) and finally v.centroids to create centroids in each of the resulting strips between isohyetal lines. But this procedure looks way to convoluted to me. Instead maybe you could try: 2- Using rasters: You already have the rainfall raster. Perhaps create a reclass raster map of the rainfall raster using discrete values instead of the continuous range. So your reclass rules would look something like: 0 thru 20 = 10 21 thru 40 = 30 41 thru 60 = 50 ... This will group together all values in the interval between 0-20 and give them the value midway between, etc. Then you could do r.to.vect fea=area to create a vector map, and finally v.db.addtable and v.to.db to get the areas of each strip into the vector attribute table. (Note that r.reclass requires an integer raster) After that long-winded response, I should add one more comment: Rainfall is not a continuous phenomena across a geographic area. There's no reason to expect that between the 40 mm line and the 60 mm line the average rainfall is 50 mm. If you stay with the original, continuous rainfall raster, and use v.rast.stats then the statistics are totalled on a cell by cell basis, and you avoid the "unnatural" results that might pop up when forcing the data into a framework of arbitrary intervals. Regards, Micha ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] how to calculate area of voronoi polygons considering the boundary of the catchment
Thanks. I am using the first method that you suggested. But it fails to create centroids whereas there are multiple isohyetal strips now and each should have been given the centroid. To give you the details on what i did. In real scenario, we will have the defined catchment area (which will be a close polygon shaped vector) with rainfall measurements on various gauge points (some gauge points will be within the catchment boundary and some will be outside that catchment area, but within the region of the catchment vector). Please correct me if I am wrong. I am simulating the above scenario by a) making a xyz point data file. x,y being lat and long and z being the measurement of rainfall. b) catchment is represented by a vector (basin_v) > g.region vect=basin_v #import the xyz pt data > v.in.ascii x=2 y=1 cat=0 input="rain_data" out="rainpoint_v" columns="x > double precision, y double precision, rain_info double precision" fs="\t" > skip=1 --o >MASK applied (which represents the raster of the catchment area with each cell value equal to 1) >v.surf.rst rainpoint_v zcol=rain_info elev=rain_rst --o >r.contour step=1 input=rain_rst output=rain_con_v At this stage, i have two seperate vectors, a) contour vector (rain_con_v) which has the lines only b) vector representing the catchment area (basin_v) whose topo details are as follows >v.info rain_con_v -t nodes=7 points=0 lines=7 boundaries=0 centroids=0 areas=0 islands=0 faces=0 kernels=0 primitives=7 map3d=1 Please note the below output. This may be reason of failure. >v.info basin_v -t nodes=2 points=0 lines=0 boundaries=1 centroids=1 areas=1 islands=1 faces=0 kernels=0 primitives=2 map3d=0 Now, as you suggested, i need to apply the v.clean (with break) to create the nodes at the intersection of isolines and boundary of the catchment vector. And for the input of v.clean, I patched the above two vectors using v.patch. Please correct if this is the right step or something else would have been done? > v.patch input=rain_con_v,basin_v out=rain_comp_v WARNING: Vector map already exists and will be overwritten Patching vector map ... Patching vector map ... Building topology for vector map ... Registering primitives... 9 primitives registered 3643 vertices registered Building areas... 100% 1 areas built 1 isles built Attaching islands... 100% Attaching centroids... 100% Number of nodes: 9 Number of primitives: 9 Number of points: 0 Number of lines: 7 Number of boundaries: 1 Number of centroids: 1 Number of areas: 1 Number of isles: 1 Intersections at borders will have to be snapped Lines common between files will have to be edited The header information also may have to be edited v.patch complete. 2 vector maps patched rain_comp_v looks like this http://n2.nabble.com/file/n3568825/rain_comp_v.png > v.clean in=rain_comp_v out=rain_comp tool=break --o -- Tool: Threshold Break: 0.00e+00 -- WARNING: Vector map already exists and will be overwritten Copying vector lines... Rebuilding parts of topology... Building topology for vector map ... Registering primitives... 9 primitives registered 3643 vertices registered Number of nodes: 9 Number of primitives: 9 Number of points: 0 Number of lines: 7 Number of boundaries: 1 Number of centroids: 1 Number of areas: - Number of isles: - -- Tool: Break lines at intersections -- Rebuilding topology for output vector map... Building topology for vector map ... Registering primitives... 28 primitives registered 3662 vertices registered Building areas... 100% 1 areas built 1 isles built Attaching islands... 100% Attaching centroids... 100% Number of nodes: 28 Number of primitives: 28 Number of points: 0 Number of lines: 26 Number of boundaries: 1 Number of centroids: 1 Number of areas: 1 Number of isles: 1 >v.centroids rain_comp out=rain_cen option=add --o WARNING: Vector map already exists and will be overwritten Processing features... 0 new centroids placed in output map Copying attribute table(s)... Building topology for vector map ... Registering primitives... 28 primitives registered 3662 vertices registered Building areas... 100% 1 areas built 1 isles built Attaching islands... 100% Attaching centroids... 100% Number of nodes: 28 Number of primitives: 28 Number of points: 0 Number of lines: 26 Number of boundaries: 1 Number of centroids: 1 Number of areas: 1 Number of isles: 1 v.category complete. 0 features modified. Area is still 1 and centroid is 1. If i have understood it correctly, then we should have multiple area representing the isohyetal strips as output. Thanks Daljeet Micha Silver wrote: > > Hi Daljeet > > > daljeet wrote: > >> Hi Micha, >> >> I could create isohyetal lines using the suggested steps: >> >> > ... clipped... >> >> Following are the doubts/questions >> >> 1. I saw the
Re: [GRASS-user] how to calculate area of voronoi polygons considering the boundary of the catchment
The issue was that the contours vector was 3d. Now i could put the centroids and add the area within the boundaries. I am struck at how to associate the area (cat|area) with the associated isohyetal lines? Any idea. Thanks Daljeet daljeet wrote: > > Thanks. > > I am using the first method that you suggested. But it fails to create > centroids whereas there are multiple isohyetal strips now and each should > have been given the centroid. To give you the details on what i did. > > In real scenario, we will have the defined catchment area (which will be a > close polygon shaped vector) with rainfall measurements on various gauge > points (some gauge points will be within the catchment boundary and some > will be outside that catchment area, but within the region of the > catchment vector). Please correct me if I am wrong. > > I am simulating the above scenario by > a) making a xyz point data file. x,y being lat and long and z being the > measurement of rainfall. > b) catchment is represented by a vector (basin_v) > >> g.region vect=basin_v > > #import the xyz pt data >> v.in.ascii x=2 y=1 cat=0 input="rain_data" out="rainpoint_v" columns="x >> double precision, y double precision, rain_info double precision" fs="\t" >> skip=1 --o > >>MASK applied (which represents the raster of the catchment area with each cell value equal to 1) > >>v.surf.rst rainpoint_v zcol=rain_info elev=rain_rst --o > >>r.contour step=1 input=rain_rst output=rain_con_v > > At this stage, i have two seperate vectors, a) contour vector (rain_con_v) > which has the lines only b) vector representing the catchment area > (basin_v) whose topo details are as follows > >>v.info rain_con_v -t > nodes=7 > points=0 > lines=7 > boundaries=0 > centroids=0 > areas=0 > islands=0 > faces=0 > kernels=0 > primitives=7 > map3d=1 > > Please note the below output. This may be reason of failure. >>v.info basin_v -t > nodes=2 > points=0 > lines=0 > boundaries=1 > centroids=1 > areas=1 > islands=1 > faces=0 > kernels=0 > primitives=2 > map3d=0 > > Now, as you suggested, i need to apply the v.clean (with break) to create > the nodes at the intersection of isolines and boundary of the catchment > vector. > > And for the input of v.clean, I patched the above two vectors using > v.patch. Please correct if this is the right step or something else would > have been done? > >> v.patch input=rain_con_v,basin_v out=rain_comp_v > WARNING: Vector map already exists and will be overwritten > Patching vector map ... > Patching vector map ... > Building topology for vector map ... > Registering primitives... > 9 primitives registered > 3643 vertices registered > Building areas... > 100% > 1 areas built > 1 isles built > Attaching islands... > 100% > Attaching centroids... > 100% > Number of nodes: 9 > Number of primitives: 9 > Number of points: 0 > Number of lines: 7 > Number of boundaries: 1 > Number of centroids: 1 > Number of areas: 1 > Number of isles: 1 > Intersections at borders will have to be snapped > Lines common between files will have to be edited > The header information also may have to be edited > v.patch complete. 2 vector maps patched > > rain_comp_v looks like this > > http://n2.nabble.com/file/n3568825/rain_comp_v.png > >> v.clean in=rain_comp_v out=rain_comp tool=break --o > -- > Tool: Threshold > Break: 0.00e+00 > -- > WARNING: Vector map already exists and will be overwritten > Copying vector lines... > Rebuilding parts of topology... > Building topology for vector map ... > Registering primitives... > 9 primitives registered > 3643 vertices registered > Number of nodes: 9 > Number of primitives: 9 > Number of points: 0 > Number of lines: 7 > Number of boundaries: 1 > Number of centroids: 1 > Number of areas: - > Number of isles: - > -- > Tool: Break lines at intersections > -- > Rebuilding topology for output vector map... > Building topology for vector map ... > Registering primitives... > 28 primitives registered > 3662 vertices registered > Building areas... > 100% > 1 areas built > 1 isles built > Attaching islands... > 100% > Attaching centroids... > 100% > Number of nodes: 28 > Number of primitives: 28 > Number of points: 0 > Number of lines: 26 > Number of boundaries: 1 > Number of centroids: 1 > Number of areas: 1 > Number of isles: 1 > >>v.centroids rain_comp out=rain_cen option=add --o > WARNING: Vector map already exists and will be overwritten > Processing features... > 0 new centroids placed in output map > Copying attribute table(s)... > Building topology for vector map ... > Registering primitives... > 28 primitives registered > 3662 vertices registered > Building areas... > 100% > 1 areas built > 1 isles built > Attaching islands... > 100% > Attaching centroids... > 100% > Number of nodes: 28 > Number of
