Re: [GRASS-user] Using r.quantile result with r.recode
Pedro Venâncio wrote: > > r.recode will treat boundary values as belonging to the upper range, > > e.g. in the above example, 6.0 will get recoded to 2. > > > So we can not use directly the result of r.quantile with -r flag in r.recode, > right? > > In the example, 6 should be recoded to 1, right? For real data, most of the boundary values won't be actual values from the input data, but values derived from interpolating two adjacent values. In that situation, it doesn't matter how r.recode handles boundary values. -- Glynn Clements ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] Using r.quantile result with r.recode
Hi Glynn, > - Original Message - > From: Glynn Clements > r.recode will treat boundary values as belonging to the upper range, > e.g. in the above example, 6.0 will get recoded to 2. So we can not use directly the result of r.quantile with -r flag in r.recode, right? In the example, 6 should be recoded to 1, right? Thank you very much! Best regards, Pedro Pedro Venâncio wrote: > Thank you very much for your answer! > > My question lies precisely in the need to know if a quantile value > which falls as the upper limit for one range and the lower limit of > the next, should belong to the class anterior or posterior. > > > For example, assuming that r.quantile (with -r flag) gives this result: > > 2:6:1 > 6:8:2 > 8:12:3 > 12:20:4 > 20:873:5 > > the value 6 should belong to the first class or second? r.recode will treat boundary values as belonging to the upper range, e.g. in the above example, 6.0 will get recoded to 2. This behaviour stems from Rast_fpreclass_get_cell_value() in lib/raster/fpreclass.c, and isn't configurable (i.e. there's no way that r.recode's behaviour could be modified without modifying the fpreclass functions). -- Glynn Clements ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] Using r.quantile result with r.recode
[CC to grass-dev for discussion] Pedro Venâncio wrote: > Thank you very much for your answer! > > My question lies precisely in the need to know if a quantile value > which falls as the upper limit for one range and the lower limit of > the next, should belong to the class anterior or posterior. > > > For example, assuming that r.quantile (with -r flag) gives this result: > > 2:6:1 > 6:8:2 > 8:12:3 > 12:20:4 > 20:873:5 > > the value 6 should belong to the first class or second? r.recode will treat boundary values as belonging to the upper range, e.g. in the above example, 6.0 will get recoded to 2. This behaviour stems from Rast_fpreclass_get_cell_value() in lib/raster/fpreclass.c, and isn't configurable (i.e. there's no way that r.recode's behaviour could be modified without modifying the fpreclass functions). -- Glynn Clements ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] Using r.quantile result with r.recode
Hi Glynn, Thank you very much for your answer! My question lies precisely in the need to know if a quantile value which falls as the upper limit for one range and the lower limit of the next, should belong to the class anterior or posterior. For example, assuming that r.quantile (with -r flag) gives this result: 2:6:1 6:8:2 8:12:3 12:20:4 20:873:5 the value 6 should belong to the first class or second? Thank you very much Glynn! Best regards, Pedro - Original Message - From: Glynn Clements Pedro Venâncio wrote: > I have a doubt about using the r.quantile output with r.recode. > > r.quantile returns the upper limit value corresponding to each > class, right? r.quantile calculates quantile values. If you use the -r flag, each value is used as the upper limit for one range and the lower limit of the next. The map's total range sets the lower limit of the first range and the upper limit of the last range. If the number of values is an exact multiple of the number of divisions (e.g. 4 for quantiles, 10 for deciles, etc), the quantile will be one of the input values, otherwise it will be linearly interpolated between two adjacent values. It's possible that there should be a -1 in the calculation; currently, if you calculate the deciles of the 100 distinct values 0-99 inclusive, the results will be 10,20,...,90, so the ranges will be 0-10,10-20,...,90-99. > But r.recode uses r.quantile result as closed interval in the lower > value and open interval in the upper value. r.recode does whatever the Rast_fpreclass_* functions do. Which is to scan the rules from highest to lowest and stop on the first match. So for a value which is on the boundary between ranges, the upper range will be chosen. > But this is not correct. According to quantiles method, the reclassification > should be as follows: > > ]2.00:6.00] -> 1 > ]6.00:8.00] -> 2 > ]8.00:12.00] -> 3 > ]12.00:20.00] -> 4 > ]20.00:872.727295] -> 5 > > or am I wrong? I think that if the number of values is an exact multiple of the number of divisions, r.quantile+r.recode should result in each range having exactly the same number of values. But I'm not sure whether it's r.quantile, r.recode[1] or both which need to be fixed. [1] More precisely, the Rast_fpreclass_* functions. -- Glynn Clements ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] Using r.quantile result with r.recode
Pedro Venâncio wrote: > I have a doubt about using the r.quantile output with r.recode. > > r.quantile returns the upper limit value corresponding to each > class, right? r.quantile calculates quantile values. If you use the -r flag, each value is used as the upper limit for one range and the lower limit of the next. The map's total range sets the lower limit of the first range and the upper limit of the last range. If the number of values is an exact multiple of the number of divisions (e.g. 4 for quantiles, 10 for deciles, etc), the quantile will be one of the input values, otherwise it will be linearly interpolated between two adjacent values. It's possible that there should be a -1 in the calculation; currently, if you calculate the deciles of the 100 distinct values 0-99 inclusive, the results will be 10,20,...,90, so the ranges will be 0-10,10-20,...,90-99. > But r.recode uses r.quantile result as closed interval in the lower > value and open interval in the upper value. r.recode does whatever the Rast_fpreclass_* functions do. Which is to scan the rules from highest to lowest and stop on the first match. So for a value which is on the boundary between ranges, the upper range will be chosen. > But this is not correct. According to quantiles method, the reclassification > should be as follows: > > ]2.00:6.00] -> 1 > ]6.00:8.00] -> 2 > ]8.00:12.00] -> 3 > ]12.00:20.00] -> 4 > ]20.00:872.727295] -> 5 > > or am I wrong? I think that if the number of values is an exact multiple of the number of divisions, r.quantile+r.recode should result in each range having exactly the same number of values. But I'm not sure whether it's r.quantile, r.recode[1] or both which need to be fixed. [1] More precisely, the Rast_fpreclass_* functions. -- Glynn Clements ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
[GRASS-user] Using r.quantile result with r.recode
Hi, I have a doubt about using the r.quantile output with r.recode. r.quantile returns the upper limit value corresponding to each class, right? But r.recode uses r.quantile result as closed interval in the lower value and open interval in the upper value. In other words, assuming that r.quantile returns the following result: 2.00:6.00:1 6.00:8.00:2 8.00:12.00:3 12.00:20.00:4 20.00:872.727295:5 r.recode will use these data as follows: [2.00:6.00[ -> 1 [6.00:8.00[ -> 2 [8.00:12.00[ -> 3 [12.00:20.00[ -> 4 [20.00:872.727295[ -> 5 But this is not correct. According to quantiles method, the reclassification should be as follows: ]2.00:6.00] -> 1 ]6.00:8.00] -> 2 ]8.00:12.00] -> 3 ]12.00:20.00] -> 4 ]20.00:872.727295] -> 5 or am I wrong? Thanks! Best regards, Pedro Venâncio ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
