DESCRIPTION

r.quantile.ref computes for each pixel the quantile ranking of the input value against the reference maps: values of 0, 0.5 and 1.0 respectively indicate that the input value corresponds with the minimum, median or maximum of the reference values. A value of -1 is assigned if the input value is smaller than the minimum and a value of 2 is assigned if the input value is larger than the maximum.

r.quantile.ref can be regarded as the inverse of r.series method=quantile: while r.series calculates the value for a given quantile, r.quantile.ref calculates the quantile for a given value. This is useful to compare e.g. current environmental conditions to a time series of historical environmental conditions.

EXAMPLE

Create some reference rasters: 
r.mapcalc "ref1 = 1"
r.mapcalc "ref2 = 2"
r.mapcalc "ref3 = 3"
r.mapcalc "ref4 = 5"
r.mapcalc "ref5 = 5"
r.mapcalc "ref6 = 5"
Create a test raster with cell value 4.5: 
r.mapcalc "test = 4.5"
Get the quantile of the test raster for the reference maps: 
r.quantile.ref input=test reference=ref1,ref2,ref3,ref4,ref5,ref6 output=test_quant
The quantile corresponding to the value 4.5 is 0.55. Create a test raster with cell value 5: 
r.mapcalc "test = 5"
Get the quantile of the test raster for the reference maps: 
r.quantile.ref input=test reference=ref1,ref2,ref3,ref4,ref5,ref6 output=test_quant
The quantile corresponding to the value 5 is 0.8.

SEE ALSO

r.quantile, r.series

AUTHOR

Markus Metz

Last changed: $Date$