Computing composite indices (
wsim_composite utility computes Composite Indices from multiple surplus and deficit input variables.
The composite indices are output to a netCDF file with the following variables:
the worst (most positive) return period of all input surplus variables
a coded variable indicating which of the surplus variables was responsible for the composite surplus indicator value
the worst (most negative) return period of all input deficit variables
a coded variable indicating which of the deficit variables was responsible for the composite deficit indicator value
the greater magnitude of
deficit, whenever both of these indices have a magnitude higher than a specified threshold
Usage is as follows:
Usage: wsim_composite \ (--surplus=<file>)... \ (--deficit=<file>)... \ --both_threshold=<value> \ [--mask=<file>] \ --output=<file>
--deficit arguments are used to specify variables that should be considered in computing the composite surplus and deficit indices.
each argument may refer to more than one variable, and each argument may be provided multiple times. The WSIM variable definition notation is fully supported.
--both_threshold argument specifies the minimum magnitude of the composite surplus and deficit indices for a pixel to be considered to simultaneously experience surplus and deficit.
--mask allows an optional mask to be defined, so that all composite indices have the same maximum extent even if the input datasets do not.
As a more complete example, the following command was is used to produce the WSIM composite indices for January 2017 from multiple raster inputs:
./wsim_composite.R \ --deficit "~/freq/PETmE_freq_trgt201701.img::1@fill0@negate->Neg_PETmE" \ --deficit "~/freq/Ws_freq_trgt201701.img::1->Ws" \ --deficit "~/freq/Bt_RO_freq_trgt201701.img::1->Bt_RO" \ --surplus "~/freq/Bt_RO_freq_trgt201701.img::1->Bt_RO" \ --surplus "~/freq/RO_mm_freq_trgt201701.img::1->RO_mm" \ --mask "~/freq/Ws_freq_trgt201701.img" \ --both_threshold 3 \ --output "/tmp/composite_201701.nc"
A few points are worth noting in this example:
Bt_ROvariable is considered in computation of both the surplus and deficit indices.
PETmEvariable is transformed by filling NODATA values with zero, and then negating all values.
Wsvariable was used as a mask for the composite indices. If this were not done, the composite deficit would be populated in all pixels, because of the transformation done to