wgrib2: set_scaling
Introduction
The values at the grid points points are stared in a general format,
Y = (R + i*2**B)*(10**D)
R = reference value
i = integer, 0..2**N1
N = binary bit precision
B = binary scaling
D = decimal scaling
There are 3 sytems for storing the number which I have called
ECMWF convention: D = 0, N = parameter
Y = R + i*2**B
R = reference value
i = integer, 0..2**N1
N = binary bit precision, a parameter
B = binary scaling, determined by grib routines
NCEP convention: B = parameter, D = parameter
R = reference value
i = integer, 0..2**N1
N = binary bit precision, determined by grib routines
B = binary scaling, a parameter
D = decimal scaling, a parameter
Note, global model uses a variant: B = 0, D = parameter
Both the ECMWF and NCEP conventions have their advantages and
disadvantages. The ECMWF method is easier to use, you just
set the binary precision to 12 or 16 bits for all variables
and you are done. With the NCEP convention, you have to
set the scaling for each variable separately. For some variables
such as specific humidity, the scaling should be pressure
dependent. On the other hand, if you are trying to get the smallest
files, the NCEP convention is better. For example, you want to
get the RH to the nearest integer. With the NCEP method, you simply
set D = B = 0. For general use, I suggest that you use the ECMWF
convention because people time is usually more valuable than disk space.
Ok, I value my time more than a few GB. On the othe hand, I've been
involved with more than my share of projects were disk space
has been the critical issue.
Usage
The set_scaling option is used to
set wgrib2 to encode data using the NCEP convention.
set_scaling D B
D = decimal scaling
B = binary scaling
See alse:
set_bin_prec
set_grib_max_bits
