ExGrib.Grib2.Section5.Templates.GridPointDataSimplePackingWithLogarithmPreProcessing (ex_grib v0.0.1) View Source
Template 5.61
Grid point data simple packing with logarithm pre processingng
Notes:
(1) The template is approriately designed for data sets with all non-negative values and a wide variability range (more then 5 orders of magnitude). It must not be used for data sets with negative values or smaller variability range.
(2) A logarithm pre-processing algorithm is used to fit the variability range into one or two order of magnitudes before using the simple packing algorithm. It requires a parameter (B) to assure that all values passed to the logarithm function are positive.Thus scaled values are Z=ln (Y+B), where Y are the original values, ln is the natural logarithm (or Napierian) function and B is chosen so that Y+B>0.
(3) Best pratice follows for choosing the B pre-processing parameter. (a) If the data set minimum value is positive, B can be safely put to zero. (b) If the data set minimum is zero, all values must be scaled to become greater than
zero and B can be equal to the minimum positive value in the data set.
(4) Data shall be packed using Data template 7.
https://www.nco.ncep.noaa.gov/pmb/docs/grib2/grib2_doc/grib2_temp5-61.shtml