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HOME > Monitoring_and_Data > Oceanic and Atmospheric Data > Reanalysis: Atmospheric Data > pywgrib2_s: conventions

pywgrib2_s: conventions


What is a convention? In the year 2020, a convention is a gathering to decide who runs for political office. In bridge, a convention is an understanding that certain artifical bids have special meanings. For example, a opening 4 no trump bid asks the partner to disclose the number aces in his hand. The pywgrib2_s conventions are more like the bridge conventions.

Optional Parameter name starts with an uppercase

The optional parameter expects a logical value, and the default value is False.

Optional Parameter has a default value of "" (empty string)

The optional parameter expects a string value, and an empty string turns off the option.

Optional Parameter has a default value of None

The optional parameter expects something besides a string or logical value. It may exoect a number, a numpy array, or mutiple types of input.

Undefined Grid Values

Most reasonable computers have floating values that can be NaN (not a number). Using NaN can be a problem because "if (x == NaN)" is not the way to test if x is a NaN. Pywgrib2_s uses the numpy.nan for the NaN. Some codes may be based on wgrib2 scripts which use 9.999e20 as the value for undefined grid point value. You can change pwgrib2_s to use the wgrib2 convention by setting pywgrib2_.s.use_numpy.nan to False. Note that numpy.nan is not the same as math.nan; for example (math.nan is numpy.nan) is false.

Numpy Arrays

The grid values, lat and lon arrays are returned as numpy arrays. The arrays are in Fortran order, and in WE:SN order. In english,
  • a[i+1,j] is stored after a[i,j] in memory
  • for a lat-lon grid: a[i,j] and a[i+1,j] have the same latitude
  • for a lat-lon grid: a[i+1,j] is east of a[i,j] by delta-longitude degrees
  • for a lat-lon grid: a[i,j] and a[i,j+1] have the same longitude
  • for a lat-lon grid: a[i,j+1] is north of a[i,j+1] by delta-latitude degrees


Change the global variable pywgrib2_s.debug to True.

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Page created July 12, 2020
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