View source for Climate Data Operators

[[de:Climate Data Operators]]
==about CDO==
The Climate data operators (CDO) software is a large collection of operators to analyse and process climate and  NWP model data. CDO was developed by  [https://code.zmaw.de/projects/cdo Max-Planck-Institut für Meteorologie] and is part of the „European Network for Earth System Modelling“ as a free package under GPL terms.  CDO has the same set of processing functions for GRIB  and NetCDF datasets in one package. Moreover, the Climate Data Interface [CDI] can be used for file format independent access. The local MPI-MET data formats SERVICE, EXTRA and IEG are also supported.
== The main CDO features ==
*More than 700 operators available
*Modular design and easily extendable with new operators
* Very simple UNIX command line interface
* A dataset can be processed by several operators, without storing the interim results in ﬁles
* Most operators handle datasets with missing values
* Fast processing of large datasets
* Support of many diﬀerent grid types
* Tested on many UNIX/Linux systems, Cygwin, and MacOS-X
==CDO operators classes==
CDO Operators are  simple functions  which can be grouped in different classes. The relevant operators classes for the BAW are listed and briefly described here (from the official documentation): 
*'''Information''' Operators to print information about datasets. All operators print there results to standard output.
*'''File operations'''  Operators to perform operations on files like copy, replace, cat, merge and split.
*'''Selection''' Operators to select time steps, fields or a part of a field from a dataset.
*'''Comparison'''  Operators  to compare datasets. The resulting field is a mask containing 1 if the comparison is true and 0 if not.
*'''Modification'''  Operators  to modify the metadata, fields or part of a field in a dataset.
*'''Arithmetic'''  Operators to arithmetically process datasets. Amongst others, one can add, subtract, multiply or divide a constant.  The direct processing of fields is also possible.  Moreover, time series can similarly be added, subtracted, multiplied or divided. 
*'''Statistical values'''  Operators to compute statistical values of datasets like  minimum, maximum, sum, mean, average, median,  variance, standard deviation, percentiles and histograms.
*'''Interpolation''' Operators to interpolate datasets. ieren. There are several operators to interpolate horizontal fields to a new grid. Some of those operators can handle only 2D fields on a regular rectangular grid. Vertical interpolation of 3D variables is possible from hybrid model levels to height or pressure levels. Interpolation in time is possible between time steps and years.

*'''Import/Export'''  Operators to import and export data files which cannot read or write directly with CDO like binaries or  ASCII datasets. 
== Examples of use at BAW==
The present example will show how a COSMO-EU meteo file in GRIB2 format is converted to  NetCDF and then further processed . Fort the sake of simplicity, all input files will be denoted by ifile and accordingly, all output files will be denoted by ofile.
* Convert to NetCDF:
cdo -t cosmo002 -f nc copy ifile.grib ofile.nc 
* Select variables:
cdo select,name=U,V,PMSL  ifile  ofile 
* Rename variables:
cdo chname,PMSL,slp,U,u10,V,v10  ifile ofile 
*Set a new Missing_value / Fill_value:
cdo setmissval,999.99  ifile ofile 
* Calculate the wind velocity magnitude:
cdo expr,vel=sqrt(u10^2+v10^2); ifile ofile 

== Installed versions ==
* Linux: cdo-1.7.2 from 28.06.2016
* Windows: not available

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