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The variable in an EPIC data file is described by a numeric code in the data file. The epic.key file contains information about each numeric variable code. Each line of the epic.key file has 7 fields divided by the character ``:''. The fields contain the variable code, a short name, a long name, the generic name, the units of the variable, the format for printing the data values (in Fortran format notation), and a comment field. The short, long and generic names are character strings. The short name is four characters or less, and is suitable for use as a title for a column on a data listing. The long name is intended to be used in a label, such as an axis label on a graph. The generic name is used to access data from within the nccalc netCDF calculator, which is linked with the PPLUS graphics package. The EPIC variable key code is a positive integer with 4 or fewer digits, and is a unique identifier for the variable. The comment field is optional, and includes information about the variable, such as ``Temperature in degrees Centigrade on the 1968 temperature scale''. The only field which is not optional is the numeric variable code. For example, Air Temperature in a data file has numeric variable code of 21, short name of ``AT'', long name of ``Air Temperature, C'', generic name of ``atemp'', units of ``C'', format of ``f10.2'', and a comment field of ``1968 standard''. This file can be edited to add newly defined variables.
The epic.key must be presented (accessible) when you run any application uses EPIC system routines. The file epic.key is used by EPIC system routines to identify or locate the variables in a data file. It is also used by PPLUS to label plots automatically. If the data file is in Classic EPIC format, then the data file contains only numeric variable codes to identify each variable in the file, and all other information about the variable is found in the epic.key file by the EPIC programs and by the PPLUS graphics package. It is required that all variable codes used in a Classic EPIC data file must be defined in the epic.key file. For netCDF formatted data files, when reading, the information in the epic.key file is used only when a variable code attribute is found but lack of other variable information in the data file. At the time when the data file is written, this information can be included in the netCDF file by simply specifying the appropriate numeric variable key code. The EPIC system library will extract the other information from the epic.key file for inclusion in the data file as attributes. Alternatively, an application program writing the netCDF file can set some or all of these attributes in the data file directly, without specifying a numeric variable key code. It is possible to write a netCDF file which omits the numeric code and these attributes entirely, but this omission will result in a lack of information available to EPIC programs and also to PPLUS.
In UNIX system, the epic.key is normally installed in /usr/local/lib or the directory specified in the Makefile at the time when EPS library is compiled. If this file is moved from its original directory to a new location, user must set the environment variable ``EPS_EPICKEY'' pointing to the new directory, for example, ``setenv EPS_EPICKEY /home/tao/eps'' indicates that epic.key file is currently located in /home/tao/eps.
Click here to see the current EPIC.KEY file list.
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