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#### 4.1.1.4 CDF

NASA's Common Data Format, described at https://cdf.gsfc.nasa.gov/, is a binary format for storing self-described data. It is typically used to store tabular data for subject areas like space and solar physics.

CDF does not store tables as such, but sets of variables (columns) which are typically linked to a time quantity; there may be multiple such disjoint sets in a single CDF file. This reader attempts to extract these sets into separate tables using, where present, the `DEPEND_0` attribute defined by the ISTP Metadata Guidelines. Where there are multiple tables they can be identified using a "`#`" symbol at the end of the filename by index ("`<file>.cdf#0`" is the first table) or by the name of the independent variable ("`<file>.cdf#EPOCH`" is the table relating to the `EPOCH` column).

Files in this format may contain multiple tables; depending on the context, either one or all tables will be read. Where only one table is required, either the first one in the file is used, or the required one can be specified after the "`#`" character at the end of the filename.

This format can be automatically identified by its content so you do not need to specify the format explicitly when reading CDF tables, regardless of the filename.

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TOPCAT - Tool for OPerations on Catalogues And Tables
Starlink User Note253
TOPCAT web page: http://www.starlink.ac.uk/topcat/
Author email: m.b.taylor@bristol.ac.uk
Mailing list: topcat-user@jiscmail.ac.uk