CDF Library Version 2.6 Available

Volume 12, Number 1, March 1996
by Gregory Goucher

Version 2.6 of the Common Data Format (CDF) library, which has been under development for the last several months, is scheduled for an alpha release in early March 1996. The new features will consist of data compression and sparse records. There will be three compression algorithms supported under the alpha release: Huffman, Adaptive Huffman, and Run Length Encoding of Zero's. Also, CDF staff are currently working with Goddard's Dr. Pen-Shu Yeh (Code 738.3) with the Rice algorithm and expect to support that compression technique in the near future. When creating a CDF the user will have the option of compressing an entire CDF or selected variables within the CDF. In addition to the new features, enhancements have been made to the internal indexing scheme of the library in an attempt to provide more efficient and higher throughput for data access.

NSSDC and the Space Physics Data Facility (SPDF) have developed a World Wide Web (WWW) -based data system called CDAWeb (available via the URL for providing enhanced access to scientific data in CDFs. CDAWeb allows the user to select variables from CDF data files and quickly make line plots, spectrograms, radar plots, images, etc. CDAWeb uses a forms-based WWW interface with a Perl engine back-end on a DEC Alpha workstation that queries a text file (generated by an Interactive Data Language [IDL] program) of metadata, lists of CDFs, time ranges, variable information, etc. The data are read into IDL using a sophisticated set of routines for handling International Solar-Terrestrial Physics (ISTP)-compliant CDFs. The selected data are then plotted in IDL according to rules for choosing the best type of plots. The plots are converted to Graphics Interchange Format (GIF) images and sent back in an HTML page. The pages are all created on-the-fly based on the data base and user selections.

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Author:Miranda Beall
Curators: Erin Gardner and Miranda Beall
Responsible Official: Dr. Joseph H. King, Code 633
Last Revised: 21 Nov 1996 [EDG]