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6.7 RIS8 Backward Compatibility Issues

6.7.1 Attribute "long_name" Included in HDF for netCDF Compatibility

In several routines of the RIS8 interface, the value returned by label is the value of the attribute named "long_name" and that the value returned by coordsys is the value of the attribute named "cordsys".

This was done in order to provide HDF with the ability to read netCDF files. While this aspect of HDF functionality will not affect its ability to read HDF data files written by programs compiled with earlier versions of HDF, it is advisable for HDF users to know this to be aware of the significance of the "long_name" and "cordsys" attribute names in a list of attributes.

6.7.2 Raster Image Group Implementation with New RIS8 Tags

As HDF has evolved, a variety of structures have been used to store raster image sets. For instance, HDF first began grouping 8-bit raster images together with dimensions and palettes by insuring that their reference numbers fell in a certain pattern. This method of organizing raster images quickly lead to very complicated collections of images, dimension records, and palettes, and eventually was replaced by an specific grouping structure known as a Raster Image Group, or RIG, with a completely new set of tags.

To maintain backward compatibility with older versions of HDF, the RIS8 interface supported by HDF version 4.1 and later recognizes raster images stored using either set of HDF tags. Details on the different tags and structures used to store raster images can be found in the HDF Specifications and Developer's Guide v3.2 from the HDF WWW home page at http://hdf.ncsa.uiuc.edu/.



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HDF User's Guide - 07/21/98, NCSA HDF Development Group.