(Source: National Snow and Ice Data Center's (NSIDC) Introduction to HDF-EOS. (no date) Retrieved May 2, 2003, from http://nsidc.org/data/stevek/intro.html)
Hierarchical Data Format (HDF) is the standard data format for all NASA Earth Observing System (EOS) data products. HDF is a multi-object file format developed at the National Center for Supercomputing Applications (NCSA) at the University of Illinois.
NCSA developed HDF to assist users in the transfer and manipulation of scientific data across diverse operating systems and computer platforms, using FORTRAN and C calling interfaces and utilities. HDF supports a variety of data types: n-Dimensional scientific data arrays, tables, text annotations, several types of raster images and their associated color palettes, and metadata. The HDF library contains interfaces for storing and retrieving these data types in either compressed or uncompressed formats.
For each data object in an HDF file, predefined tags identify the type, amount, and dimensions of the data; and the file location of various objects. The self-describing capability of HDF files helps users to fully understand the file's structure and contents from the information stored in the file itself. A program interprets and identifies tag types in an HDF file and processes the corresponding data. A single HDF file can also accommodate different data types, such as symbolic, numerical, and graphical data; however, raster images and multidimensional arrays are often not geolocated. Because many earth science data structures need to be geolocated, NASA developed the HDF-EOS format with additional conventions and data types for HDF files.
HDF-EOS supports three geospatial data types (grid, point, and swath), providing uniform access to diverse data types in a geospatial context. The HDF-EOS software library allows a user to query or subset the contents of a file by earth coordinates and time (if there is a spatial dimension in the data). Tools that process standard HDF files will also read HDF-EOS files; however, standard HDF library calls cannot access geolocation data, time data, and product metadata as easily as with HDF-EOS library calls.
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