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The HDF format
What is HDF ?
HDF stands for Hierarchical Data Format. It is
developed by NCSA (National Center for Supercomputing Applications) and its
first aim was to help scientists to work and exchange graphical and numerical
data.
It can be seen as three interface layers built upon a physical file
format. At its lowest level, it is a physical file format for
storing data like any other format. At its highest level, HDF is a
collection of utilities and applications for manipulating data in HDF files. Between
these levels, HDF is a software library. A user doesn't have to know how is
implemented the lowest level to manipulate data stored in a HDF format.
Its main features are :
 | It is a versatile file format : it supports different data
models. Each data model defines a specific type of data and provides a
convenient interface for reading, writing and organizing a unique set of
data elements. HDF can stores several different types of data in the same
file or in separate files (multi-file interface). |
| It is a self-describing format, allowing an application to
interpret the structure and contents of a file without any outside
information. |
| It is a flexible file format : related objects can be grouped
together and then accessed as a group or as individual objects. There are
pre-defined sets and users can create their own grouping structure (vgroup
feature). |
| It is an extensible file format : it can accomodate new data
models. |
| It is a portable file format : HDF files can be shared across
plateforms. |
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What is the HDF library ?
HDF currently supports the following data structures types :
| Raster images (general, 8-bit, 24-bit), |
| color palettes, |
| text entries, |
| SDS (scientific data sets) : multi-dimensional arrays to
store items of the same type (floats, integers...), |
| Vdata : two-dimensional array to store items of different
types, |
| Vgroup : a structure for associating sets of data objects. |
The HDF library contains two parts : the base library and the multi-file
library. HDF functions can be called from C and Fortran user application program.
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Usefull addresses on HDF
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