HDF
What is HDF?
HDF stands for the Hierarchical Data Format. NCSA HDF allows researchers
to manage scientific data with a data storage and retrieval system
that facilitates support for scientific data and metadata on a range
of hardware platforms. HDF-supported data and metadata include
multidimensional gridded data, raster images, polygonal mesh data,
multivariate datasets, finite-element data, non-Cartesian coordinate
data, and text. HDF supports a hierarchical grouping structure called
Vset that lets researchers organize data objects within HDF files to
fit their views of how the objects go together. Most NCSA scientific
visualization software,and many other applications, support HDF files.
HDF Raster Images
HDF supports the storing of both 8-bit and 24-bit raster images. As
well as storing information about the dimensions and palette of a
raster image, HDF supports raster image compression. In previous
versions of HDF, Run-length encoding and Imcomp compression were both
supported. With HDF 3.3 JPeg compression is also available.
HDF Scientific Data Sets
Scientific Data Sets (SDSs) are useful for storing n-Dimensional
gridded data. The actual data in the dataset can be of any of the
"standard" number types: 8, 16 and 32bit signed and unsigned integers
and 32 and 64bit floating point values. In addition, a certain amount
of meta-data can be stored with an SDS including:
- The coordinate system to use when interpreting or displaying the data.
- Scales to be used for each dimension.
- Labels for each dimension and the dataset as a whole.
- Units for each dimension and the data.
- The valid max and min values for the data.
- Calibration information for the data.
- Fill or missing value information.
HDF Annotations
Any object in an HDF file can have annotations associated with
it. There are a number of types of annotations:
Labels are assumed to be short strings giving the "name" of a data object.
- Descriptions are longer text segments that are useful for giving more indept information about a data object
- File annotations are assumed to apply to all of the objects in a single file.
HDF Vset Interfaces
The Vset module provides interfaces to two basic HDF building
blocks. Vgroups are generic grouping elements allowing a user to
associate related objects within an HDF file. As Vgroups can contain
other Vgroups, it is possible to build a hierarchical file. Vdatas
are generic list objects. Data is organized into 'fields' within each
Vdata. Each field is identified by a unique 'fieldname'. The type of
each field may be any of the basic number types that HDF
supports. Fields of different types may exist within the same Vdata.
By combining Vdatas in Vgroups it is possible to represent higher
level data constructs: mesh data, multi-variate datasets, sparse
matrices, finite-element data, spreadsheets, splines, non-Cartesian
coordinate data, etc.
How to Use
To use HDF you will need to add the following to your .tcshrc file.
source /usr/local/Standards/hdf
Availability
HDF is available on the Suns and the SGIs.
Press here to return to the User's Guide Menu.