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The Heirarchy

The ``H'' in HDF stands for ``Heirarchical'' and this describes how HDF files are structured. An HDF file can be likened to a file system. At the root of the file system is a period (``.'') or a slash (``/'') and the file may consist of an arbitrary number of levels of data, like subdirectories in a file system. For example, if a NOAA satellite image containing several spectral bands of data are stored in this manner, one way of doing so could look like this:

.
/NOAA 14/
/NOAA 14/info
/NOAA 14/info/xsize
/NOAA 14/info/ysize
/NOAA 14/Channel 1/
/NOAA 14/Channel 2/
/NOAA 14/Channel 3/
where info is an object containing header information. The same strategy could be used to store several polar scans of weather radar data, for example.

Alternatively, a numerical weather prediction model state could be represented in part using GRIB descriptors like this:

.
/Level 0/
/Level 0/Type 105/
/Level 0/Type 105/Parameter 11/
/Level 0/Type 102/
/Level 31/
/Level 31/Type 109/
/Level 31/Type 109/Parameter 11/
Or, why not a point from a weather station containing wind speed and direction values:
.
/WMO 02064/
/WMO 02064/dd/
/WMO 02064/ff/
/WMO 02036/




2000-08-08