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/