HDF

NCSA (National Center for Supercomputing Applications) Hierarchical Data Format (HDF), a popular choice for complex raster scientific data.  Used mostly for images. Used widely in Earth Observation Satellite (EOS) projects such as EOS and SeaWiFS satellites.   HDF is a very complex format that can easily create thousands of components from a single HDF file.  It rarely provides projection information.

 

dlg_import_hdf.png

 

To import from HDF format:

 

  1. Choose File-Import from the main menu.

  2. In the Import dialog browse to the folder containing data of interest.

  3. Double-click the file ending in .hdf for the data of interest.

  4. One or more components, usually tables and images, as well as comments, will be created.

 

 

eg_import_hdf01_01.png

 

We can double-click on images that are created to view them.   The example .hdf file imported as numerous comments components (each one rather inefficiently containing only a few words, or one parameter value) with only one image and table created.

 

eg_import_hdf01_02.png

 

The image appears without using the correct projection.   That is a good reason to avoid using HDF format whenever possible in GIS work, to avoid the tedious work of finding out what coordinate system is supposed to be used and then assigning it.     The image also appears with very poor definition because we must use Style to assign the full ranges of values the data uses.

 

eg_import_hdf01_03.png  eg_import_hdf01_04.png

 

We use the Style panel in the Contents pane.    We begin by Ctrl-clicking each of the default R, G and B channels in turn to select them,, and then right-clicking either the 0 or 255 parameter in one of the ranges and choosing Full Range.  The system will recalculate the ranges to use the full range of values that appear in the channels, in this case from 0 to 65535.  We press Update Style.

 

 

eg_import_hdf01_05.png

 

That provides a more intelligible display.  We can further improve it by using Style to apply a palette.

 

eg_import_hdf01_06.png

 

We use the Style panel in the Contents pane to color the image using a palette.   Colors have been selected to provide a pseudo-NDVI appearance to the data.   We guess from the name of the file that it provides NDVI data, so we would like to color regions where it is likely there is more vegetation more green, and those with less vegetation more beige.

 

eg_import_hdf01_07.png

 

We press Update Style and the palette is applied.

 

eg_import_hdf01_08.png

 

We zoom in to take a closer look.  

Notes

This would be wonderful data but for the frustratingly primitive lack of coordinate system information in automated form.   Digging through the many comments we can puzzle out the coordinate system and assign it using Assign Initial Coordinate System, but it would be better in the 21st century for the format to do that for us.  

See Also

Style

 

Images

 

Assign Initial Coordinate System