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Chapter 8: HDF-EOS extensions


8.1 Overview

In 1993 NASA chose NCSA's HDF format to be the standard file format for storing data from the Earth Observing System (EOS), which is the data gathering system of sensors (mainly satellites) supporting the Global Change Research Program.

Since NASA's selection of HDF, NCSA has been working with NASA to prepare for the enormous data management challenges that will come when the system is fully functional. This has included the development of a specialized form of HDF called HDF-EOS, which deals specifically with the kinds of data that EOS produces. "Terra", the first satellite to fly as part of the EOS, was launched in December, 1999, and began delivering data officially in April, 2000. The next satellite (Aqua), is likely to launch in 2001, and the one after that (Aura) in 2002.

The HDFView tool has been extended in this version for browsing and editing HDF-EOS2 and HDF-EOS5 files. HDFView allows users to browse through any HDFEOS file; starting with a tree view of all top-level objects in an HDF file's hierarchy, such as Grid and Swath data. HDFView allows a user to descend through the hierarchy and navigate among the file's data objects. 

 The following figure shows package structure of the HDFView with the HDF-EOS2 and HDF-EOS5 extensions.


Figure 8.1 HDFView HDF-EOS Class Packages

8.2 Features

HDFView allows viewing of specific HDF-EOS objects, such as Grid and Swath, as well as other HDF-EOS metadata.

The Following is a list of the browsing features of HDFView for HDF-EOS data.

8.3 HDF-EOS Metadata

To see the metadata of a data object, you click the right button of the mouse on the data object. The metadata dialog pops up with metadata information appropriate for the data object.  The following information is displayed for each type of HDF-EOS data object.


Figure 8.2 General Properties of Swath Dataset

Figure 8.3 General Properties of Grid Dataset

 

To view file attributes, right-click the file node (the root group) to popup the metadata dialog.


Figure 8.4 File Properties

 

8.4 HDF-EOS Object Model

When you open an HDF-EOS file with HDFView, you see the tree structure of an HDF-EOS file, showing the objects and their groupings. You can select an object from the tree to view its content.  HDFView is built on a common HDF object model and suports both versions of HDF-EOS. The HDF object model was designed in such a way that the HDF-EOS2 and HDF-EOS5 objects interact with users through a common object layer so the user interface design will be independent of the file format.

This chapter provides basic information of the HDF-EOS object model. For more details of the object model, visit the HDF-EOS Information Center website at http://newsroom.gsfc.nasa.gov/sdptoolkit/userguide.html

The HDF Object Package is a Java package which implement HDF-EOS2 and HDF-EOS5 data objects in an object-oriented form. The HDF Java Object Package provides common standard Java APIs to access both HDF-EOS2 and HDF-EOS5 files.

The HDF Object Package is NOT a "wrapper" for the native HDF libraries and it requires the HDF-EOS2 and HDF-EOS5 wrapper. The HDF-EOS2 and HDF-EOS5 wrappers are separate HDF Java products. For details of the HDF4 and HDF5 native interfaces, read the HDF-EOS User Guides at http://newsroom.gsfc.nasa.gov/sdptoolkit/userguide.html.

The HDF object package has two major goals. First, it simplifies the process of reading information from or writing data to file because the details of accessing to the HDF library are encapsulated into respective classes. Second, HDF-EOS2 and HDF-EOS5 objects are inherited from the same common object and interface. Applications can use of the HDF Object Package to access objects from either HDF-EOS2 or HDF-EOS5 in a uniform way, without accessing the libraries directly. The following diagram explains the relationship of the object package, HDF JNI and applcation.

HDF Applcations <==> HDF Object Package <==> HDF-EOS2/HDF-EOS5 Java Wraper (JNI4/5) <==> HDF File

 

 

8.5 The TreeView

The Tree shows the objects in each open file, and supports navigation and editing of the objects. Muliple files can be viewed and edited, and both HDF-EOS2 and HDF-EOS5 files can be opened. The viewing operations work for both HDF-EOS2 and HDF-EOS5, but editing is currently disabled.

The following icons are used to represent HDF-EOS objects:

The metadata dialog appears by clicking the object (icon) in the tree with the right button or select the "Properties" command from the "Object" menu.

8.6 For Further Information

General information about HDF-EOS is available at: http://hdf.ncsa.uiuc.edu/hdfeos.html

General information about HDF and HDF4 and HDF5 are available at: http://hdf.ncsa.uiuc.edu/index.html

Information about the HDFView tool and related products is available at:

http://hdf.ncsa.uiuc.edu/hdf-java-html/

Questions and feedback may be sent to: hdfhelp@ncsa.uiuc.edu


 

Updated 4/18/2006