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Source: http://hdfeos.org/workshops/ws01/presentations/UAH/matt.ppt
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The University of Alabama in Huntsville
UAH 8-10 September 1997
Dataset Independent Subsetting
A Dataset Independent Subsetting Prototype
http://minnie.cs.uah.edu/
Matthew R. Smith - matt.smith@msfc.nasa.gov
Bruce Beaumont
Dr. Sara J. Graves
The University of Alabama in Huntsville
Information Technology & Systems Laboratory
The University of Alabama in Huntsville
UAH 8-10 September 1997
Outline
�Context
�Purpose
�Design
�Functionality
�Web pages
�Future
�Summary
The University of Alabama in Huntsville
UAH 8-10 September 1997
Context
�NASA’s Mission to Planet Earth (MTPE)
� Earth Observing System (EOS)
� Data and Information System (DIS)
EOSDIS Core System (ECS) Contractor:
Hughes Information Technology Systems
� Design and Implement a prototype dataset-
independent subsetter
The University of Alabama in Huntsville
UAH 8-10 September 1997
Subsetting?
l Goal: to provide a science data user with only
the data they request as quickly as possible.
l Benefits science data users and data centers:
- reduces analysis time by reducing amount of data
- reduces time for data delivery
- reduces resources (network, personnel, media, etc.)
l Steps:
- locate spatial, temporal, and spectral area of interest
- extract data
- re-assemble for distribution
The University of Alabama in Huntsville
UAH 8-10 September 1997
Design
� Web-based
� Dataset - independent
� HDF-EOS formatted data
� HDF-EOS software library
� Data types
� Swath
� Grid
The University of Alabama in Huntsville
UAH 8-10 September 1997
Functionality
�Back-end ( subsetter )
� C software using HDF-EOS and HDF libraries
executed in batch mode
criteria file (ODL)
�Front-end ( user interface )
� Forms-based Web application - obtains subsetting
selection criteria
The University of Alabama in Huntsville
UAH 8-10 September 1997
User Interface
� File selection
� Parameters/channels
� Geographic bounding box
� Time range
� Subsampling stride
� Non-geolocated objects
The University of Alabama in Huntsville
UAH 8-10 September 1997
Summary of Current
Functionality� Subsetter Functionality
� Can subset grid and swath data
� Files may contain multiple grids and/or swaths; user may select
any or all for subsetting
� Subset swath data on latitude/longitude and/or time
� Subset grid data on latitude/longitude
� Non-geolocated data may be included or excluded
� Output is HDF-EOS file using same data types
� “Back-end” runs as a batch job at archive center
� User may check status of job and/or cancel it
� E-mail sent to user when complete
� Data retrieved via FTP
The University of Alabama in Huntsville
UAH 8-10 September 1997
Restrictions
� Number of subsettable datasets limited by HDF-EOS library
subsetting functions:
� Latitude must be “Latitude” or “Colatitude”
� Longitude must be “Longitude”
� Latitude and longitude must be FLOAT32 or FLOAT64
� Latitude and longitude must be 1- or 2-dimensional
� Latitude and longitude must have identical dimensions
� Time must be “Time”
� Time must be FLOAT64 in TAI93 format
� Time must be 1- or 2-dimensional
� “Track” must be slowest varying dimension in geo fields
� Grid data must be in one of six supported projections
The University of Alabama in Huntsville
UAH 8-10 September 1997
Future Plans
� Relax requirements for latitude/longitude and time in
swath datasets
� Provide Java-based GUI for area-of-interest selection
� Allow user to apply one subset specification to multiple
input files
� Study integrating subsetter with a data visualization tool
� Study separating structural metadata from data
The University of Alabama in Huntsville
UAH 8-10 September 1997
What is Needed
� More test datasets in HDF-EOS format
� Additional support for modifications to HDF-EOS calls
� Accurate HDF-EOS documentation (internal and external)
� Functional Java map applet
� Resolution of metadata issues
� Publication of official metadata standards
� Name, content, and format of granule metadata
The University of Alabama in Huntsville
UAH 8-10 September 1997
Risks
� HDF-EOS not currently in widespread use
� HDF-EOS requirements for dataset-independent
subsetting not widely known to data producers
� Legacy datasets are not in HDF-EOS format
� Converting to HDF-EOS may increase storage
requirements
� Many datasets are on non-volatile media
The University of Alabama in Huntsville
UAH 8-10 September 1997
Summary
� A prototype Web-based dataset-independent subsetter has
been developed by UAH.
� Allows spatial, temporal, and spectral subsetting and
subsampling of HDF-EOS datasets
� Benefits science data users and data centers
� Great potential. but limited current use
Recommended