An Overview of HDFEOS Part I

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An Overview ofHDF-EOS(Part I)

• Doug Ilg
• Raytheon STX
• Doug.Ilg_at_gsfc.nasa.gov
• [phone]

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Outline

• What is HDF-EOS?
• The Grid Interface
• The Point Interface

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What is HDF-EOS?

• An HDF Profile
• An extension to HDF
• A library built on top of HDF
• Three new data objects
• Three new programming interfaces

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Why HDF-EOS?
Standard HDF lacks well defined ways of handling
some key needs of EOSDIS

• Data structures for Earth remote sensing data and
  in-situ measurements with
• tightly coupled geolocation information
• subsetting services based on geolocation
• ECS metadata model

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HDF-EOS Platforms

• HDF-EOS Version 2.3 is available for
• Sun SPARC - Solaris
• SGI - IRIX
• DEC Alpha - Digital UNIX
• HP 9000 - HP-UX
• IBM RS/6000 - AIX
• PC - Windows 95/NT

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HDF-EOS Interfaces

• C and FORTRAN Interfaces for
• Grid Data (GD)
• Point Data (PT)
• Swath Data (SW)

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HDF-EOS Programming Model

• Writing
• open file
• create object
• define structure
• detach object
• attach object
• write data
• detach object
• close file

• Reading
• open file
• attach object
• inquire object
• read data
• detach object
• close file

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A Grid Data Set
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A Grid Structure
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Projections Supported

• Geographic
• Transverse Mercator
• Universal Transverse Mercator
• Hotine Oblique Mercator
• Space Oblique Mercator
• Polar Stereographic

• Lambert Azimuthal Equal Area
• Lambert Conformal Conic
• Polyconic
• Interrupted Goodes Homolosine
• Integerized Sinusoidal

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Components of the Grid Interface

• Access
• Definition
• Basic I/O
• Inquiry
• Subset
• Tiling

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Tips on Writing a Grid

• Order of calls is significant
• Setting a compression method affects all
  subsequently defined fields
• Setting a tiling scheme affects all subsequently
  defined fields

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Grid Subsetting Features

• By Geolocation
• GDdefboxregion/Gdextractboxregion
• By Vertical Field
• GDdefvrtregion/GDextractvrtregion
• By Time (special case of vertical)
• Tip use Geolocation, then Vertical/ Temporal

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Compression Methods for Grids

• Run-Length Encoding
• Adaptive Huffman
• Gzip

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A Point Data Set
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A Point Structure
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The Point Interface

• Access
• Definition
• Basic I/O
• Inquiry
• Subset

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Tips on Writing a Point

• Every level in a Point data set must be linked
  into the hierarchy.
• Before two levels can be linked, a link field
  must exist.

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Point Subsetting Features

• By Time
• PTdeftimeperiod/PTextractperiod
• By Geolocation
• PTdefboxregion/PTextractregion
• Tip use one or the other, not both

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Compression Methods for Points

• NONE

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Tips for HDF-EOS Coding

• Most operations (read, write, subset) work on a
  single field at a time.
• Region IDs and Period IDs are inter-changeable
  and can be reused to further reduce a subset.
• Partial writes (appending) on compressed fields
  are only supported through tiling.