HDF5 OPeNDAP ProjectUpdate and Demo

MuQun Yang and Hyo-Kyung Lee (The HDF Group)

James Gallagher (OPeNDAP, Inc.)

OPeNDAP Review

• A software framework that allows simple access to remote data

• Data Access Protocol• Client-server model• Widely used by Earth Science Community

Example Usage

OPeNDAP Client

OPeNDAPHDF4 Server

HDF4

Syntactic Structure of DataSemantic Meaning of Data

Actual Content of Data

OPeNDAP Visualization Client

Why Important?

• HDF5: NASA EOS / NPOESS

• NASA’s MISSION: ACCESS!

• Our MISSION: Build a DAP-HDF5 Bridge

OPeNDAP HDF5 Server

1. Map HDF5 Datatypes into DAP Datatypes

2. Plus, tweaks for OPeNDAP Clients

3. Plus, tweaks for HDF-EOS Files

Goal: Access HDF5 data via OPeNDAP

Mapping HDF5 Datatypes• Prototype server in 2001

• NASA Grant from Nov. 2006

• Support for Compound Datatype

• Support for Group

• Support for References / Links

• First Product Release in Mar. 2008

OPeNDAP HDF5 Server

1. Map HDF5 Datatypes in DAP Datatypes

2. Plus, tweaks for OPeNDAP Clients

3. Plus, tweaks for HDF-EOS Files

Goal: Access HDF5 data via OPeNDAP

OPeNDAP Clients

• I hate long variable names.

• I need special attributes on dataset.

• I care only Grid datatypes.

• I care only well-formed attributes.

Not all OPeNDAP clients are created equal!

Tweaks for OPeNDAP Clients Two configuration options

• --enable-short-name

• --enable-CF

OPeNDAP HDF5 Server

1. Map HDF5 Datatypes in DAP-way

2. Plus, tweaks for OPeNDAP Clients

3. Plus, tweaks for HDF-EOS5 Files

Goal: Transform HDF5 access in DAP-way

HDF EOS

• Grid with No Dimension data Clients expect Grid with Dimension data

• Some Attributes stored in Extremely Long String(s) (e.g. StructMetada.0) Clients expect well-structured attributes

Not all HDF5 files are created for DAP!

Tweaks for HDF-EOS Two more configuration options

• --enable-eos-grid

• --enable-eos-meta

Day After Server Tweaks

• Finally, Happy Clients!

GrADSNCLFerretMATLAB

ncBrowse

IDVODC

IDL

Goals

•1st : Access HDF5 via OPeNDAP

• 2nd: Construct HDF5 data from OPeNDAP Bonus: Help clients to better access EOS

Swath data

Some Things

• Hard: Opaque, Bitmap, Enum, Variable Length types

• Illegal: Reserved characters in DAP are used in Dataset/Group name in HDF5

(that OPeNDAP HDF5 server can’t serve)

For Everything Else

• Let there be HDF5-Friendly OPeNDAP client library!

• Package and Deliver in DAP first.

• Then, let the client library handle it.

Example: Group in HDF5Traditional OPeNDAP client library: It’s an attribute that I don’t understand. I’ll ignore it.

HDF5-Friendly OPeNDAP client library: I was waiting for this key attribute to re-construct HDF5

Example: Reference in HDF5

• Object / Regional Reference

• Map to DAP URL

• Important for NPOESS

• One more reason: Help Clients to view Swath

• Only ODC can display Swath properly.

HDF5-Friendly OPeNDAP Client Library

• Easy but Rigid OPeNDAP NC Client Library! easy: same as netCDF C interface rigid: follows netCDF model

• Our client library must be Easy but Flexible

No Latitude and Longitude

Courtesy of NASA

libnc-dap

???

liboc-dap

NC-Friendly OPeNDAP Client Library

libdap

dapserver

OPeNDAP NC Server

GrADS

NetCDFView NetCDFHDF5

Group/Ref/Swath

OPeNDAP HDF5 Server

View HDF5

GrADS

View G/R/Swath

HDF5-Friendly OPeNDAP Client Library

Example: dap2h5

• A test application for the client library

• It can construct HDF5 from DAP output

ORIGINAL

CONSTRUCTED

Demo: GrADS

• GrADS is modified to use our library

• The client library provides grid mapping

from swath data

• GrADS displays swath through HDF-EOS5

specific client library API calls

Caution

• Our Client Library is ONLY PROTOTYPE! It does NOT support all DAP data types

It does NOT support all AURA files It does NOT support all Visualization clients

Summary

• HDF5 Access via OPeNDAP Is Easy / Efficient / Cool Loses some things Requires HDF5-friendly OPeNDAP Client Library

• HDF5-Friendly OPeNDAP Client Library Prototype Serves HDF5 better(EOS swath) Benefits visualization clients

Future Work• HDF5 to DAP2 Mapping Document

• Release HDF5-friendly OPeNDAP Client Library Prototype

• URL: http://hdfgroup.org/projects/opendap/index.html

Credits

Mike Folk (THG)Robert McGrath (NCSA)

Peter Leonard, Daniel Kahn, Marghi Hopkins (ADNET)Christopher Lynnes, James Johnson, Denis Nadeau, Fan Fang (NASA)

Jennifer Adams (GrADS)Dave Brown (UCAR)

Acknowledgement

This work was supported basing upon the Cooperative Agreement with the National Aeronautics and Space Administration (NASA) under NASA grant NNX06AC83A and NNX06AG75A. .  Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of NASA.