Development of a Prototype Web GIS Server for HDF-EOS Data based on OGC Web Map Specifications

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Development of a Prototype Web GIS Server for
HDF-EOS Data based on OGC Web Map Specifications

• Liping Di, Zhangshi Yin, Wenli Yang, Meixia Deng,
  and R. SureshNASA/RITSS, 4500 Forbes Blvd,
  Lanham, MD 20706lpd_at_rattler.gsfc.nasa.gov
• Ken McDonaldNASA Goddard Space Flight Center,
  Code 423Greenbelt, MD 20771, USA

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Introduction

• HDF-EOS is the standard data format for NASA
  EOSDIS. Huge amount of remote sensing data will
  be produced in this format.
• Make HDF-EOS data easily accessible to GIS users
  will greatly increase the utilization of EOSDIS
  data.
• There are three data models in HDF-EOS
• Grid--Georectified raster data
• Swath--potential georeferable raster data
• Point-- point measurement

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Open GIS Consortium(OGC)

• A membership organization consisting of 220
  members from GIS industries, government, and
  universities.
• Promotion of the interoperability of GIS systems,
  data, and services in the network environment.
• The main work of OGC is to develop interface
  specifications for GIS interoperability though
• Regular standard development procedure
• Testbed activities

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Web Mapping Testbed(WMT)

• Phase I (WMT I)
• Finished in September 1999 and produced
• Web Mapping Specification Version 1.0
• A set of prototype interoperable clients,
  middleware, and servers developed by
  participating members.
• Phase II (WMT II)
• Started in July 2000, and will finish by the end
  of this year.
• Extensive set of new specifications (details
  later)
• We are one of the OGC-paid participants

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OGC Web Mapping Specification V1.0

• Define web interfaces for interoperability of map
  assembly and delivery middleware within a
  heterogeneous distributed computing environment
  over Internet.
• Three interfaces for Web Mapping
• GetMap
• GetCapbilities
• GetFeatureInfo
• XML DTD for the capabilities description
• Tested in Phase I WMT.

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WMT-2

• Web Map Server provide interface for accepting
  multi-dimensional query requests and responding
  with symbolized graphics
• Portrayal provide interface for associating
  symbols with geographic feature.
• General service model provide interface for
  representing service metadata, service
  capabilities, and service interfaces using XML.
• Web Feature Server, Filter, ID Provide interface
  for accepting spatially enabled SQL-like query
  request and responding with GML feature
  collections, include spatially enabled filter
  grammar.

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WMT-2, Contd

• Web Coverage Server Provide interface for
  accepting multi-dimensional query requests and
  responding with real, gridded data (OGC
  coverages)
• Geography Markup Language (GML) Provide XML
  encoding for geographic features, including XML
  schema definition to structure encodings and
  temporal extensions.
• Imagery and Coverage Markup Language Provide XML
  encoding for images, gridded data, and textual
  and graphical annotation on extensions.
• Security and E-Commerce Demonstrate application
  of commercial security technologies.
• OGC catalog server test the catalog
  specification in WMT 2.

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Objectives

• To develop a NASA Web GIS server (NWGISS) that
  serves HDF-EOS data to GIS clients according to
  OGC Web Mapping Specifications.
• OGC Map Server, coverage server, and catalog
  server
• The server should be able to serve data in all
  three types of HDF-EOS data files.
• Easy-to-use and easy-to-setup.

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OGC Web Mapping Interfaces To Be Implemented in
NWGISS

• Meet WMS version 1.0 for all HDF-EOS 3 data
  models in the map server
• GetCapabilities
• GetMap
• GetFeatureInfo
• WMT II Specifications
• Web coverage server specifications
• Map server enhancements
• Web Catalog Server (Planned if funding available)

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NWGISS Top Level Architecture
WMT GIS Clients
OGC Map Services
NWGISS OGC Server
Map/Coverage/Feature
Catalog
Capabilities
Modified DIAL Data Server
Modified DIAL catalog server
data access
catalog access
XML capability files
CreateCapabilities
HDF-EOS Files
Data Catalog
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Current Status

• All three interfaces of the map server are
  implemented, tested through WMT I, and will be
  released to users by the end of September.
• Free to NASA customers.
• An alpha version of the coverage server is
  developed and released to WMT II for testing.
• Plan to release the coverage server with map
  server enhancement by end of the year

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GetCapabilities

• The server responses to the client request by
  sending the XML capabilities file.
• Capabilities file contains information about the
  servers capabilities as well as data served by
  the server (catalog).
• CreateCapabilities reads HDF-EOS structure
  information, converts it to layer structure, and
  encode it in XML.

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GetMap

• The server sends a map back to the client in the
  exact geographic area, size, projection, style,
  and encoding specified by the client.
• HDF-EOS grid
• Subset the grid by the geographic area specified
  by the client.
• Resampling the subset grid to the specified size.
• Convert data to 8-bit image with specified style
  and encode it with specified encoding (e.g. gif)
• No reprojection is done at NWGISS but a cascading
  server in WMT I can do the job.

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GetMap, Contd

• HDF-EOS Swath
• Not georectified but OGC map server requires data
  to be georectified (e.g., the HDF-EOS grid).
• Geo-rectify swath data on-the-fly based on the
  clients specifications and georeferencing
  information associated with a swath.
• This step performs both subsetting and
  resampling.
• Convert data to 8-bit image based on style
  required by the client
• Encode the image (e.g. gif)

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GetMap, Contd

• HDF-EOS Point
• Subset the point data based on the geographic
  area specified by the client.
• Rasterize the point data by plotting the point on
  8-bit raster with the style specified by the
  client.
• Encode the 8-bit raster map.

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GetFeatureInfo

• The server returns to client the information
  about a geographic location specified by the
  geographic coordinate from the client.
• NWGISS returns the real data values encoded in
  XML for the coordinate.

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NWGISS Coverage Server

• Coverage server returns the real data and
  associated information to the client with client
  specified geographic location, parameters, and
  encoding.
• Current specification selected HDF-EOS, GeoTiff,
  GML (for vector data) as the encoding method.
• WMT II is developing XML-based Image Markup
  Language to encode metadata for raster data and
  has external pointer to either HDF-EOS or GeoTiff.

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Coverage Server, Contd

• HDF-EOS Grid and Point
• Subset and subsampling data based on clients
  specifications.
• Repack the subset data in HDF-EOS.
• Copy the original core metadata with a note of
  the subsetting--too difficult to change coremeta.
• Multi-dimensional subsetting for grid
• No reprojection is implemented yet.

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Coverage Server, Contd

• Swath
• Use the georeferencing information to determine
  the maximum rectangle that covers the geographic
  bounding box specified by the client and the
  boxs projection in the swath coordinate, which
  usually are not a rectangle.
• Retrieve the swath scanlines, truncate the
  scanlines by the maximum rectangle, fill the
  fill-value between the maxium rectangle and the
  boudings boxs projection.
• Package the subset data in HDF-EOS with the
  geolocation info for the data from the original
  file.
• Plan to provide georectified data as an option in
  the future.

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Setup NWGISS at Your Machine

• If you have data in HDF-EOS, it is really easy
• Setup a web server if you dont have
• Obtain NWGISS from us.
• Copy executables to cgi-bin directory of the web
  server.
• Run CreateCapabilities program on your HDF-EOS
  files to create a capabilities file.
• Register your server through OGC registry
• Done.

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NWGISS Map Server Demo

• A demo map server has been setup.
• With sample MODIS level 1b, TOMS ozone, etc, and
  more data will be added.
• Part of WMT I testbed, accessible through
  Cubewerx client. http//209.217.120.146/wmt/cubevi
  ew/cubeview.cgi
• There are 19 servers in the testbed accessible
  through the client, our one is called NASA-EOSDIS

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