Development of a Prototype Web GIS Server for HDF-EOS Data based on OGC Web Map Specifications
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. Suresh
NASA/RITSS, 4500 Forbes Blvd, Lanham, MD 20706
NASA Goddard Space Flight Center, Code 423
Greenbelt, MD 20771, USA
• 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
Open GIS Consortium(OGC)
• A membership organization consisting of 220
members from GIS industries, government, and
• 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
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
– Extensive set of new specifications (details later)
– We are one of the OGC-paid participants
OGC Web Mapping Specification V1.0
• Define web interfaces for interoperability of map
assembly and delivery middleware within a
heterogeneous distributed computing environment
• Three interfaces for Web Mapping
• XML DTD for the capabilities description
• Tested in Phase I WMT.
• Web Map Server: provide interface for accepting multidimensional query requests and responding with
• Portrayal: provide interface for associating symbols with
• 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.
• Web Coverage Server: Provide interface for accepting multidimensional 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
• To develop a NASA Web GIS server
(NWGISS) that serves HDF-EOS data to
GIS clients according to OGC Web
– OGC Map Server, coverage server, and catalog
• The server should be able to serve data in
all three types of HDF-EOS data files.
• Easy-to-use and easy-to-setup.
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
• WMT II Specifications
– Web coverage server specifications
– Map server enhancements
• Web Catalog Server (Planned if funding available)
NWGISS Top Level Architecture
WMT GIS Clients
OGC Map Services
NWGISS OGC Server
Modified DIAL Data Server
Modified DIAL catalog server
• 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
• The server responses to the client request by
sending the XML capabilities file.
• Capabilities file contains information about
the server’s 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.
• 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
– 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.
• 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
client’s 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)
• 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.
• 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.
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
– WMT II is developing XML-based Image
Markup Language to encode metadata for raster
data and has external pointer to either HDFEOS or GeoTiff.
Coverage Server, Cont’d
• HDF-EOS Grid and Point
– Subset and subsampling data based on client’s
– 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.
Coverage Server, Cont’d
– Use the georeferencing information to determine the
maximum rectangle that covers the geographic bounding
box specified by the client and the box’s 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 bouding’s box’s 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.
Setup NWGISS at Your Machine
• If you have data in HDF-EOS, it is really
– Setup a web server if you don’t have
– Obtain NWGISS from us.
– Copy executables to cgi-bin directory of the
– Run CreateCapabilities program on your HDFEOS files to create a capabilities file.
– Register your server through OGC registry
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
– There are 19 servers in the testbed accessible
through the client, our one is called NASAEOSDIS