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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 lpd@rattler.gsfc.nasa.gov

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

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  1. 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@rattler.gsfc.nasa.gov Ken McDonaldNASA Goddard Space Flight Center, Code 423Greenbelt, MD 20771, USA

  2. 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

  3. 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

  4. 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

  5. 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.

  6. 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.

  7. WMT-2, Cont’d • 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.

  8. 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.

  9. 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)

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

  11. 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

  12. GetCapabilities • 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.

  13. 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.

  14. GetMap, Cont’d • 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)

  15. GetMap, Cont’d • 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.

  16. 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.

  17. 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.

  18. Coverage Server, Cont’d • HDF-EOS Grid and Point • Subset and subsampling data based on client’s 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.

  19. Coverage Server, Cont’d • Swath • 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.

  20. Setup NWGISS at Your Machine • If you have data in HDF-EOS, it is really easy: • Setup a web server if you don’t 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.

  21. 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/cubeview/cubeview.cgi • There are 19 servers in the testbed accessible through the client, our one is called NASA-EOSDIS

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