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Implementation of a Geospatial Imagery Digital Library using Java and CORBA

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Title: Implementation of a Geospatial Imagery Digital Library using Java and CORBA


1
Implementation of a Geospatial Imagery Digital
Library using Java and CORBA
  • Paul Coddington
  • Advanced Computational Systems Cooperative
    Research Centre
  • Computer Science Department, University of
    Adelaide
  • paulc_at_cs.adelaide.edu.au
  • TOOLS Asia 98
    September 1998

2
The Collaboration
  • On-Line Data Archives (OLDA) program of the
    Advanced Computational Systems (ACSys) CRC
  • Support for environment/agriculture GIS
    applications
  • Paul Coddington (DGIS project leader)
  • Ken Hawick (OLDA program leader)
  • Katrina Kerry, Jesudas Mathew, Andrew Silis,
    Darren Webb
  • Imagery Management and Dissemination (IMAD)
    project of the Defence Science and Technology
    Organisation (DSTO)
  • Support for defence and C3I applications
  • Paul Whitbread (IMAD project leader)
  • Mark Grigg, Colin Irving, Kim Tang, Rittwik Jana

3
On-line Data Archives
  • Many projects working on digital libraries, or
    on-line data archives, including OLDA project in
    ACSys CRC.
  • Aim to make data sets easily available via
    Internet.
  • Major advances in enabling technologies over past
    few years, with Web, CORBA, Java, faster
    networks.
  • Problems
  • Storing and serving data from large data archives
  • Finding the right data (querying and metadata
    standards)
  • Interoperability of data archives (interface
    standards)
  • On-demand processing of data (active data
    archives)
  • Downloading of data (large latencies, limited
    bandwidth)

4
Earth Observation Data Archives
  • We have been developing software to support
    online archives of earth observation system (EOS)
    data from satellites and aerial photography.
  • Want to provide easy access to online archives of
    EOS data from applet or application, potentially
    from multiple distributed interoperable data
    archives.
  • Archive management software must support
    ingesting and storing of data, and provide
    interfaces for searching, browsing, processing
    and downloading of large image data files.
  • Should be robust, efficient, interoperable, with
    standard interfaces and access mechanisms (where
    available).

5
Applications of EOS Data Archives
  • EOS data is used for many applications - mining,
    agriculture, environmental studies, defence, etc.
  • Remote sensing is particularly important for a
    large, sparsely populated country like Australia.
  • Applications we are supporting include
  • Spotting bushfires in remote areas
  • Crop yield prediction
  • Studies of correlation between rainfall and
    vegetation growth
  • Localised rainfall and frost predictions
  • Defence C3I

6
EOS Archives
  • Many EOS data archives have been made available
    online over past few years, e.g.
  • NASA EOS Data and Information System
  • ACRES Digital Catalog
  • Caltech/JPL Synthetic Aperture Radar Atlas (SARA)
  • We have created an archive of GMS-5 geostationary
    meteorological satellite data for software
    demonstrators and prototypes, and to support some
    applications.
  • Major effort in U.S. to develop national spatial
    data infrastructure for federal agencies and
    defence.
  • Key issue is interoperability and standardisation
    of interfaces and metadata -- lots of effort in
    this area.

7
Interface Standards
  • Currently lots of work on developing standards
    for interfaces (particularly O-O interfaces) to
    online data archives, particularly for geospatial
    data.
  • Driven primarily by U.S. federal and defence
    agencies, such as National Imagery and Mapping
    Agency (NIMA), but now also Open GIS Consortium
    (OGC) and ISO.
  • NIMA is developing U.S. Imagery and Geospatial
    Services (USIGS) specification.
  • USIGS specifies an object-oriented system with
    interfaces specified in using IDL.
  • Done in collaboration with OMG, targeted at CORBA
    implementations.

8
USIGS
  • USIGS is made up of a number of parts, including
  • Geospatial and Imagery Access Services (GIAS)
    specification, for interfacing to image libraries
  • USIGS Common Object Specification (UCOS), giving
    detailed specifications of objects that are
    common to different parts of USIGS
  • USIGS Interoperability Profile (UIP), specifying
    common interfaces and data models for
    interoperability between different parts of USIGS
  • Specification of standards for metadata and data
    models
  • National Imagery Transfer Format Standard
    (NITFS), a standard image file format for
    interoperability
  • GIAS and UCOS have an IDL interface specification.

9
Geospatial Imagery Access Services
  • GIAS is structured so that the main functions of
    the library, such as adding, querying and
    accessing data, and controlled by different
    managers.
  • Library class handles access and authentication.
  • Catalog Access Manager handles queries.
  • Creation Manager handles ingest of data and
    metadata.
  • Data Model Manager handles logical data model.
  • Order Manager (or GeoDataSetMgr) handles
    dissemination of image data as files.
  • Array Access Manager handles dissemination of
    images as pixel arrays direct to client
    application.

10
GIAS Implementation
  • We have focussed on developing an implementation
    of the main part of USIGS, the GIAS-compliant
    image server.
  • Implemented using Java for both client and server
    code (current version uses JDK 1.1.5), wanted
    server code to be portable, and to fit in with
    development of middleware system (DISCWorld)
    which is developed in Java.
  • Client can be applet or application.
  • Client/server interface done using CORBA
    (required for integration with defence system).
  • Started development using OrbixWeb but moved to
    Visibroker - more convenient for running on our
    SGI server, also supported by Netscape.

11
Image Database Implementation
  • Attempted to save development effort by using
    commercial off-the-shelf system for image
    database.
  • StudioCentral from Silicon Graphics provides a
    C class library for building a digital
    multimedia asset management system, targeted
    mainly at film-making industry but appeared
    well-suited to general image data archive.
  • All image access and querying goes through
    StudioCentral API, classes called as native
    methods from Java.
  • Implementation of CORBA lt-gt Java lt-gt
    StudioCentral was more difficult than expected.
  • We have also developed a portable JDBC
    implementation, which was probably easier to
    implement.

12
Query Language
  • GIAS and StudioCentral adopt the approach of
    using a higher-level query language that SQL, in
    order to abstract over details of the data model,
    which may change or may not be known by the
    client.
  • GIAS uses Boolean Query Syntax (BQS), which has
    some support for querying on regions (not
    available in StudioCentral query language).
  • We have developed a parser to convert BQS queries
    to StudioCentral query language and to SQL (for
    JDBC version).
  • Standards for object relational databases and
    query languages are still under development.

13
Image Repository Architecture
14
Test Client Interface
15
Implementation Problems
  • Write-once, run anywhere not true yet for
    Java. compatibility problems with different
    versions of JDK and different JVMs.
  • CORBA is worse - ORBs do not implement all parts
    of the specification, different implementations
    support different parts of the spec and may not
    be interoperable.
  • Hard to integrate Java and CORBA within IDL
    constraints.
  • Interfacing to C class libraries is not easy
    with current Java Native Interface (JNI), but
    much better in JDK 1.2.
  • Many applications, such as StudioCentral, do not
    provide support for Java and CORBA interfaces,
    but this is changing as software becomes Java and
    CORBA aware.

16
Future Work
  • Currently developing Java RMI version of
    interface.
  • Quantitative performance evaluations and
    comparisons of different implementations (RMI,
    CORBA, JDBC, different databases, etc)
  • Porting and developing applications to use
    standard interface.
  • Continue revising our implementation to track
    evolving standards, from GIAS, Open GIS
    Consortium and ISO (they will hopefully
    converge).
  • Keep up with new versions of JDK, ORBs, etc.
  • Provide more support for active data archives.
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