MapServer Web Coverage Server by huanglianjiang1


									MapServer Support for Web
   Coverage Services
      Stephen Lime - Minnesota DNR
Dr. Thomas E. Burk - University of Minnesota

       MUM 2004 - Ottawa, Canada
    Presentation Overview
•   Background
•   Implementation
•   Usage
•   Demo Application
•   Future Work
• Pre-dates OGC interoperability efforts
• Two primary objectives, via the Internet:
     o create maps and associated products (e.g., scalebars,
       legends and reference maps)
     o query spatial data

• Two primary components:
     o   mapserv CGI provides out-of-box functionality
     o   MapScript, access to the C/C++ API from popular
         programming languages
• Geographic Data Abstraction Library
• Middleware for raster data access, similar in
  concept to ODBC
• Provides most MapServer raster input and
  some output capabilities
• Provides limited image processing support
  for operations such as projection and
MapServer OGC Support
• Web Mapping Service (WMS) - a perfect match
  for existing MapServer functionality
• Web Feature Service (WFS) - MapServer supports
  non-transactional elements, equates roughly to
  MapServer query support
• Web Coverage Service (WCS) - furthest spec
  from core MapServer functionality, must rely
  heavily on MapServer/GDAL interface
• MODIS Download Facility – early 2000
   Firstextension of MapServer that has several
    characteristics of recent WCS standard
• Lead to development of a SEEDS proposal
  for NASA funding
   Partners:University of North Dakota and the
    Jet Propulsion Laboratory
 WCS Overview
• Like WFS, WCS is a natural progression from
• “Unfiltered” access to a “coverage”, values or
  properties at a set of geographic locations
• WCS 1.0.0 is limited to simple, that is grid,
  coverages *whew*
• Supports simple queries in the form of spatial,
  temporal and/or other property subsets
  Design Assumptions
• Not a ground-up WCS implementation
     Will not support the full WCS specification
     Build upon functionality already available within MapServer
     Any extensions to MapServer must be made available via the
      core product, the CGI interface and MapScript
     Must integrate with OGC specification implementations
      supported by MapServer (e.g. WMS and WFS)
     Relies upon GDAL for data extraction, transformation (e.g.
      projection) and formatting
Our “ToDo” List
• Enable ISO8601 extended date format parsing
• Enhance tiling to support:
      o   filtering based on tile attributes
      o   specification of band/bands as an attribute
• Alter GDAL/MapServer interface to support key
  WCS features (multi-band raw mode)
• Update MapServer compilation process
• Developed interface to process WCS requests via
  the MapServer CGI program
      o   GetCapabilities/DescribeCoverage/GetCoverage
  Spatial/Temporal Tiling
• Mechanism to organize and present a large
  volume of data using a single MapServer
  layer definition
• Has utility beyond immediate WCS needs, for
  example for access control
• Simplifies development of client applications
• Potential performance benefits
• May be cumbersome to setup
Tiling Example: Multiple Images
                           shape    location

                          polygon    1.img

                          polygon    2.img
  1.img   2.img   3.img
                          polygon    3.img

                          polygon    4.img
  4.img   5.img   6.img
                          polygon    5.img

                          polygon    6.img

  7.img   8.img   9.img   polygon    7.img

                          polygon    8.img

                          polygon    9.img
Tiling Example: Single
Image, Temporal Bands
 NDVI_03.img    shape    band    date       location

               polygon    1     2003-05   NDVI_03.img

    May        polygon    2     2003-06   NDVI_03.img

    June       polygon    3     2003-07   NDVI_03.img

    July       polygon    4     2003-08   NDVI_03.img

 Development Status
• Elements of WCS (e.g. tiling) is enabled in
  4.2 release, beta WCS support is now
  available in 4.3 development version
• Requires GDAL and Proj.4
• Supports GetCapabilities,
  DescribeCoverage and GetCoverage
 Enabling WCS
• Very similar to enabling WMS and WFS
• Define WCS specific metadata elements
      GDAL can discover some values (e.g. resolution)
      Optionally, these values can be hardcoded
• Set the layer DUMP attribute
• If necessary, structure image data appropriately
  using new tiling capabilities
  NAME "ndvi"                          An Example
    wcs_label "North Central US MODIS-based NDVI Images for 2002"
    ows_srs "EPSG:26915 EPSG:4269 EPSG:4326"
    ows_extent "159707 4597895 1400207 5501395"
    wcs_resolution "500.0 500.0"
    wcs_formats "GEOTIFF_INT16"
    wcs_nativeformat "raw binary"
    wcs_timeposition "2002-001,2002-033,…,2002-193"
    wcs_timeitem "imgdate"
  END                                                LAYER
  DUMP TRUE                                             NAME "ndvi_idx"
  TILEINDEX 'ndvi_idx'                                  TYPE TILEINDEX
END                                                     DATA "mod13"
 Demo Application
• MODIS Download Facility
• Run the demo...
    Future Enhancements
• Non-temporal range subsetting
       Via TILEINDEX layers
       Via raster cell values
•   Automatic metadata discovery
•   XML encoded requests
•   Support for multiple spatial interpolation methods
•   True support of ISO8601 date formats
•   WCS client support
•   Oh yeah, need to write documentation

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