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MapServer Support for Web Coverage Services

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. MapServer. Pre-dates OGC interoperability efforts

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MapServer Support for Web Coverage Services

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  1. MapServer Support for Web Coverage Services Stephen Lime - Minnesota DNR Dr. Thomas E. Burk - University of Minnesota MUM 2004 - Ottawa, Canada

  2. Presentation Overview • Background • Implementation • Usage • Demo Application • Future Work

  3. MapServer • Pre-dates OGC interoperability efforts • Two primary objectives, via the Internet: • create maps and associated products (e.g., scalebars, legends and reference maps) • query spatial data • Two primary components: • mapserv CGI provides out-of-box functionality • MapScript, access to the C/C++ API from popular programming languages

  4. GDAL • 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 resampling

  5. 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

  6. Groundwork • MODIS Download Facility – early 2000 • First extension 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

  7. WCS Overview • Like WFS, WCS is a natural progression from WMS • “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

  8. 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

  9. Our “ToDo” List • Enable ISO8601 extended date format parsing • Enhance tiling to support: • filtering based on tile attributes • 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 • GetCapabilities/DescribeCoverage/GetCoverage

  10. 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

  11. Tiling Example: Multiple Images 1.img 2.img 3.img 4.img 5.img 6.img 7.img 8.img 9.img

  12. Tiling Example: Single Image, Temporal Bands NDVI_03.img May June July August

  13. 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

  14. 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

  15. LAYER NAME "ndvi" STATUS OFF TYPE RASTER METADATA 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 DUMP TRUE TILEINDEX 'ndvi_idx' END An Example LAYER NAME "ndvi_idx" TYPE TILEINDEX DATA "mod13" END

  16. Demo Application • MODIS Download Facility • Run the demo...

  17. 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

  18. Questions?

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