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

MapServer Support for Web Coverage Services

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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 - PowerPoint PPT Presentation

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Page 1: MapServer Support for Web Coverage Services

MapServer Support for Web Coverage Services

Stephen Lime - Minnesota DNRDr. Thomas E. Burk - University of Minnesota

MUM 2004 - Ottawa, Canada

Page 2: MapServer Support for Web Coverage Services

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

Page 3: MapServer Support for Web Coverage Services

MapServer• 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 functionalityo MapScript, access to the C/C++ API from popular

programming languages

Page 4: MapServer Support for Web Coverage Services

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

Page 5: MapServer Support for Web Coverage Services

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

Page 6: MapServer Support for Web Coverage Services

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

Page 7: MapServer Support for Web Coverage Services

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

Page 8: MapServer Support for Web Coverage Services

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

Page 9: MapServer Support for Web Coverage Services

Our “ToDo” List• Enable ISO8601 extended date format parsing• Enhance tiling to support:

o filtering based on tile attributeso 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 programo GetCapabilities/DescribeCoverage/GetCoverage

Page 10: MapServer Support for Web Coverage Services

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

Page 11: MapServer Support for Web Coverage Services

Tiling Example: Multiple Images

1.img 2.img 3.img

4.img 5.img 6.img

7.img 8.img 9.img

shape location

polygon 1.img

polygon 2.img

polygon 3.img

polygon 4.img

polygon 5.img

polygon 6.img

polygon 7.img

polygon 8.img

polygon 9.img

Page 12: MapServer Support for Web Coverage Services

Tiling Example: Single Image, Temporal Bands

August

July

June

May

NDVI_03.img shape band date location

polygon 1 2003-05 NDVI_03.img

polygon 2 2003-06 NDVI_03.img

polygon 3 2003-07 NDVI_03.img

polygon 4 2003-08 NDVI_03.img

Page 13: MapServer Support for Web Coverage Services

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

Page 14: MapServer Support for Web Coverage Services

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

Page 15: MapServer Support for Web Coverage Services

An Example

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

LAYER NAME "ndvi_idx" TYPE TILEINDEX DATA "mod13"END

Page 16: MapServer Support for Web Coverage Services

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

Page 17: MapServer Support for Web Coverage Services

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

Page 18: MapServer Support for Web Coverage Services

Questions?