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• 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

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

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

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

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

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 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

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

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

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

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

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

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

Questions?