April 21, 2023 © University of Reading 2008 www.reading.ac.uk

Reading e-Science CentreIntegrating a Web Map Service into the THREDDS Data ServerJon Blower, University of Reading, UKPauline Mak, University of Tasmania, AustraliaEthan Davis, John Caron, Unidata

Motivation• THREDDS is a very popular system for sharing environmental

data– Catalogue– Data access via OPeNDAP

• However, client-side tools are required for visualization– Not easy to use by people outside “our” community

• Web Map Service provides quick route to visualization– Produces georeferenced images– Images can be overlain to compare data– Very suitable for Web-GIS (low barrier to entry to users)

• Use of WMS mandated in Europe by INSPIRE directive– THREDDS already used by data providers

• WMS for NetCDF data already exists (http://ncwms.sf.net)– Both TDS and ncWMS are Java-based

• Hence we aim to integrate ncWMS with TDS

Web Map Service: a closer look

• GetCapabilities -> metadata

• GetMap -> map image, based on client-selected parameters, inc:– Image width/height– Image coordinate reference system– Geographic bounding box– Depth/height and time– Style

• GetFeatureInfo -> information about a particular map pixel– Format not standardized

• Specification supports 4D data– (Although tools often do not)

WMS Interoperability

NASA World Wind

Cadcorp SIS

Google Earth

3rd-party clients can’t use the custom WMS extensions

Why ncWMS?

• Based on same technology as TDS– Esp. Java NetCDF libraries

• Significant effort put into fast image generation

• Extensions to WMS to support scientific use cases– But fully backward-compatible with WMS specification

April 21, 2023 © University of Reading 2008 www.reading.ac.uk

Reading e-Science Centre

Scientific visualization using (nc)WMS

Notable features of ncWMS

• Fast generation of images

• Ability to read CF-NetCDF on variety of grids– inc. arbitrary grids and Murray tripolar

• Reproject images into large number of coordinate systems– E.g. polar stereographic

• Configuration via administrative web interface

Non-standard features• Piecemeal metadata-serving in JSON format

– avoids large XML Capabilities document

• Extra metadata for science data– e.g. units of measurement

• New parameters in GetMap for styling:– Choose colour palette– Set contrast range– Linear or logarithmic scaling– Far simpler than Styled Layer Descriptor

• Generation of timeseries plots via GetFeatureInfo

• … but fully backward-compatible with WMS1.1.1 and 1.3.0

Godiva2: a web client for ncWMS

• Interactively explore 4D geospatial raster datasets on the web

• ~40 datasets– Research data,

operational forecasts, satellite products

• Backed by ncWMS server

• OGC Website of the Month, January 2008

http://www.reading.ac.uk/godiva2

Selection of depth

Select from all the depth levels of the model

Selection of time (range)Select from all the timesteps in the model

Selection of a time range leads to an animation

Finding the data value at a point

Click on the data layer, data value and precise position is shown

Lon: -64.08 Lat: 36.21 Value: 19.27

Timeseries plots

If a time range is selected, can create a timeseries plot at a point

Vector plots

Selection of colour palette

Contrast-stretching

• Manual or automatic

Polar projections

Choice of background images

Export to Google Earth• Allows visualization of multiple

data sources

• Hurricane Katrina, August 2005

• Storm track positions (analysed from ECMWF vorticity data) by Lizzie Froude, ESSC

• Sea surface temperature data from UK Met Office FOAM model

• Combination shows cooling of surface waters on right-hand side of cyclonic storm track

• High winds cause upwelling of cool, deep water

Who’s using ncWMS/Godiva2?

• 100,000 GetMap requests served in 3 months– From 5 continents

• Customized versions of Godiva2 site set up for MERSEA and ECOOP projects– Major EU framework projects – INSPIRE compliance important!– Will be used in MyOcean

• UK National Centre for Ocean Forecasting

• Server software installed by:– Plymouth Marine Labs– AIMS, Australia– NOAA, US– USGS

• Code contributions from:– MeteoGalicia, Spain– TPAC, Tasmania– AIMS, Australia

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Reading e-Science Centre

Case study:European operational oceanography

Current architecture as used inMERSEA and ECOOP projects

OPeNDAP(THREDDS)

NetCDF

DataProvider 1 OPeNDAP

(THREDDS)

NetCDF

OPeNDAP(THREDDS)

NetCDF

WMS

Dynamic Quick ViewWeb portal(rebranded Godiva2)

Data providers already use TDS and OPeNDAP

Requires minimal setup

Single point of failure

Relies on fast, reliable OPeNDAP servers

DataProvider 2

DataProvider 3

Improved architecture:Anticipated MyOcean deployment

NetCDF NetCDF NetCDF

THREDDS

WMS

OPeNDAP

WCS?

THREDDS

WMS

OPeNDAP

WCS?

THREDDS

WMS

OPeNDAP

WCS?

WMS bundled with THREDDS

Data providers install single piece of software

Technical challenges

• Merging Spring-based code (ncWMS) with servlet-based code (TDS)– Spring is fairly non-intrusive so not too hard to decouple– TDS moving toward Spring architecture– Spring cleanly separates internal logic from presentation

• Merging catalogue and configuration systems– TDS system is more scalable

• Changes to underlying Java-NetCDF libraries– Upgrade from version 2.2 to version 4

• Aligning all of this with THREDDS-WCS– Single point of configuration for WMS and WCS metadata

Conclusions• First prototype of TDS-WMS now developed• To do:

– Testing (inc. scalability)– Tidying-up and refactoring– Integration of logging and usage monitoring– Integration of administrative web pages

• Anticipated immediate use in major European project MyOcean

• (By the way - version 4.0 of Java NetCDF libs appear significantly faster than version 2.2!)