Exploring large marine datasets using an interactive

website and Google Earth

Jon Blower, Dan Bretherton, Keith Haines, Chunlei Liu, Adit Santokhee

Reading e-Science CentreEnvironmental Systems Science Centre

University of ReadingUnited Kingdom

Background• Marine science community uses

terabyte-scale datasets– numerical model output– satellite data

• Online data visualization is very useful

• Existing tools (e.g. LAS; first Godiva site, right) have many useful features but lack interactivity

• New Web technologies and geobrowsers can speed up exploration of large datasets– Can view data in context and at

range of spatial scales

The Web Map Service standard

• International standard for serving map images and metadata on the Web

• Supports different map projections• Directly supported by most GIS software, including

some geobrowsers (e.g. NASA WorldWind)

• We have developed a WMS for NetCDF data– Optimized for fast generation of map images on the fly

from source files– Open Source + available on web (ask me for details!)

• This is the basis for our interactive website

Architecture of our system

DATA WMS

Webserver

HTML,Javascript

Web server and WMScould be co-located

WMS = OGC-compliantWeb Map Service

metadata(XML)

images(PNG)

DATA WMS

Could useimages frommany otherWMSs

The Godiva2 website

Select a dataset and variable to display

http://lovejoy.nerc-essc.ac.uk:8080/ncWMS/godiva2.html

OSTIA sea surface temperature data

metadata loaded from

WMS and menus

populated

map image overlays

loaded from WMS

click and drag map

and use pan and zoom

controls

powered by OpenLayers

Zoomed in on Gulf Stream

Adjust colour range for

higher contrast

Gulf Stream 2: ocean eddies visible

set the transparency of the overlay

to view underlying

bathymetry

click the map to find the

actual data value at a

point (uses GetFeatureInfo in WMS spec)

Value: 292.4

Semi-transparent overlay

isotherms follow

bathymetry

Viewing in Google Earth• Godiva2 website contains

link to load currently-visible data in Google Earth– Our WMS outputs in KML

format• Can then view data

alongside other KML datasets

• No problem with map projections!– Although overlays still look

funny near the poles…• Can’t interact with the data

as much as is possible on the website

Large datasets in Google Earth• Some marine datasets are high-

resolution with global coverage• We want to be able to view these

datasets efficiently in GE– Cannot load whole dataset at full

resolution!• Solution: use a NetworkLink

– Reloads a new image from the WMS at an appropriate resolution every time the user moves the globe or zooms in/out

– GE automatically appends the bounding box (BBOX) of the visible area to the WMS query

• Works well, but is a little annoying for the user– Every small movement causes a

refresh

<kml><Folder>  <name>sea_water_temperature</name>   <description>Temperature of the Water

Column</description> <NetworkLink>  <visibility>1</visibility> <Url>  <href>http://…/WMS.py?

SERVICE=WMS&REQUEST=GetMap&VERSION=1.3.0&FORMAT=application/vnd.google-earth.kml+xml&LAYERS=amm/sst&ELEVATION=0&TIME=2006-12-03T00:00Z&WIDTH=500&HEIGHT=500</href>

  <refreshInterval>1</refreshInterval>   <viewRefreshMode>onStop</viewRefreshMode>   <viewRefreshTime>0</viewRefreshTime>   </Url>  </NetworkLink></Folder></kml>

What we would like to see in Google Earth

• Support for depth dimension– i.e. 3-D ocean bathymetry– Also for subsurface geological features

• Ability to add custom toolbars and behaviour– i.e. an API interface

• Direct support for Web Map Service standard– present (to some extent) in NASA WorldWind

Summary• We have built an interactive data visualization website from

open standards and open source software– "spreadsheet-style" interactivity– available for other groups to use– implemented as Java web app (WAR file)– we have extended WMS in some ways (but backward-compatible)

• Potential to overlay data from many different providers, for intercomparison

• Google Earth simple to use and good for display– but website gives much greater functionality and interactivity– New animation features in GE are a big plus for us

• We’d like to know more about other geobrowsers• See poster presentation and demo on Thursday

Plug for event next year!

• 2-day workshop on Google Earth and other internet mapping tools

• Focus on scientific applications for geobrowsers and geo-websites

• 2-3 April 2007, Cambridge, UK

• Presentations and coding tutorials

• Please email resc@rdg.ac.uk or see me if you are interested