Exploring large marine datasets using an interactive website and Google Earth Jon Blower, Dan...
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Transcript of Exploring large marine datasets using an interactive website and Google Earth Jon Blower, Dan...
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 [email protected] or see me if you are interested