Transcript Document

Exploring large marine
datasets using an interactive
website and Google Earth
Jon Blower, Dan Bretherton, Keith
Haines, Chunlei Liu, Adit Santokhee
Reading e-Science Centre
Environmental Systems Science Centre
University of Reading
United 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
WMS = OGC-compliant
Web Map Service
DATA
Web
server
WMS
metadata
(XML)
HTML,
Javascript
Web server and WMS
could be co-located
DATA
images
(PNG)
WMS
Could use
images from
many other
WMSs
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
click and
drag map
and use pan
and zoom
controls
map image
overlays
loaded from
WMS
powered by OpenLayers
Zoomed in on Gulf Stream
Adjust colour
range for
higher contrast
Gulf Stream 2: ocean eddies visible
click the map
to find the
actual data
value at a
point (uses
GetFeatureInfo
in WMS spec)
set the
transparency
of the overlay
to view
underlying
bathymetry
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 highresolution 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&REQ
UEST=GetMap&VERSION=1.3.0&FORMAT=a
pplication/vnd.googleearth.kml+xml&LAYERS=amm/sst&ELEVATI
ON=0&TIME=2006-1203T00:00Z&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