Transcript SeaGrid_FOSS4G

Managing WMS and WCS on
multidimensional NetCDF Datasets with
Geoserver
•Martin Desruisseaux, Geomatys
•Mickael Treguer, Ifremer
Ifremer
 National institute of marine research, the French public institute for marine
research, Ifremer contributes, through studies and expert assessments, to
knowledge about the ocean and its resources, monitoring of marine and
coastal zones and the sustainable development of maritime activities.
To these ends, it designs and operates observational, experimental and
monitoring tools and facilities. Ifremer manages the ocean research fleet for
the French scientific community.
Fisheries and aquaculture Ocean floors
Ocean physics
Example of gridded datasets
 Physical Oceonography
• Temperature and Salinity
• Sea Surface Temperature
• Current
• Wave
• …
 Biological Oceanography
• Ocean color (chlorophyll)
 Digital Elevation Model (DEM)
 …
NetCDF (Common Data Form)
 Binary format suitable for lots of different data types
• portable self-describing binary data format.
• NetCDF is used extensively in the atmospheric and oceanic
science communities.
 Climate and Forecast conventions should be applied to environmental
data if possible
• for correct labelling of axes (latitude, longitude, time, pressure,
etc)
• for standard naming of variables
(sea_water_potential_temperature etc)
 Can also be dissiminated via the protocol OPeNDAP
• you access data using a URL
 Allow GIS clients to access NetCDF/OPeNDAP datasets via
standards-based interface (WMS, WCS)
4-D web mapping
 A number of mapping systems are now available on
the web
• Most mapping software assumes twodimensional data (x-y)
 Environmental science data is dynamic and fourdimensional (x-y-z-t)
 OGC WMS/WCS support 4(plus)-D data (elevation,
time)
• But not many servers or clients support the full
specification
OGC NetCDF architecture
Client Application
(Mapbuilder)
GeoServer / GeoTools
WMS
WCS
NetCDF Interface
(Unidata)
OpenDAP
netCDF
files
SeaGrid
•“SeaGrid”
website provides
very quick
visualisations of
gridded data
•Images
generated
dynamically on
the server
Selection of depth
depth levels
available on
the data
<Layer queryable="1">
<Name>geom:coriolis</Name>
...
<Dimension name="elevation" units="EPSG:5030"/>
<Extent name="elevation" default="5">5,10,20, ... ,1850,1900,1950</Extent>
...
</Layer>
Selection of time
time available
on the data
animation
<Layer queryable="1">
<Name>geom:coriolis</Name>
...
<Dimension name="time" units="ISO8601"/>
<Extent name="time" default=" 2007-06-20T14:00:00Z ">2007-0606T14:00:00Z,2007-06-13T14:00:00Z,2007-06-20T14:00:00Z</Extent>
...
</Layer>
WCS
Draw a bbox
to extract
raw raster
data
GetCoverage
WCS
specification
Future enhancements
 It is planned to improve :
• Extraction WCS
– Official supported format : GeoTiff, HDF-EOS, DTED,
NITF, GML
– Add Netcdf output (convention CF)
 It is planned to provide :
•Access to opendap (distributed
datasets)
•WMS GetFeatureInfo to retreive
geophysical data
•Display wind/current fields as
vectors (directions and intensities)
Past work
 In GeoTools
– Wrote initial referencing module
– Wrote initial coverage module
• Strong focus on geophysics data
• Some processing capabilities
• No raster input/output
 On SourceForge
–
–
–
–
Created SeaGIS in 2002
Raster input/output performed there, requiring database
Initially designed for a specific problematic (fisheries...)
Running since 2002, trying to generalize since that time
Topics
 PostGrid as a coverage catalog
 Geographic Image I/O
Coverage catalog
 « PostGrid » is a schema in a PostGIS database
 Contains coverage metadata, not pixel values
 Used as an index for fast coverage lookup
– Which data are available (what, where, when…)
– How to get the data (filename, format…)
– What the pixel values means (categories…)
Images stay files in their native format (NetCDF, PNG…)
Current PostGrid scope
 Envelope up to 4 dimensions (x,y,z,t)
– Mandatory horizontal (x,y)
• The SRID must be supported by PostGIS
• The « grid to CRS » transform must be affine
– Optional vertical (z)
• SRID must be provided, but doesn't need to be supported
• Ordinates as an array of values
– Optional temporal (t)
• Set of time ranges
Horizontal slices in arbitrary files for different (z,t)
Current PostGrid scope
 Envelope up to 4 dimensions (x,y,z,t)
– Mandatory horizontal (x,y)
• The SRID must be supported by PostGIS
• The « grid to CRS » transform must be affine
Affine transform versus envelope
 Can compute one from the other...
• grid range
• affine transform
• envelope
• coordinate reference system
... but envelopes are
ambiguous!
– Do we reverse y axis direction?
– Do we swap axes (x,y) → (y,x)?
– What about oblique grids?
Always specify Transform rather than Envelope when
possible
...but envelopes are still valuable for indexing!
Database schema overview
Series
∞
1
• identifier
• layer
• path
• format
∞
GridCoverage
s
• series
• filename
• startTime
• endTime
• extent
∞
1
GridGeometries
• identifier
• width, height
• scaleX, scaleY, ...
• horizontalSRID
• horizontalExtent
• verticalSRID
• verticalOrdinates
• An indexed geometry column
• Always in WGS84 (not image CRS)
• Automatically generated by trigger
1
Formats
1
∞
SampleDimensions
1
∞
Categories
Categories




Tell what the pixel values means
Convert to and from geophysics values
They are not styling
Required even if the data are already geophysics
– Relationship to pixel values is typically fixed for a data set
– What this NaN value is? (clouds, land...)
↔ Geophysics values
Pixel values
0
1
2
3 .. 255
=
=
=
=
no data
clouds
land
temperature
↔
↔
↔
↔
NaN0
NaN1
NaN2
-3 .. 40°C
PostGrid library
GeoServer
PostGrid
Image I/O
PostGrid
GeoServer
Evaluation at a direct position
Data
Operation
Interpolations
Spatial
(bicubic)
Temporal
(linear)
Final
value
Geographic Image I/O
GeoServer
PostGrid
Coverage I/O
Geographic Image I/O
Grid Coverage
Geographic Image Metadata
NETCDF
Image I/O
GML in JPEG2000
Rendered Image
ImageReader specializations
ImageReader
GeographicImageReader
FileImageReader
NetcdfImageReader
• Convenience class only; ignore if you want
• Creates IndexColorModel from (min,max) and data type
• Support for implementations that can't read a stream
• 3th dimension (often z) as bands, but doesn't have to
Geographic Image Metadata
 Subclass of IIOMetadataFormat
 Almost the only committed API
Demo
Questions?