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WCS Data Exchange at the DataFed Server/Client
Center for Air Pollution Impact and Trend Analysis (CAPITA)
Washington University, St. Louis, MO
OGC TC MeetingHuntsville, ALMarch 2006
Team: Rudolf Husar Stefan Falke Kari Hoijarvi
GALEON IE – Examples DataFed as WCS Client
Surface Temp. dataset; Time, Lat, LonUniform spatial grid
WCS getCoverage for Map ViewWCS getCoverage for Time View
Returned NetCDF file grid fileClient uses Unidata netCDF C library
U Florence/CNR-IMMA WCS Server THREDDS 4D (Time, X, Y, Z, H) data
Each View is a slice through the 4D data cube
getCoverage for Time View
getCoverage for Map View
getCoverage Height View
Multidimensional AQ Monitoring Network Data Storage and Delivery through OGC Protocols
Relational Data Model
Star Schema
WMS
WCS SOS
Sen
sorMLW
FS
Observations
Sta
tion
In
fo.
Para
m/S
en
sor/M
eth
od
Data View ServicesW
MS
Stations Par-Meth
Observations
SO
S
WCS Data Access
DataFed WCS Server for Point Observation Data
The current version of WCS (1.0) only supports grid and image data types.
Coverages can include other representations of space-time varying phenomena, such as observations from an air quality monitoring network.
An example WCS query for a point dataset in DataFed is:
http://webapps.datafed.net/dvoy_services/ogc.wsfl?SERVICE=wcs&REQUEST=GetCoverage&VERSION=1.0.0&CRS=EPSG:4326&COVERAGE=AIRNOW.pmfine&FORMAT=CSV&BBOX=-125,22,-61,51,0,0&TIME=2005-06-27T15:00:00Z&WIDTH=999&HEIGHT=999&DEPTH=999
&BBOX=-100,22,-100,22,0,0&TIME=2005-06-20T00:00:00Z/2005-06-30T23:00:00Z
Suggested Changes to WCS 1.1 Table 17 (SpatialDomain)
Name Definition Data type Multiplicity and use
BoundingBox Unordered list of bounding boxes whose union covers spatial domain of this coverage offering a
ows:BoundingBox One or more (mandatory)
Grid Unordered (TBR) list of grids that describe internal grid structure of this coverage offering b
gml:Grid ORgml:RectifiedGrid
Zero or more (optional)Include one for each
different grid used (TBR)
Polygon Unordered list of polygons whose union covers spatial domain of this coverage offering c
gml:Polygon Zero or more (optional)Include one for each
polygon needed
Point Unordered list of points whose union covers the spatial domain of this coverage offeringd
gml:Point OR gml:Position OR om: featureOfInterest
Zero or more (optional)Include one for each point
a One bounding box could simply duplicate the information in the ows:WGS84BoundingBox; but the intent is to describe the spatial domain in more detail (e.g., in several different CRSs, or several rectangular areas instead of one overall bounding box).
b This element can help clients assess the fitness of the gridded data for their use (e.g. its native resolution, inferred from the offsetVector of a gml:RectifiedGrid), and to formulate grid coverage requests expressed in the internal grid coordinate reference system.
c Polygons are particularly useful for areas that are poorly approximated by a ows:BoundingBox (such as satellite image swaths, island groups, other non-convex areas).
d Points are useful for representing samples or observations from monitoring networks, such as soil samples or temperature measurements from weather stations, where the phenomena being measured is continuous over the spatial range but is measured only at a limited number of locations
Extra Discussion Slides
---The current WCS SpatialDomain requires BBOX. (Grid, Polygon, (or, in the future, Point) are optional). One could argue that if Polygon (or, in the future, Point) are specified, a BBOX is not required. So, SpatialDomain is mandatory and can be specified using one (or more) of BBOX, Grid, Polygon or Point.
---The current version of the WCS requires either a WIDTH,HEIGHT,DEPTH or RESX,RESY,RESZ to specify the size or resolution of the returned grid. When other non-grid data types are supported (polygon, point) these should be made optional since they are not relevant with non-grid data types.
---The current WCS specifies output formats. An table output format(s) will need to be added. This might include simple CSV tables or XML based tables. For example, DataFed supports CSV, .NET DataSet, and a netCDF table, which is a special table format, that will be adapted through future testing and to more standard formatting conventions.
Coverage Definitions
OGC Coverage Abstract Specification: "A coverage can be designed to represent a single feature, or a set of features. For example, a coverage may have a spatial domain containing a single parcel, or an entire platt. In the latter case, the coverage may be treated as modeling a single feature (the platt), or as a collection of features (the collection of parcels)."
WCS 1.1 (draft): "Unlike WFS [OGC 02-058], which returns discrete geospatial features, the Web Coverage Service returns coverages representing space-varying phenomena that relate a spatio-temporal domain to a (possibly multidimensional) range of properties."
Ron Lake, Galdos: "Loosely speaking a coverage is a sort of generalization of a geographic image - meaning it specifies the geometry of the coverage in some geographic space (e.g. some part of the earth's surface) and defines a function on that space. In image terms you can think in terms of the geometry as the image "grid" and the function as the radiometry or pixel values. The geometry can be a gridded structure (like most raster images) or can be a tesselated field, collections of polygons, a set of curves or curve segments or just a random collection of points. The function provides values at these points - such as soil samples (random point collection), road surface type (curve segments), crop type (polygons) and brightness (gridded image)."
Data Model for Air Quality Data
Most Views are slices through a cube of data organized by lat, lon, altitude, and time (X,Y,Z,T)
Multidimensional Data Cube
through
Data Access through Adapters
DataFed SOAP,HTTP Get
OGC WCS HTTP Get, Post
OGC WMS HTTP Get
Station-Point SQL Server,
Files…
Sequence Image, file
nDim Grid OpenDAP NetCDF,
…
Other Traject., Event, Pic
Sources Diverse formats
Many data models
Data Wrapper Data into geo-cubes
Queries to views
Virtual Data Cube Global geo-cube data model Makes queries data-neutral
Output Protocol dependent
User specified
GeoTable CSV,XLS,GML
GeoGrid GML,NetCDF..
GeoImage GeoTIFF,
PNG..
Other MS Dataset..
Query Adapter Maps query to protocol
User selects protocols
OGC WFS HTTP Get, Post
DataFed
www.datafed.net
An application framework for accessing, processing and browsing distributed datasets using loosely coupled web service components