WCS Data Exchange at the DataFed Server/Client
Center for Air Pollution Impact and Trend Analysis (CAPITA)
Washington University, St. Louis, MO
OGC TC Meeting
Team: R. B. Husar S. R. Falke K. Hoijarvi
GALEON IE – Examples DataFed as WCS Client
U Florence/CNR-IMMA WCS Server THREDDS 4D (Time, X, Y, Z, H) data
getCoverage for Map View
getCoverage for Time View
Surface Temp. dataset; Time, Lat, Lon
Uniform spatial grid Each View is a slice through the
4D data cube
WCS getCoverage for Map View
WCS getCoverage for Time View
Returned NetCDF file grid file
Client uses Unidata netCDF C library
Multidimensional AQ Monitoring Network Data Storage and Delivery through OGC Protocols
WCS Data Access
WMS Data View Services
Stations Observations Par-Meth
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:
Suggested Changes to WCS 1.1 Table 17 (SpatialDomain)
Name Definition Data type Multiplicity and use
BoundingBox Unordered list of bounding boxes whose ows:BoundingBox One or more (mandatory)
union covers spatial domain of this
coverage offering a
Grid Unordered (TBR) list of grids that describe gml:Grid OR Zero or more (optional)
internal grid structure of this coverage gml:RectifiedGrid Include one for each
offering b different grid used
Polygon Unordered list of polygons whose union gml:Polygon Zero or more (optional)
covers spatial domain of this coverage Include one for each polygon
offering c needed
Point Unordered list of points whose union gml:Point OR Zero or more (optional)
covers the spatial domain of this gml:Position OR Include one for each point
coverage offeringd om:
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
Data Model for Air Quality Data
Data Cube Most Views are slices through a cube of
data organized by lat, lon, altitude, and
Data Access through Adapters
Sources Data Wrapper Virtual Data Cube Query Adapter Output
Diverse formats Data into geo-cubes Global geo-cube data model Maps query to protocol Protocol dependent
Many data models Queries to views Makes queries data-neutral User selects protocols User specified
SQL Server, Files… DataFed GeoTable
SOAP,HTTP Get CSV,XLS,GML
Image, file OGC WCS GeoGrid
HTTP Get, Post GML,NetCDF..
OpenDAP NetCDF, OGC WMS GeoImage
… HTTP Get GeoTIFF, PNG..
Other OGC WFS Other
Traject., Event, Pic HTTP Get, Post MS Dataset..
An application framework for accessing, processing and browsing
distributed datasets using loosely coupled web service components
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.
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)."