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

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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