Transcript WCS Data Exchange at the DataFed Server/Client

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
Huntsville, AL
March 2006
Team: Rudolf Husar
Stefan Falke
Kari 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
WCS getCoverage for Map View
WCS getCoverage for Time View
Returned NetCDF file grid file
Client uses Unidata netCDF C library
getCoverage
Height View
Each View is a slice through the
4D data cube
Multidimensional AQ Monitoring Network Data Storage and Delivery through OGC Protocols
WCS Data Access
WCS
Stations
SOS
Observations
Station Info.
Relational
Data Model
Observations
Param/Sensor/Method
Star
Schema
Par-Meth
SOS
WFS
Data View Services
SensorML
WMS
WMS
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 OR
gml: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
Multidimensional
Data Cube
Most Views are slices through a cube of
data organized by lat, lon, altitude, and
time (X,Y,Z,T)
Data Access through Adapters
Sources
Data Wrapper
Virtual Data Cube
Query Adapter
Output
Diverse formats
Many data models
Data into geo-cubes
Queries to views
Global geo-cube data model
Makes queries data-neutral
Maps query to protocol
User selects protocols
Protocol dependent
User specified
Station-Point
SQL Server, Files…
DataFed
GeoTable
SOAP,HTTP Get
CSV,XLS,GML
Sequence
Image, file
OGC WCS
GeoGrid
HTTP Get, Post
GML,NetCDF..
OGC WMS
GeoImage
HTTP Get
GeoTIFF, PNG..
through
nDim Grid
OpenDAP NetCDF,
…
Other
Traject., Event, Pic
OGC WFS
Other
HTTP Get, Post
MS Dataset..
DataFed
An application framework for accessing, processing and browsing
distributed datasets using loosely coupled web service components
www.datafed.net