DataFed OGC WMS Server
The most widely used Open Geospatial Consortium (OGC) specification is the Web Mapping Server (WMS) protocol for transferring maps and georeferenced data over the Internet. Data from WMS servers deliver georeferenced map images to standard Web browsers. Through a standard HTTP Get URL call, the user specifies the data desired layers to be overlaid, their image size and format, geo-rectangle and another parameters. If the URL call is made by a custom viewer, the returned OGC image can be overlaid with other georeferenced maps and data.
DataFed OGC WMS Server
Spatial data views from DataFed can be requested through the OGC standard WMS interface. To support such a request, DataFed can respond to two HTTP requests: (1) The GetMap request for user-selected data layers and spatial subsets and (2) The GetCapabilities request for describing the Web Map Server capabilities as an XML file. DataFed serves The DataFed WMS GetCapabilities documents describe available datasets and their properties that can be retrieved. The GetCapabilities documents are organized by data provider (a single GetCapabilities document with all datasets is large and causes many WMC clients to time-out). The data providers listed below correspond to the provider classifications in the DataFed Catalog.
EPA: http://webapps.datafed.net/ogc_EPA.wsfl?SERVICE=wms&REQUEST=GetCapabilities&VERSION=1.1.1
NASA: http://webapps.datafed.net/ogc_NASA.wsfl?SERVICE=wms&REQUEST=GetCapabilities&VERSION=1.1.1
NCDC: http://webapps.datafed.net/ogc_NCDC.wsfl?SERVICE=wms&REQUEST=GetCapabilities&VERSION=1.1.1
TOMS: http://webapps.datafed.net/ogc_TOMS.wsfl?SERVICE=wms&REQUEST=GetCapabilities&VERSION=1.1.1
UniData: http://webapps.datafed.net/ogc_UniData.wsfl?SERVICE=wms&REQUEST=GetCapabilities&VERSION=1.1.1
USDAFS: http://webapps.datafed.net/ogc_USDAFS.wsfl?SERVICE=wms&REQUEST=GetCapabilities&VERSION=1.1.1
CAPITA: http://webapps.datafed.net/ogc_CAPITA.wsfl?SERVICE=wms&REQUEST=GetCapabilities&VERSION=1.1.1
Each GetCapabilities call will return a document listing the map layers from a particular data source that can be retrieved through DataFed.
The required elements of an OGC WMS GetMap request include:
The WMS service facilitates the exchange of spatial (map image) data. The OGC WMS versions 1.1.1 and allow data requests to multidimensional data. Therefore, through WMS, spatial 'slices' can be requested and served by specifying 'other' data dimensions, such as TIME, ELEVATION, WAVELENGTH, etc.
The datasets in DataFed are inherently multi-dimensional with SPACE and TIME being the most commonly used data dimensions. As a result, the OGC WMS interface to DataFed makes use of the optional TIME element in the GetMap request.
The TIME
element
The TIME parameter extends the standard OGC WMS GetMap request by allowing the specification of a specific time or time range for which to retrieve the WMS map. DataFed has implemented the TIME parameter to support a single date/time. Future plans are to support a time range (start time, end time).
Two example requests from DataFed using the TIME element:
TOMS_AI satellite image data for specific day
Surface Meteorology Observations extinction coefficient point data for specific
day and hour:
Web Clients that support the TIME parameter in the
OGC WMS GetMap Request
NASA WMS viewer: http://map05.gsfc.nasa.gov/cgi-bin/aerosol.cgi
OWSView: http://cgdi-dev.geoconnections.org/prototypes/owsview/
Space-time Toolkit: http://vast.nsstc.uah.edu/SpaceTimeToolkit/
DataFed Viewer: http://webapps.datafed.net/datafed.aspx (described here)
For developers: UMN MapServer (http://mapserver.gis.umn.edu/doc42/wms-client-howto.html)
Building a GoogleMaps application that uses WMS layers: