Web Services

Web Services

At the core of the data delivery and mapping capabilities of EPSCoR Data Portal are a set of services that allow for the efficient processing of geospatial data into deliverable data and maps. These services are based upon Open Standards defined by the Open Geospatial Consortium (OGC) and are broadly supported by a large number of products, including desktop GIS systems. This page provides background information about these services, with information about how EPSCoR users can use these services to directly access EPSCoR data and map products without having to download individual data files.

General Characteristics of OGC services

Three OGC service standards are currently supported by EPSCoR, the Web Map Service (WMS), Web Feature Service (WFS), and Web Coverage Service (WCS). These standards complement each other in terms of their capabilities, with WMS delivering images representing data (i.e. maps), and WFS and WCS delivering actual geospatial data.

Common to all three service types is the GetCapabilities request which returns an XML document providing high-level information about the service (metadata) and its component layers. Additional metadata about specific features (WFS) or coverages (WCS) may be requested through the WFS GetFeatureType and WCS DescribeCoverage requests, respectively. A GetCapabilities request is a simple web address (URL) that points to the service (for example http://rgisbeta.unm.edu/dataset/ogc/wms/1608/?VERSION=1.1.1&SERVICE=WMS&REQUEST=GetCapabilities. Many client applications that can access OGC services use the GetCapabilities URL to connect with the service to determine what is available from the service. Generally, a user can provide the GetCapabilities request to the application, and it will do the rest in terms of providing access to the map layers or data products available from the service. Each application will be somewhat different in the specifics of how they access OGC services, but many already do.

To find out if your application supports one or all of these services, you can check the OGC Standards Implementation web page where there is a searchable list of applications that implement different versions of these standards.

Web Map Services (WMS)

WMS provides map images for one or more layers provided by a given service. By default, each geospatial dataset in this portal is published as a single layer WMS both for use within this portal and for use by outside applications. WMS is oriented towards the provision of mapped data (an image representing the data, not the actual data themselves) in response to the GetMap request. The attributes of specific features may be requested through the WMS GetFeatureInfo request.

In contrast, the WFS and WCS standards provide request methods that return geospatial data suitable for use in GIS or other geospatial analysis environments.

Web Feature Services (WFS)

WFS specifies two request types that return geospatial feature data, the GetFeature and GetGmlObject requests. Both of these requests may return a subset of features, in Geography Markup Language (GML, an OGC Extensible Markup Language [XML] grammar for representing vector geographic data and associated attributes) or another specified and supported geospatial data format, that meet query and other criteria specified in the request.

Web Coverage Services (WCS)

WCS provides data access functionality through the GetCoverage request. A WCS will provide raster geospatial data (a coverage) in at least one of five specified formats (GeoTIFF, HDF-EOS, DTED, NITF, or GML), and may provide the data in other formats, if configured to do so.

Accessing NM EPSCoR Data Portal OGC Services

The GetCapabilities requests for available OGC services for each data product are available both from the pop-up tool bar available for all downloadable data sets, and from the quick preview pane.

The link to the GetCapabilities requests from the preview pane are available from the OGC Services link at the right side of the menu bar in the preview window (Figure 1). Similarly, the same service information is directly available from the data set tool interface (Figure 2).

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Figure 1, Menu bar from the data set preview interface, with OGC service link circled

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Figure 2, Menu bar from the data set tool interface, with OGC service link circled

Application-specific OGC Service Access Information