Copyright © 2006 Open Geospatial Consortium – All rights reserved
53 offering, the client can now construct a WCS GetCoverage request and retrieve a result in
a form of one of the formats supported by the WCS.
12.2 Issues and Tradeoffs with Web Feature Service Communication
Although used and implemented within the OWS-3 testbed, Web Coverage Services were not a focal point of the demonstrations for the integrated clients. Part of the reason for
this might be due to the spotlight given to WCS during the OWS-2. It is believed that many of the issues and concerns dealing with a coverage service were discussed and dealt
with during that interoperability testbed.
12.3 Implementation Comments
12.3.1 Intergraph Corporation
The user supplies the WCS endpoint to the connection service and the service makes a GetCapabilities request as the initial communication to the service. The list of available
coverage offering are then presented to the user along with a number of metadata elements describing each coverage offering. The user selects the appropriate coverage
and enters information about how to retrieve the image including bounding box, sampling, and return format information. Then a GetCoverage request is issued and the
image is returned to the client.
Once the image is returned to the client, it is written to local memory and stored in a warehouse connected to the commercial GeoMedia platform. At this point the recently
acquired image is added to the MapView legend using standard commercial rendering capabilities based on the return format of the image.
12.4 Recommendations
Since the WCS was not a focal point in this testbed, it was not addressed to the detail that would reveal items to be discussed as future recommendations. However, due to the
efforts undertaken as part of the OWS-2 interoperability experiments, many recommendations have are already being addressed.
54
Copyright © 2006 Open Geospatial Consortium – All rights reserved
13 Catalog Service for the Web CS-W
It is believed that the ability to discover geospatial resources is an important role for any integrated client. The OGC Catalog Service for the Web is an abstract specification. That
abstract specification serves as the basis for specifications that can be implemented called profiles. OGC has currently defined three profiles of the catalog specification:
CSW Record profile ebRIM profile, and
ISO profile. At its core, an ebRIM catalog stores two kinds of objects: extrinsic objects and service
objects. There are two classes of extrinsic objects: those that exist by virtue of a service, and those that exist independently of a service. Examples of the latter include data sets,
schemas and symbology encoding documents. Examples of extrinsic objects that exist by virtue of a service include layers WMS, feature types WFS and observation offerings
SOS.
A service and its related objects typically make their way into a catalog via a harvesting operation. The harvesting operation generally ingests a capabilities response from a
service and populates the catalog with a service object and a set of extrinsic objects that represent the collection of objects on which that service operates.
13.1 Direct Access to a Catalog Service for the Web CS-W
Direct communication with a Catalog Service for the Web allows a user to query and retrieve information about various web services based on criteria such as bounding box
and keywords. This allows the user to review the metadata about a given service prior to executing a request for information.
In the following example, an integrated client is used to connect to and retrieve metadata published through a Catalog Service for the Web. It is recognized that this example is
only a small scope of the catalog retrieval functions and is meant only as an example of an implementation within the framework of the OWS-3 testbed.
Copyright © 2006 Open Geospatial Consortium – All rights reserved
55
Intergrated Client CS-W
GetRecords Service_Query Service Endpoints
GetRecords EO_Query Extrinsic Objects
Figure 18 Catalog Retrieval
In this example an integrated client is provided with the URLs of the Catalog Service endpoints. Based on user input, a query is constructed with which a GetRecords request
is made to find Extrinsic Objects based on the object type FeatureType, WMS_Layer, ObservationOffering. The response will include the objects identified along with
metadata about the object including an id for each object. Another GetRecords request can then be constructed to build a Service request to identify the service endpoints for
each object. With this information the user has the information needed to bind to the appropriate data.
13.2 Issues and Tradeoffs with Catalog Service for the Web Communication
