26 Copyright © 2011 Open Geospatial Consortium,
Inc. All Rights Reserved.
Feature types available from the FPS are: Airspaces
Airports Heliports Navaids
Runways Routes
Taxiways
7.3.2.5 Component Configuration
Envitia’s ChartLink application is the nucleus of the system. It is running on the server and is accessed via the Envitia Web Services WMS component in order to service
requests.
The data from the source WFSs provided by Luciad, COMSOFT and Snowflake has been pre-processed and cached.
7.3.2.6 Challenges Faced
One of the main challenges faced with Envitia’s approach was matching up third party SLDs with the internal storage format of the cached data in ChartLink. ChartLink
provides the images required in servicing FPSWMS requests and is therefore responsible for rendering using SLDs. Its internal storage method is not synonymous with the GML
and XPath aspects related to the usage of the SLD and WFS standards.
Due to the complexity of some of the portrayal issues, and to the lack of support for some of the optional WFS capabilities, such as XPath resolution and join predicates, most of
them were not possible to display in the demonstration portal.
Other issues identified have been articulated in the Aviation Portrayal ER see OGC 11-089.
7.3.2.7 OWS-8 Accomplishments
A number of the more complex portrayal issues were explored with the use of this component. This supported the significant contribution to the Aviation Portrayal
Engineering Report from Envitia.
One of the benefits to Envitia’s approach of caching the WFS data was that it permits Envitia control over the data itself, which enabled modification of key attribute values.
This is instrumental in being able to ensure that the different symbols and symbology challenges can be exercised. As a simple example, this has meant that Envitia can ensure
that there are runways with UNSERVICABLE status within the areas of interest.
Copyright © 2011 Open Geospatial Consortium,
Inc. All Rights Reserved.
27
7.3.3 Luciad
Luciad provides an OGC Feature Portrayal Service FPS to portray GML data. An FPS service takes away the burden of parsing and visualizing raw GML data served by a
WFS. It remotely loads and renders data, and returns the result as an image that can be shown by any modern web browser.
The FPS was provided as an in-kind contribution because it entirely relied on standards and did not need any code specific to the project. In fact, the same setup is also used in
other OGC projects.
Using an FPS in an application consists of the following high-level steps: 1.
Determine the WFS server that is to be contacted by the FPS 2.
Construct a query for the WFS server to select the required data 3.
Create a Symbology Encoding SE feature type style to render the data from the WFS server
4. Wrap the WFS query together with the SE style in a request and send it to the FPS
The major drawback of this scenario is that it does not allow for caching of the data on the server, mainly because it cannot be predicted what data will be requested by the user.
To circumvent this, the FPS can also offer layers, much like a traditional WMS, and allow dynamic styling of those layers. This is also supported by our FPS component.
One other possible improvement would be an FPS that shares a data store with a WFS. This would allow advanced querying and styling capabilities, but would not support
interaction with multiple WFS services.
Another useful enhancement would be support for vector-based output formats, such as KML and GeoJSON. This could also benefit map display performance, as the client
application would no longer need to request new images every time a user zooms or pans.
Technical specifications
The FPS was built using the OGC-compliant web service components provided by Luciad. The most important features include:
Support for OGC WMSFPS versions 1.1.1 and 1.3.0, including GET and POST requests
Support for OGC WFS versions 1.0, 1.1 and 2.0, including SOAP requests Support for OGC SLDSE versions 1.0 and 1.1
Support for any kind of GML application schema, such as WXXM and AIXM. Full support to work with AIXM 5.0 5.1, including the temporality model
