Flexibility for San Mateo Powered by OGC Standards

by Adena Schutzberg Consultant to OGC

A City like Any Other

The City of San Mateo, California is like many others when it comes to GIS. It stores its data in a relational database: SQL Server. It uses high end tools for editing, mapping and analysis: GeoMedia from Intergraph. It publishes its maps on the Web using a tool for that purpose: GeoMedia Web Map. And, like other cities, and many citizens of the world, it's enamored with Google Earth.

Geomedia display using high resolution imagery with parcels overlayed.

Dennis Wuthrich, CEO of Farallon Geographics, knows exactly why the city GIS users find the Google Earth client so compelling. "It makes accessing GIS data easier. It makes it more engaging. It's data centric. And, maybe most importantly, for those of us to close to GIS to remember, it doesn't use a traditional GIS paradigm." In fact, Google Earth's 3D look and feel can sometimes be compared to a video game.

Those reasons, and perhaps others, prompted the city to contact Farallon to ask how it could use the Google Earth client software as a front end to its GIS data. Farallon was sure it could make the connection, but the question was, "What was the best way to do so?"

Considering Standards

Wuthrich considers Farallon a systems integrator with a focus on geospatial technology, so he and his team approached the problem from that perspective. "We saw Google Earth as just one client of many that might access the city's GIS data. For us, that meant any practical solution had to be built on standards," he explained. "We imagined a service that could be accessed in the Google Earth client, and in professional GIS software clients as well."

Google Earth data for the same area.

Why standards? Wuthrich offers benefits for both his clients and his developers. "Our clients demand flexible and scaleable solutions. Using a standards-based approach, they can have access to data via both Google Earth and a high end desktop client, such as GeoMedia or ArcGIS, from a single service." His developers gain flexibility, too: they can use the same code for other projects that involve software that supports the same standards.

Further, his company, he explained, would save time developing directly using standards, since they'd need not reinvent the wheel. "Standards such as the Open Geospatial Consortium's [OCG] OpenGIS® Web Map Service (WMS) and Web Feature Service (WFS) already exist. Smart people have already figured out a way to share images (raster pictures) and vectors (map features) in a way that supports interoperability across vendor platforms." And, finally, Wuthrich notes, his team can use standard IT tools they already know to work with different XML encodings. This allowed his developers to dynamically transform map feature data (WFS vectors) into Keyhole Markup Language (KML) supported in Google Earth.

More Flexibility Thanks to Standards

In tackling the project, Farallon relied on the fact that GeoMedia Web Map supports, WMS, which defines an interface to share raster maps and WFS, which defines an interface to share details of map features (vectors). The Web Feature Services draws upon an XML encoding, Geography Markup Language, GML. GeoMedia Web Map can publish Web services using these interfaces "out of the box."

Farallon's approach involved deploying OGC services and tweaking them so that Google Earth could read them. (Google Earth currently does not act as a client to a WMS or WFS service.) Farallon had two options. The team could make changes to the Google Earth client to enable it to understand WMS and WFS. That would be difficult since Google does not offer the software code or an Application Programming Interface to enhance it. Alternatively, the team could change the data coming from the services so that Google Earth could understand it. That solution was not only possible, but relatively easy.

Google Earth uses the idea of "Network Link" to share a set of data housed on a non-Google server. Clients simply add the Network Link to their Google Earth session and the data integrates on top of data from the Google Earth servers. The Network Link is essentially a pointer to some KML, Google's XML encoding for spatial data, which supports both images and features. Farallon staff created a tool that builds, on-the-fly, the needed KML from a Web Map or Web Feature Service. Each time a Google Earth client points to the Network Link to request data, the tool creates a new, up-to-date KML file from the WMS and WFS services GeoMedia Web Map publishes.

Google Earth client view GeoMedia data via Farallon-created backend.

 

Other clients that support WMS and WFS, like GeoMedia and ArcGIS, can tap directly into the same two services used to create KML for Google Earth. That means that if it wanted to do so, San Mateo could use any other client software that supports WMS and WFS alongside Google Earth. And, in turn, if San Mateo wanted to use Google Earth to view data published by another vendor's Web mapping software that supports WMS or WFS, the tools Farallon built would work equally well to create the needed Network Links and KML.

Wuthrich is most pleased with his company's work. The project evolved over a two month period, but the technical aspects of it were accomplished quickly - in less than a month. "Using standards makes the work go faster," he explained.

Schematic of San Mateo GIS Publishing Architecture

 

Benefits

Being able to access the city's GIS data via Google Earth gets the important data "more attention" noted Wuthrich. "People who might be intimidated by a GIS application can still access, use, and benefit from the City's data"

For now, the Web maps are only accessible to city staff. Farallon and the city both look forward to opening the system to the citizens. They expect to see a whole new level of use and a whole new level of engagement when anyone, government employee, citizen, visitor or potential developer can access the most up-to-date information about the city using a familiar tool like Google Earth. Powering it all, though they may not even know it, will be several OGC standards.