By George Percivall, Open Geospatial Consortium (OGC)
The introduction of geospatial technologies such as Google Earth™, Microsoft® Virtual Earth™, ESRI’s ArcGIS™ Explorer and other Earth visualization systems has greatly increased the number of computer users who think about geography and Earth Observations (EO). People can now easily visualize what their next trip or hike will look like; they can readily combine EO data (such as aerial photos and satellite images of Earth) with other kinds of geographic data (such as road maps, address databases, or building models draped on an elevation model); and they can easily save the views they have constructed and send them to other users.
However, geospatial technologies are more complex than most people realize. Consider the visual differences between roadmaps, satellite and aerial imagery, subway maps, and spreadsheet lists that contain street addresses. Consider, too, the different projection systems (Mercator, Sinusoidal, and Lambert Conformal Conic, for example) used to represent the Earth’s spherical surface on a flat surface. And consider that the location of a point described in longitude, latitude and elevation is uncertain if one doesn’t know which “geoid,” or ellipsoidal model of our not-perfectly-spherical Earth these coordinates refer to. Taken together, a projection, a datum defining the starting point of the coordinates, and an ellipsoid comprise a coordinate reference system, and an application must define all three to return correct locations. The “maps that don’t match” problem becomes more complex when you consider the diverse formats that derive from the diverse market goals and technical approaches of different geospatial software developers. And even more complexity is added when you consider that different user communities may have different naming schemas and visual presentation rules for the same geospatial information.
Just as standardization has been a critical factor in the growth of the Internet and the Web, standardization will play an important role in the growth of the “Geospatial Web” that prominently includes these Earth visualization systems.
OGC: Beyond Geo-Babel
The OGC is an organization uniquely focused on developing standard interfaces, encodings and best practices, through international consensus, that enable software developers to manage the complexity of geospatial technologies and make different geospatial information systems that communicate or “interoperate.”
Google and Microsoft have recently joined the 353 other Strategic Members, Principle Members, and additional voting and nonvoting members of the OGC, which has substantially enhanced the Consortium’s ability to realize its vision of geospatial interoperability for wide application. For example, last year Google and Galdos Systems introduced Google’s KML, an open encoding schema, into the Open Geospatial Consortium, Inc. (OGC(R)) standards process, and in April 2008, KML version 2.2 was officially adopted by the OGC membership as an OGC standard (see http://www.opengeospatial.org/standards/kml.) KML (originally Keyhole Markup Language) is now the OGC standard for annotation and visualization on existing or future web-based online maps (2d) and Earth browsers (3d), from any provider. Through the OGC standards process, KML has become more aligned with international best practices and standards, thereby enabling greater uptake and interoperability of Earth browser implementations. KML 2.2’s consistency with the OGC’s other standards (http://www.opengeospatial.org/standards) means that developers will face fewer obstacles bringing content from other kinds of geospatial systems into Earth visualization systems. For example, work products created using a Geographic Information System (GIS), tracking system, Earth imaging system, or “sensor web” (Web-based sensor network) will be easily displayed with other data employing widely used browser-based systems. Similarly, data encoded in GML (OGC’s Geography Markup Language Encoding Standard) from applications implementing the OGC Web Feature Service (WFS) standard can readily be styled to KML for visual presentation.
Geospatial Technology for Everyone
Earth browsers represent not a new technology, but a new business model characterized by free base data, a free geospatial Web service, and, now an open encoding schema, KML, for geographic annotation and visualization. KML enables anyone to define mapped data for presentation in Google Earth or other Earth browsers. For example, a KML file could contain locations of hiking trails (stored as GPS coordinates or street addresses) overlaid on a highway map or on remotely sensed imagery of a wilderness area (Figure 1). These applications are sometimes called “mash-ups”. Both Virtual Earth and ArcGIS Explorer, like Google Earth and Google Maps, can use KML input, so similar mash-ups are possible with those Earth visualization systems.
Microsoft has already implemented the OGC Simple Features SQL standard (http://www.opengeospatial.org/standards/sfs) and GeoRSS GML (http://www.opengeospatial.org/pressroom/pressreleases/580). Oracle has been an important contributor since 1995. The OGC’s Strategic Members (highest level) and Principal Members are listed below:
BAE Systems – C3I Systems
ERDAS, Inc. (formerly Leica Geosystems Geospatial Imaging)
Northrop Grumman TASC
US Geological Survey (USGS)
US National Aeronautics and Space Administration (NASA)
US National Geospatial-Intelligence Agency (NGA)
Bentley Systems, Inc.
Department of Science & Technology, India
EADS ASTRIUM, France
GeoConnections – Natural Resources Canada
PB MapInfo Corporation
PCI Geomatics Inc.
Rolta India, Ltd.
US Department of Homeland Security (DHS)
WhereGroup GmbH & Co. KG
There also 57 other voting members of the Technical Committee and 275 non-voting members of the consortium.
Active involvement by organizations such as Google and Microsoft strengthens the OGC’s role in shaping the policies and best practices needed to grow and support development of effective, worldwide spatial data infrastructures and sensor webs. For consumers and for stakeholders who are dealing with global issues such as climate change and disaster preparedness, it is fortunate that the work of the Consortium is supported by the deep infrastructure and information resources that these companies represent.