A number of different tracking technologies are under development, each with its own specs.
Nielsen Outdoor uses the GPS-based NPOD, presented on last Friday's Investor Day, for tracking vehicles. The device is based on patents that allow it to use just one satellite feed, instead of the usual three for triangulation. The information is combined with a map of all billboard locations, with their orientation. Nielsen intends this new product to be the currency for the outdoor advertising market. Roll-out starts in 2006 in South Africa, Australia and Italy.
Navicom GPS runs a trial at the Southern California Fire Department, testing a device that is supposed to allow tracking in 98% of North America. The instrument is also GPS-based (like e.g. Nextel's GPS Platform, for fleet management). Fire engine vehicles have access to restricted areas, which makes this service especially relevant these days.
Skyhook Wireless on the other hand uses its own proprietary database of 1.5 million private and public Wi-Fi hotspots in the US, including their exact locations, for its Wi-Fi Positioning System (WPS). It offers better resolution than GPS (up to 20 meters). WPS could be used for an array of location-based services, such as tracking & recovery, m-commerce, fleet management and E911-compliance. The FCC mandates E911-compliance by September 2005 for VoIP-providers, meaning that callers must be traceable (Skype will not comply, saying that it regards itself a secondary line service).
Aside, the EU is preparing the 2008 launch of Galileo, both competing and complementing US-originated GPS.