After being conceived in the 1970s, GPS took about two decades to evolve into an accessible and powerful system for civilian use. Most modern GPS receivers rely on a large internal database, which allows GPS units to automatically translate their computed latitude/longitude coordinates into real-world roads and addresses. DVD navigation systems are a subset of satellite navigation systems usually installed in vehicles.
Beginning in the 1940s, early electronic navigation systems such as LORAN and Transit could be used only in certain locations and sometimes required several hours to provide a position fix within a few hundred meters. The utility of such systems was limited, and the military determined its own need for a more accurate and timely way to confirm one's position.
In the early 1970s, Defense Department navigation specialists conceived of using a constellation, or network, of several dozen satellites to provide rapid and highly accurate positioning information across the entire planet.
How GPS Works
GPS satellites are monitored from sophisticated ground stations and informed about their own orbital location and path above the planet. Each satellite then broadcasts its position, along with a very precise time reading, back down to the planet.
By comparing the respective satellites' orbital positions, along with the precise timing data of each signal, a GPS receiver computes the "solution": the only location on Earth that is compatible with the signals it's receiving. This is the GPS unit's location.
While pure latitude-longitude data is useful for some applications, most citizens need a navigation system to present information in a user-friendly and readily understandable format. Rapid miniaturisation and processing-power increases in computing in the 1990s enabled GPS systems that included a large on-board database.
Instead of displaying pure numerical coordinates, GPS receivers could compute the latitude and longitude in the background, and automatically translate them into street addresses and an onscreen image, accomplished by rapid and automatic lookup in a large on-board database of locations.
Storing the Database
Early-generation graphical GPS receivers held their location databases in on-board solid-state memory storage chips. These databases could be gradually made larger and more accurate as memory chip capacity increased.
Evolving technology also enabled users to begin adding memory and additional databases by inserting SD storage cards. As DVD technology emerged in the early 2000s, GPS manufacturers recognised that it would allow the storage of very large databases on fairly inexpensive DVDs.
Moving to DVDs
The impressive storage characteristics of DVDs (generally a minimum of 4.7 GB), and the opportunities unlocked by the automotive environment, made them an attractive choice for holding the lookup databases of certain built-in GPS navigation systems.
The size of DVDs, and the weight and power requirements of their mechanised players, make them a poor match for handheld GPS systems. In automobiles, however, electricity is constantly generated by the alternator, and bumps and shocks dampened by the suspension. Here a built-in GPS system could take advantage of DVDs' large and inexpensive data storage, and provide drivers with new levels of navigation detail.
Advantages and Disadvantages
The largest advantage of GPS systems that use DVD databases, compared with standard on-board memory, is their ability to present enormous detail about routes and points of interest. Many automakers' systems include features such as searchable nationwide telephone directories, restaurant and hotel ratings.
However, database upgrades can often be more difficult and expensive with built-in DVD-based GPS systems. The DVDs are usually proprietary to each car make and sometimes model, and are often only available from the dealer or manufacturer and/or at high cost. Because they rely on proprietary DVDs, such systems can't be upgraded over the Internet.