GPS with dead reckoning is a way for a global positioning system to keep track of an individual's automobile after a satellite signal has been lost. The feature is available on many high-end GPS models for automobiles. GPS with dead reckoning works by still being able to monitor a vehicle's speed and course of direction, but is somewhat less accurate than true satellite guidance. Dead reckoning technology becomes less accurate the longer the GPS system is out of contact with the satellites.
The main advantage of GPS with dead reckoning is that it continues to monitor the course of a vehicle that has lost a satellite signal. This may happen, for example, in locations where there are mountains, tunnels or large buildings. While current GPS technology is relatively reliable, there still may be cases when an insufficient number of satellites are available to triangulate a fix, which is where dead reckoning functionality is so useful.
GPS with dead reckoning could utilize a number of different techniques to help provide navigational services when satellites are not available. Some systems simply measure the average speed for a stretch of road based on the most recent data from the automobile and continues projections at that rate of pace. Others may use a digital compass and a connection to the car's internal sensors to help determine what the speed and direction of the automobile is to provide as detailed information as possible.
Motorists using GPS with dead reckoning should be aware that these backup methods will never be as accurate as satellite data. Most GPS models will, by default, warn the motorist when the satellite information is no longer available and a backup method is being used. Motorists should always keep this option on so that there is no question about what information the system is relying upon to give directions.
Given the fact that GPS with dead reckoning will always make some assumptions in order to provide as much information as possible, the longer the satellites are not available, the greater the chances are for inaccurate information. Therefore, motorists who may be making turns soon after satellites are lost will need to be especially aware. Directions may still be relatively accurate, but everything should be verified.
Some GPS units using dead reckoning technology require more hardware than a standard system. This hardware may be connected to the car's speedometer so that the unit can accurately measure speed. Those not comfortable doing this will need to take the system to a professional installer before those capabilities are available.