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Dead reckoning is the old-school method of identifying a vehicle’s location. Conducted without digital tools like GPS or external references like landmarks, dead reckoning is a self-reliant and always usable mathematical calculation.
It dates back thousands of years when sailors in ancient Egypt, Greece and Phoenicia needed a way to navigate the coasts. This early form of dead reckoning navigation estimated positioning by tracking direction (relative to the sun or stars), rough speed and the time travelled.
The modern version of dead reckoning we use today measures acceleration, rotation and time more precisely. Despite the emergence of radio navigation and GPS tracking technology, this updated method is still widely used across vehicles and telematics as a back-up system in case external signals are lost.
What is dead reckoning navigation?
Dead reckoning navigation is an analogue way of calculating where a vehicle is based on a known starting point. As opposed to modern-day GPS technology that relies on satellite positioning, dead reckoning takes a closed-system approach by determining location through a maths equation:
New position = start position + (speed x time x direction).
While dead reckoning navigation was born from maritime activity in the ancient world, it remains relevant in the 21st century. It is a fail-safe system often combined with GPS technology in modern telematics to cover situations where GPS signals are too weak, blocked or temporarily unavailable. This is common in:
- Vehicle navigation
- Maritime navigation
- Aviation
- Robotics
How does dead reckoning navigation work?
Dead reckoning navigation works by calculating distance travelled and applying it a known starting position (identified on a map or recorded by reliable technology). By consistently measuring speed, travel time and direction, a system can update its location estimates and track a vehicle even if GPS signals become unavailable.
Starting from a known position
The key piece of information needed to perform dead reckoning navigation is a fixed start point. This is the reference against which the new positioning can be calculated. While the process itself is ‘offline’, the start point is typically established with GPS or GNSS data to avoid inaccuracies from the first moment that could cause repercussions on the subsequent estimates.
Calculating speed, direction and time
The next step is tracking how the vehicle moves over time. Speed is measured by:
- Wheel sensors or speedometers in vehicles
- Logs in ships
- Air speed indicators in aircrafts
Direction is measured with a gyroscope and time with a clock.
Estimating the current position
Having measured speed and time, you can then calculate the distance travelled:
Distance = speed x time.
Projecting the distance value calculated from the fixed starting point in the direction measured will give you a rough idea of the vehicle’s current position.
Dead reckoning navigation is a continuous loop, so, taking the current position as the new starting point, you can keep repeating the process for updated location estimates.
When is dead reckoning navigation used?
Dead reckoning navigation is primarily used as a complement to GPS systems. It is a reliable fallback when satellite signals are lost, blocked or unavailable. Let’s look at the specifics per industry and technology type:
- Private-owned vehicles
- Covers the gaps when cars travel through tunnels, underground roads or simply urban routes where GPS signals are weaker.
- Fleet management and logistics operations
- Helps maintain continuous tracking between GPS updates, ensuring accurate monitoring throughout a trip. Fleet managers need to make sure drivers are sticking to optimised routes.
- Maritime and aviation navigation
- Allows for vehicle location when underwater, in remote areas, during severe weather conditions or when there is signal interference.
- Robotics and autonomous vehicles
- Onboard sensors allow moving systems to navigate independently of external positioning signals.
Dead reckoning navigation vs GPS
GPS navigation is typically more accurate than dead reckoning navigation because it uses satellite signals, determining a vehicle’s exact position in real time. Dead reckoning, by contrast, estimates movement from a known position. In modern vehicles and telematics systems, both technologies are commonly used in tandem: GPS for accuracy over long distances and dead reckoning for maintaining positioning when signal isn’t available.
How accurate is dead reckoning navigation?
Dead reckoning navigation can be accurate in the short-term if the speed and direction values used are precise. Due to its cumulative error, however, it is better suited as a back-up approach for moments where GPS fails. Since each position estimate is based on the previous one, if there is a mistake, every position calculated from then on will drift further and further in the wrong direction.
To improve the reliability of location estimates, you can use more accurate methods (GPS, celestial navigation, radar) to take a new fixed point reading part way through the journey. Knowing your true current position, you can compare and correct your actual position, then continue with dead reckoning from that point.
Which factors affect accuracy?
- Sensor quality
- Low-quality sensors taking incorrect measurements will cause position estimates to drift in the wrong direction more quickly over time.
- Road conditions and wheel slip
- Wheels slipping and bumpy roads can cause incorrect speed measurements and distort distance calculations.
- Incorrect starting position
- Dead reckoning is based on a limited set of verified inputs, so any errors in the initial measurement will heavily impact the following estimates and compromise their accuracy.
- Changes in direction
- Poorly measured changes in direction will mean the calculated path starts to diverge from the true trace.
- Time travelled without GPS correction
- Without a GPS ‘check’ part way through a route, errors accumulate and reduce overall accuracy further.
How errors accumulate over time
Relying on previous measurements to calculate the subsequent location projections means that any mistakes made are carried through the rest of the equations and magnified. Even small error matter as they will gradually increase, causing the estimated position to drift further from the real location. The trick is to recalibrate the system at various points in the route using GPS.
Why is dead reckoning navigation important in fleet management?
Fleet managers need to know where their vehicles are at all times. Using GPS alone is therefore risky as signals can be unexpectedly interrupted by tunnels, tall buildings or areas with poor coverage.
Building the dead reckoning method into fleet technology as a failsafe improves the reliability of telematics systems and increases operational visibility. Precise vehicle tracking is critical in fleet management operations as it supports planning, efficiency and safety. It also enables fleet managers to maintain accurate journey records.
Which technologies support dead reckoning navigation?
Dead reckoning navigation requires sensors and systems to measure distance, direction and motion.
Vehicle sensors and odometers
- Wheel speed sensors: measure how fast a vehicle is moving
- Odometers: estimate the total distance travelled
- Together: their data is used to calculate positions from a known starting point
Gyroscopes and inertial systems
- Gyroscopes: measure rotation and direction changes
- Accelerometers: detect acceleration and movement across multiple axes
- Together: they form an inertial navigation system (INS) which enables continuous position estimation.
Integration with GPS and telematics systems
- GPS: provides periodic position fixes to correct accumulated error
- Telematics systems: integrate data from multiple sources for real-time tracking
- Together: the hybrid approach improves navigation reliability and tracking continuity
What are the limitations of dead reckoning navigation?
Drift and cumulative error:
Mistakes can build up as the system continues estimating location (if no GPS calibration is done mid-way through), making it increasingly unreliable for long-term positioning.
For example, when a vehicle drives through a long tunnel, the system begins with the correct position: at the tunnel entrance. It then uses wheel sensors and odometer data to estimate the movement. If the speed is overestimated, the system will predict that the vehicle has travelled further than it really has. After several minutes in the tunnel, the estimated position could end up being hundreds of metres off.
Dependence on initial position accuracy:
A key disadvantage of dead reckoning navigation is that one error affects everything that follows. However accurate your sensors are, if the starting point used was wrong, you won’t be able to get a precise location estimate.