Dead reckoning
The corresponding term in biology, to describe the processes by which animals update their estimates of position or heading, is path integration.
However, inertial navigation systems, which provide very accurate directional information, use dead reckoning and are very widely applied.
[1] By analogy with their navigational use, the words dead reckoning are also used to mean the process of estimating the value of any variable quantity by using an earlier value and adding whatever changes have occurred in the meantime.
[citation needed] While dead reckoning can give the best available information on the present position with little math or analysis, it is subject to significant errors of approximation.
These errors tend to compound themselves over greater distances, making dead reckoning a difficult method of navigation for longer journeys.
The accuracy of dead reckoning can be increased significantly by using other, more reliable methods to get a new fix part way through the journey.
Several localization algorithms based on Sequential Monte Carlo (SMC) method have been proposed in literature.
[5] In studies of animal navigation, dead reckoning is more commonly (though not exclusively) known as path integration.
Animals such as ants, rodents, and geese have been shown to track their locations continuously relative to a starting point and to return to it, an important skill for foragers with a fixed home.
[6][7] In marine navigation a "dead" reckoning plot generally does not take into account the effect of currents or wind.
Aboard ship a dead reckoning plot is considered important in evaluating position information and planning the movement of the vessel.
[8] Dead reckoning begins with a known position, or fix, which is then advanced, mathematically or directly on the chart, by means of recorded heading, speed, and time.
A naval vessel uses a device called a pit sword (rodmeter), which uses two sensors on a metal rod to measure the electromagnetic variance caused by the ship moving through water.
In this case subsequent dead reckoning positions will have taken into account estimated set and drift.
Factors including one's speed made good and the nature of heading and other course changes, and the navigator's judgment determine when dead reckoning positions are calculated.
Tools such as the traverse board were developed to enable even illiterate crew members to collect the data needed for dead reckoning.
They navigated across the Atlantic Ocean by dead reckoning and landed in County Galway, Ireland at 8:40 a.m. on 15 June completing the first non-stop transatlantic flight.
The density of the air the aircraft moves through affects its performance as well as winds, weight, and power settings.
[9] A course line is drawn on the aeronautical chart along with estimated positions at fixed intervals (say every half hour).
Dead reckoning is on the curriculum for VFR (visual flight rules – or basic level) pilots worldwide.
Many flying training schools will prevent a student from using electronic aids until they have mastered dead reckoning.
Inertial navigation systems (INSes), which are nearly universal on more advanced aircraft, use dead reckoning internally.
The proper utilization of dead reckoning in this sense would be to supply a known percentage of electrical power or hydraulic pressure to the robot's drive motors over a given amount of time from a general starting point.
Accuracy is limited by the sensor precision, magnetic disturbances inside structures, and unknown variables such as carrying position and stride length.
Another challenge is differentiating walking from running, and recognizing movements like bicycling, climbing stairs, or riding an elevator.
Custom PDR systems can take many forms including special boots, belts, and watches, where the variability of carrying position has been minimized to better utilize magnetometer heading.
Instead it used a kind of directional dead reckoning: at the start of a journey, the pointer was aimed southward by hand, using local knowledge or astronomical observations e.g. of the Pole Star.
Then, as it traveled, a mechanism possibly containing differential gears used the different rotational speeds of the two wheels to turn the pointer relative to the body of the chariot by the angle of turns made (subject to available mechanical accuracy), keeping the pointer aiming in its original direction, to the south.
In computer science, dead-reckoning refers to navigating an array data structure using indexes.
This property is particularly important for performance when used in conjunction with arrays of structures because data can be directly accessed, without going through a pointer dereference.
