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Navigator zacrta svoj položaj od 9:00, naznačen trouglom, i, koristeći svoj kurs i brzinu, proceni vlastiti položaj u 9:30 i 10:00.

U navigaciji, izračunavanje koordinata je proces izračunavanja nečiji trenutnog položaja pomoću prethodno određenog položaja, ili fiksiranja, korišćenjem procena brzine i kursa tokom proteklog vremena. Odgovarajući termin u biologiji, koji se koristi za opisivanje procesa pomoću kojih životinje ažuriraju svoje procene položaja ili smera, jeste integracija putanje.

Zanošenje je ugao između pravca aviona i željene staze. A je poslednji poznati položaj (fiks, obično prikazan krugom). B je vazdušni položaj (obično se prikazuje znakom plus). C je položaj DR (obično se prikazuje trouglom).

Izračunavanje koordinata je podložno akumulaciji grešaka. Napreci u navigacionim pomagalima koji daju tačne informacije o položaju, posebno satelitskoj navigaciji koja koristi globalni pozicioni sistem, pojednostavili su izračunavanja koordinata, tako da su tradicionalni proračuni zastareli za većinu svrha. Međutim, inercijalni navigacioni sistemi, koji pružaju vrlo tačne informacije o pravcu, koriste izračunavanje koordinata i veoma su široko zastupljeni.

Greške

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. For precise positional information, both speed and direction must be accurately known at all times during travel. Most notably, dead reckoning does not account for directional drift during travel through a fluid medium. These errors tend to compound themselves over greater distances, making dead reckoning a difficult method of navigation for longer journeys.

For example, if displacement is measured by the number of rotations of a wheel, any discrepancy between the actual and assumed traveled distance per rotation, due perhaps to slippage or surface irregularities, will be a source of error. As each estimate of position is relative to the previous one, errors are cumulative, or compounding, over time.

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. For example, if one was navigating on land in poor visibility, then dead reckoning could be used to get close enough to the known position of a landmark to be able to see it, before walking to the landmark itself — giving a precisely known start point — and then setting off again.

Lokalizacija mobilih sensorskih čvorova

Localizing a static sensor node is not a difficult task because attaching a GPS device suffices the need of localization. But a mobile sensor node, which continuously changes its geographical location with time is difficult to localize. Mostly mobile sensor nodes within some particular domain for data collection can be used, i.e, sensor node attached to an animal within a grazing field or attached to a soldier on a battlefield. Within these scenarios a GPS device for each sensor node cannot be afforded. Some of the reasons for this include cost, size and battery drainage of constrained sensor nodes. To overcome this problem a limited number of reference nodes (with GPS) within a field is employed. These nodes continuously broadcast their locations and other nodes in proximity receive these locations and calculate their position using some mathematical technique like trilateration. For localization, at least three known reference locations are necessary to localize. Several localization algorithms based on Sequential Monte Carlo (SMC) method have been proposed in literatures.[1][2] Sometimes a node at some places receives only two known locations and hence it becomes impossible to localize. To overcome this problem, dead reckoning technique is used. With this technique a sensor node uses its previous calculated location for localization at later time intervals.[3] For example, at time instant 1 if node A calculates its position as loca_1 with the help of three known reference locations; then at time instant 2 it uses loca_1 along with two other reference locations received from other two reference nodes. This not only localizes a node in less time but also localizes in positions where it is difficult to get three reference locations.[4]

Životinjska navigacija

Glavni članak: Životinjska navigacija

In studies of animal navigation, dead reckoning is more commonly (though not exclusively) known as path integration. Animals use it to estimate their current location based on their movements from their last known location. 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.[5][6]

Pomorska navigacija

Alati za izračunavanje navigacionih koordinata u obalnoj plovidbi

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.[7]

Autonomna navigacija u robotici

Dead reckoning is utilized in some robotic applications.[8] It is usually used to reduce the need for sensing technology, such as ultrasonic sensors, GPS, or placement of some linear and rotary encoders, in an autonomous robot, thus greatly reducing cost and complexity at the expense of performance and repeatability. 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. Dead reckoning is not totally accurate, which can lead to errors in distance estimates ranging from a few millimeters (in CNC machining) to kilometers (in UAVs), based upon the duration of the run, the speed of the robot, the length of the run, and several other factors.

Reference

  1. ^ Hu, Lingxuan; Evans, David (2004-01-01). Localization for Mobile Sensor Networks. Proceedings of the 10th Annual International Conference on Mobile Computing and Networking. MobiCom '04. New York, NY, USA: ACM. стр. 45—57. CiteSeerX 10.1.1.645.3886 Слободан приступ. ISBN 978-1-58113-868-9. doi:10.1145/1023720.1023726. 
  2. ^ Mirebrahim, Hamid; Dehghan, Mehdi (2009-09-22). Ruiz, Pedro M.; Garcia-Luna-Aceves, Jose Joaquin, ур. Monte Carlo Localization of Mobile Sensor Networks Using the Position Information of Neighbor Nodes. Lecture Notes in Computer Science. Springer Berlin Heidelberg. стр. 270—283. ISBN 978-3-642-04382-6. doi:10.1007/978-3-642-04383-3_20. 
  3. ^ Haroon Rashid, Ashok Kumar Turuk, 'Dead reckoning localisation technique for mobile wireless sensor networks', IET Wireless Sensor Systems, 2015, 5, (2), p. 87-96, DOI: 10.1049/iet-wss.2014.0043 IET Digital Library, http://digital-library.theiet.org/content/journals/10.1049/iet-wss.2014.0043
  4. ^ Turuk, Haroon (2015). „IET Digital Library: Dead reckoning localisation technique for mobile wireless sensor networks”. IET Wireless Sensor Systems. 5 (2): 87—96. arXiv:1504.06797 Слободан приступ. doi:10.1049/iet-wss.2014.0043. 
  5. ^ Gallistel. The Organization of Learning. 1990.
  6. ^ Dead reckoning (path integration) requires the hippocampal formation: evidence from spontaneous exploration and spatial learning tasks in light (allothetic) and dark (idiothetic) tests, IQ Whishaw, DJ Hines, DG Wallace, Behavioural Brain Research 127 (2001) 49 – 69
  7. ^ „Archived copy” (PDF). Архивирано из оригинала (PDF) 2006-03-13. г. Приступљено 2010-02-17. 
  8. ^ Howie M. Choset; Seth Hutchinson; Kevin M. Lynch; George Kantor; Wolfram Burgard; Lydia E. Kavraki; Sebastian Thrun (2005). Principles of Robot Motion: Theory, Algorithms, and Implementation. MIT Press. стр. 285—. ISBN 978-0-262-03327-5. 

Literatura

Spoljašnje veze

Izračunavanje koordinata na Vikimedijinoj ostavi.
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