Editing Compass (section)

== Non-magnetic compasses ==

There are other ways to find north than the use of magnetism, and from a navigational point of view a total of seven possible ways exist<ref name="JournalOfNavigation2016" /> (where magnetism is one of the seven). Two sensors that use two of the remaining six principles are often also called compasses, i.e. the gyrocompass and GPS-compass.

A [[gyrocompass]] is similar to a [[gyroscope]]. It is a non-magnetic compass that finds [[true north]] by using an (electrically powered) fast-spinning wheel and friction forces in order to exploit the rotation of the Earth. Gyrocompasses are widely used on [[ship]]s. They have two main advantages over magnetic compasses:
* they find ''[[true north]]'', i.e., the direction of [[Earth]]'s rotational axis, as opposed to [[Magnetic North Pole#Magnetic north and magnetic declination|magnetic north]],
* they are not affected by [[ferromagnetic]] metal (including iron, steel, cobalt, nickel, and various alloys) in a ship's hull. (No compass is affected by nonferromagnetic metal, although a magnetic compass will be affected by any kind of wires with [[electric current]] passing through them.)

Large ships typically rely on a gyrocompass, using the magnetic compass only as a backup. Increasingly, electronic [[fluxgate compass]]es are used on smaller vessels. However, magnetic compasses are still widely in use as they can be small, use simple reliable technology, are comparatively cheap, are often easier to use than [[GPS]], require no energy supply, and unlike GPS, are not affected by objects, e.g. trees, that can block the reception of electronic signals.

[[GPS receiver]]s using two or more antennae mounted separately and blending the data with an inertial motion unit (IMU) can now achieve 0.02° in heading accuracy and have startup times in seconds rather than hours for gyrocompass systems. The devices accurately determine the positions (latitudes, longitudes and altitude) of the antennae on the Earth, from which the cardinal directions can be calculated. Manufactured primarily for maritime and aviation applications, they can also detect pitch and roll of ships. Small, portable GPS receivers with only a single antenna can also determine directions if they are being moved, even if only at walking pace. By accurately determining its position on the Earth at times a few seconds apart, the device can calculate its speed and the true bearing (relative to ''[[true north]]'') of its direction of motion. Frequently, it is preferable to measure the direction in which a vehicle is actually moving, rather than its heading, i.e. the direction in which its nose is pointing. These directions may be different if there is a crosswind or tidal current.

GPS compasses share the main advantages of gyrocompasses. They determine true North,<ref name="JournalOfNavigation2016">{{cite journal |last= Gade |first= Kenneth |year= 2016 |title= The Seven Ways to Find Heading |journal= The Journal of Navigation |volume= 69 |issue= 5 |pages=955–970 |url=http://www.navlab.net/Publications/The_Seven_Ways_to_Find_Heading.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.navlab.net/Publications/The_Seven_Ways_to_Find_Heading.pdf |archive-date=2022-10-09 |url-status=live |doi= 10.1017/S0373463316000096 |bibcode= 2016JNav...69..955G |s2cid= 53587934 }}</ref> as opposed to magnetic North, and they are unaffected by perturbations of the Earth's magnetic field. Additionally, compared with gyrocompasses, they are much cheaper, they work better in polar regions, they are less prone to be affected by mechanical vibration, and they can be initialized far more quickly. However, they depend on the functioning of, and communication with, the GPS satellites, which might be disrupted by an electronic attack or by the effects of a severe solar storm. Gyrocompasses remain in use for military purposes (especially in submarines, where magnetic and GPS compasses are useless), but have been largely superseded by GPS compasses, with magnetic backups, in civilian contexts.