GPS Terminology

Here are some of the most common words that you will come across while reading any article in any website related to GPS. These will provide you basic idea of its functions and how GPS deals with these things.

Way Point – These are a set of coordinates representing some important places of the route, which can be stored on the GPS unit. One can determine the coordinates with the help of a map and compass and store them by giving some unique name. Not necessarily the way points represents any physical structure and even one can mark a waypoint at sea and in air. Marking these waypoints helps in returning to the same place without wondering hither. One can also mark the waypoints in respect to another that’s been already stored and entering the distance and compassing bearing to the new place.

Bearing – Bearing denotes the direction of the route, after you enter the coordinates of your actual destination; GPS calculates the direction of each point you want to cover. So bearing is the direction of the next waypoint stored in your GPS receiver.

Heading – Heading represents the direction that one actually wants to go irrespective of the direction of the bearing or each waypoint. This is because sometimes you can't go directly to the destination due to natural or any other reasons that forces you in following a zigzag path. So it is the ultimate direction of the place from your base point.

Route – Route is created by the combination of a number of waypoints and so it is important for the receiver to store coordinates of certain places for setting a route. A route should be in the direction that one wants to travel. So you can prepare your own route by marking the waypoints in the order you want to cover. On the basis of which GPS guides you to your destinations. By taking help of a digital map you can determine the coordinates of the route and later taking help of software those can be entered in the GPS system.

Route Leg – It is the straight-line between two adjacent waypoints in a route.

Course - represents the direction from the starting point to the destinations and is determined through angular measurements like degrees, radians or mils. Also can be termed as the direction from one waypoint to the next one in a route.

WAAS – The word stands for Wide Area Augmentation System in which the satellites and ground station observation are taken into account for correcting GPS signals for better accuracy. In this system, differential signals are sent back to satellites from ground stations for improving accuracy. Use of this system improves the signal accuracy up to five times with an average of 3 meter where as GPS without WAAS system can leave a difference of 5 to 15 meters.

Track – It is the direction that one moves and not similar as heading that describes the ultimate direction or the direction of the destination. In case of land navigation it can be referred as heading but in sea and air one can follow different direction. So track implies the direction of movement irrespective of the heading one.

Track Log – Track log in a GPS unit records the coordinates of the waypoints automatically with time to its memory, which can be seen on the maps of your receiver. So its better to keep your track log button on while moving from one place to another.

TrackBack – Track log is the feature in the GPS unit that automatically stores the coordinates of the waypoints and TrackBack is another feature that converts a track log into a route. For example if track log has stored around 100 waypoints then track back selects around 30 convenient waypoints and make the most easy route to direct you back to base point. So this is really helpful in case of a very long travel route where it is difficult to make the shortest route to your way back.

8 or 12Channel Receiver – A 8 channel receiver is capable of marking 8 satellites at any point of time where as a 12 channel receiver can receive signals from 12 different satellites and then evaluates its own position. So it is obvious that 12 channel is more accurate about positioning and timing.

TTFF – TTFF stands for ‘time to first fix’ and represents the time period that one GPS receiver takes to calculate a single position immediately after its turn on.

Transducer – It’s an electro-mechanical device responsible for transfiguring one form of energy to another. For example, GPS fish finder uses this to separate signals and enhance the data to show underwater object.

Triangulation – Triangulation is the process of determining coordinates and distance of a point by calculating the length of one side of a triangle in respect to the measurement of angles and two other reference points by applying the laws of trigonometry.

Selective Availability – It is the intentional error added to the accuracy of GPS signals by US Department of Defense in order to restrict or check the maximum accuracy to the hostile and terrorist organization.

P Code – The Precise or Protected code is the binary bi-phase shift modulated of the L1 and L2 frequencies. This is generally used by the US Defense Department by encrypting the code to Y-Code. Each satellite has unique P-Code that distinguishes it from others.

Y-Code – The result of Anti-Spoofing (AS) that converts the P-code to Y-code and is generally carried out by DoD of United States and other authorized party.

Ephemeris Data - Ephemeride means orbits and ephemeris data are the data containing current orbital positions of satellites. So, it’s not constant and changes after time by time.

Differential GPS (DGPS) – Differential Global Positioning System (DGPS) is the process that improves the accuracy of GPS signals. By this method a number of ground based navigation stations first receives the signals and take the readings on a known point. The difference between the known location and the GPS readings is the differential. It is being used to calculate the correct data from the Selective Availability where correct measurement is necessary.

Pseudo Range – Is the approximate distance between the GPS receiver antenna and satellite. This is in fact the satellite propagation time between the satellite and receiver while transmitting signals but termed as distance.

Acquisition Time – Time taken by a GPS receiver in acquiring satellite signals and determining its initial position.

Active Antenna – These are the antennas situated in different parts of earth and are responsible for amplifying GPS signals before sending it directly to the GPS receiver.

Almanac Data – Consists of orbital information and status of every satellite in the GPS constellation. This allows GPS receivers to locate satellites quickly and determining its own position.

Altimeter – This is a device to calculate altitude or elevation of different points. A barometer is also used as an altimeter in aircraft that measures the pressure changes in different areas and on the basis of which the altitudes also changes.

Atomic Clock – It uses atomic resonance frequency standard to calculate the real time. These play a vital role in the navigation technology while measuring accurate time. The operation of these clocks depends on the use of cesium and rubidium frequency standards.

Base map – Today GPS units are equipped with maps that include physical and political geography of a place with ocean, rivers, lakes and some prominent cities, towns, airport, rail, roads etc. Base map is varied from place to place and companies are providing this according to the needs of the customer.

Beacon – These are land based radio stations usually transmits signals from a particular radio frequency.

C/A Code – Coarse Acquisition/Clear Acquisition Code is the basic positioning signals that GPS receiver uses to fix its position and time.