Basic GPS Terminology – GPS Acronym Meaning for the Basic GPS User
GPS: Global Positioning System – A system that collects data from several stationary satellites positioned in Earth’s orbit to provide you with information for different end uses, including tracking of any object, aiding the user with navigation to any place, or to measure and map any area. What started as a system for helping US defense now extends into almost every field of life. This includes gaming (Geocache: a treasure hunt using GPS. The link takes you to an article that describes the game). Read our Bright Hub article for information on how GPS operates.
GNSS: Global Navigation Satellite Systems - A system of satellites, interlinked to provide continuous signals containing data about longitude, latitude, elevation (compared to sea-level) and time. A GNSS system also sends out other information as well, such as “ionosphere disturbance co-efficient” to enable GPS units calculate and present GPS users with better accuracy of GPS. At the moment, the only fully-functional GNSS is NAVSTAR, developed by US Defense. Other countries also have their own GNSS but they are still in the process of completion. Read our Bright Hub article for more details on GNSS.
GPS Unit: Any device capable of receiving GPS data to track your location, traffic information, help navigate to a particular place, or virtually anything involving distance and mapping. A GPS unit can be a standalone device, part of your cell phone, or incorporated into your palmtops. The main components of the GPS unit are the GPS antenna, GPS signal receiver, GPS signal processor, and finally the GPS display (OSD – On Screen Display). For more details on components of a GPS unit, click here.
1D: One Dimensional – A GPS unit that can receive data only about one of the following three: longitude, latitude, or elevation. As such, no commercial GPS unit employs 1D as the information is not enough to allow you to use your GPS unit. There is use in a research setting.
2D: Two Dimensional – A GPS unit that can receive data only about longitude and latitude. Such devices are used in areas that do not require enhanced accuracy of GPS. One example of such device is a GPS unit used to watch a stationary object for security purposes. If the object is moved, the unit triggers an alarm, announcing attempted theft of the object.
3D: Three Dimensional – GPS units capable of receiving just enough data to track any object. The three planes represent longitude, latitude, and elevation (compared to sea-level). However, the data is not as accurate while moving because it takes time for the signal to reach the GPS unit. If it is moving, the data your unit gets may be a few inches/miles behind depending upon the speed at which the GPS unit is moving.
4D: Four Dimensional – The most common (commercial) GPS units used as GPS technology. These commercially available devices can receive the time of signal along with the data received under 3D. The satellite sending the 3D data includes a time-stamp on the signal so that your unit can offer precise information for almost any purpose: tracking moving objects, navigation, and mapping.
L1, L2, and L2C: The frequencies on which, the GPS system sends data to GPS units. The L1 frequency is for civilians while L2 is reserved for defense only. The L2 frequency employs high encryption in addition to extra information to compute enhanced accuracy of GPS. As the need for precise calculations picked up in different fields of science, the US Defense system allowed a part of L2 signal for civilians (L2C). Most of the commercial GPS units are now using L2C for operations for reducing GPS error possibilities and increasing the accuracy of GPS. General L1 frequency offers two types of signals: C/A Code and P Code Signals.
The C/A (Coarse Acquisition Code) is slightly less strong than the P Code (Precision Code). The commercial GPS units in the market may use both C/A and P Codes to check the difference in measurements and thereby offer you enhanced precision of GPS. The difference in C/A and P Code can be further understood upon studying this summary.
L1C (enhanced L1 signal code for civilians) is yet another signal type in the works and is due in 2013. The L1C is the brainchild of GALILEO, the European GNSS. Codes for processing GPS signals are developed by GPS vendors and this determines the cost of the GPS units.
The next page deals with GPS acronym meanings encountered in the GPS technology ads that mention accuracy of GPS and GPS safety standards.
GPS Acronym Meanings – Advanced GPS Terminology
AS – Anti-Spoofing – A method to counter GPS spoofing**. GPS Spoofing** refers to fake satellite data or intentional manipulation of the original data to fool GPS units**.** Some people do this for fun, and the US Defense implements a somewhat similar process: S/A or SA – Selective Availability. The US Defense system makes some changes to data accessible by civilian GPS units for security reasons. Selective Availability was discontinued some years back when the civilian GPS units began to fill niches in fields that required precise data. Even now, people or technical errors can cause disturbances in the signal thereby altering the data. To check out how to deal with weak signals or manipulated signals, click here. If an ad displays SAASM - Selective Availability and Anti-Spoofing Module, it means that the GPS receiver has some code that can bypass both spoofing and SA.
AJ – Anti Jamming – A technology that employs methods to bypass GPS jammers installed in a building or area for continuous blocking of reception of GPS signals. An example of a GPS jammer is cell phone jammers installed in some institutions. These may stop GPS signals reaching the GPS unit in your cell phone. A GPS unit carrying an AJ will function even if such jammers are installed in the campus where you are trying to use your GPS unit.
Security and Performance Abbreviations
CE Approval (Conformity Mark) is the security standard used in Europe for digital devices to certify the product is safe for use. It is similar to EnergyStar, which indicates that the product consumes less power. You may encounter the term, “approved by FCC”. FCC (Federal Communications Commission) is the US based regulatory commission for testing electronics for safety and other possible issues. Similarly ISO (International Standards Organization) is yet another organization that tests a GPS unit under different conditions and approves it only if it passes the tests. These are the major safety and performance standards accepted across the planet.
Error Possibilities in GPS
Every GPS unit is prone to error computing its exact position. There are a few methods that help you understand the probability of error. This information helps you decide how much to depend on the information displayed on the OSD (On Screen Display - The Display Screen of your GPS unit). The following paragraphs discuss some of the popular error GPS terminology and the acronym meanings.
CEP: Circular Error Probability – In easy words, if the GPS info says that the GPS handheld carries a CEP of 10 meters, chances are 50 percent the time the measurement falls within a circle of radius 10m, where the center of the circle is your GPS receiver. So, there is a 50 percent chance that the measurement is outside the same circle.
95 Percentile: Also called 95 percent confidence, this method offers a 5 percent probability that the measurement is other than what is displayed on the GPS unit. For example, if the measurement is 10 meters, there is a 95 percent chance the measurement will be somewhere in a circle of 10 meter radius and a 5 percent possibility the difference is more than 10 meters.
DRMS: Distance Root Mean Square – This theorem offers 64 percent probability of error from the measurement on your GPS display. Similarly, 2DRMS (twice DRMS) offers an error probability of 98 percent within the display and 2 percent more probability of the error. For a GPS claiming 10 meters accuracy, the DRMS probability of error is 64 per cent within the 10 meters’ circle while 2DRMS error probability is 98 per cent within the 10 meter circle with only 2 per cent possibility of the error being above 10 meters.
NOTE: These Error Possibilities in GPS are only probabilities and not absolute errors. Depending on the GPS, you can find one that offers least error probabilities, such as the 95 percentile.
The next page deals with the common measurement symbols used in GPS acronyms and also GPS terminology about some of the most popular GPS augmentation methods.
GPS Technology – GPS Accuracy Measurement Units
Bps - Bits per second
dB – Decibel
dBW - Decibels per watt
DEG – Degree
FPM - Feet per Minute (used to determine the speed of a data signal within the earth’s atmosphere)
Gbps - Gigabits per Second
GHz – Gigahertz
GW - Gross Weight (Generally, refers to the overall weight of the GPS device)
KT - (kts) – Knots (Meant for GPS in Oceanography and GPS for Coast Guards). A knot is a measurement used with ships, submarines, and boats. Ancient voyagers used a rope with knots at equal distances to measure the distance while traveling. Though the technology has changed since that era, the term is still used for measuring distance when you refer to water transport.
GPS Acronym meanings - Enhancements to GPS Technology
DGPS – Differential GPS – This method is used to enhance the precision of GPS units. The process involves collecting data from satellites as well as from ground based GPS stations. Once the unit receives the data, it computes both separately and checks for the difference. The system then broadcasts this difference over radio waves so GPS units can correct their measurements. As of now, Australia uses two such systems for marine navigation as well as for land survey and navigation on land. The US employs this technique for the Coast Guard.
SBAS – Satellite based Augmentation System: The system employs several data signals to achieve the best possible accuracy of GPS. The SBAS receives additional data from one or more satellites along with data from Ground Based GPS Stations. It then takes into account the different factors affecting GPS signals from satellites (for example: ionosphere friction, problems with dust in space, and other disturbances) to compute and calculate the difference. Once the difference is established, it is sent back to the satellites. Based upon the data sent back to the satellites, the GNSS adjusts the measurements and broadcasts the signals back to earth – offering enhanced precision in your GPS receiver.
GBAS – Ground Based Augmentation System: The system works in the same way as SBAS, with the difference that the signals are directly broadcast to end-users instead of sending them back to satellites for correction. A GBAS does not offer much coverage and is effective in a range of 20 to 25km.
GPS technology is rapidly improving and finding uses in almost every field of terrain based science. With this, references on GPS terminology will keep on adding GPS acronyms as they are created. Thus, a GPS glossary can never be completely comprehensive. This article explains current general GPS terminology, for use as a ready reference to common GPS acronyms. It will be updated regularly.