GNSS applications

Navigation

Automobiles may be equipped with GNSS receivers either at the factory or as aftermarket units, often displaying moving maps and information about location, speed, direction, and nearby streets and points of interest. In construction, mining, and precision agriculture, heavy equipment uses GNSS for automatic control of blades and buckets in machine guidance systems. Agricultural machinery can steer automatically or provide a visual aid on a screen for the driver, aiding controlled traffic, row crop operations, and spraying; harvesters with yield monitors can also create yield maps of paddocks. Hikers, climbers, and pedestrians in urban or rural settings can determine their position with or without separate maps, and in isolated areas the precise position can enhance rescue chances if communication with rescue workers is available. GNSS equipment is also available for the visually impaired. Boats and ships navigate all the world's lakes, seas, and oceans using GNSS, with maritime units including functions such as "man overboard" (MOB) for instantly marking a person's location overboard. GNSS may connect to self-steering gear and chartplotters via the NMEA 0183 interface, and can improve shipping traffic security by enabling AIS. Air navigation systems typically have a moving map display and are often connected to the autopilot for en-route navigation; cockpit-mounted receivers and glass cockpits appear in general aviation aircraft of all sizes, using technologies such as SBAS or DGPS to increase accuracy. Many are certified for instrument flight rules navigation, and some can be used for final approach and landing operations as in the Joint precision approach and landing system. Glider pilots use GNSS Flight Recorders to log data verifying arrival at turn points in competitions and for en route decision making during cross-country soaring.

Surveying and mapping

GNSS is used in creating maps with geographic information systems. Projects such as OpenStreetMap and TierraWiki allow users to collaboratively create maps using consumer-grade GPS receivers. High precision measurements of crustal strain can be made with differential GNSS by finding relative displacement between sensors; multiple stations around actively deforming areas like volcanoes or fault zones can determine strain and ground movement, which can then be interpreted to understand the cause of deformation, such as a dike or sill beneath an active volcano. Real-time GNSS positioning can also be part of earthquake early warning systems. When archaeologists excavate a site, they typically create a three-dimensional map detailing where each artifact is found, and high-precision GNSS simplifies this process. Most mapping grade GNSS receivers use carrier wave data from only the L1 frequency but have a precise crystal oscillator that reduces errors from receiver clock jitter, allowing positioning errors on the order of one meter or less in real-time with a differential GNSS signal received via a separate radio receiver; storing carrier phase measurements and differentially post-processing the data can yield positioning errors on the order of 10 centimeters. Survey-grade GNSS receivers can position survey markers, buildings, and road construction; these units use signals from both the L1 and L2 GPS frequencies. Although the L2 code data are encrypted, the signal's carrier wave enables correction of some ionospheric errors. These dual-frequency GPS receivers typically cost US$10,000 or more but can have positioning errors on the order of one centimeter or less when used in carrier phase differential GPS mode. The advent of L2 L5 civilian service has led to widespread production of L1/L5 and L1/L2 dual-frequency GPS devices. The survey-grade GNSS receiver industry includes a relatively small number of major players specializing in the design of complex dual-frequency receivers capable of precise tracking of carrier phases for all or most available signals to bring relative positioning accuracy down to cm-level values; the most known companies are Javad, Leica, NovAtel, Septentrio, Topcon, and Trimble.

Other uses

GNSS technology guides many precision-guided munitions, such as JDAM bombs and the Excalibur 155 mm artillery shell, to their targets. In mobile satellite communications, a directional dish on a moving vehicle like a ship or train must stay aimed at the satellite based on its current position; modern antenna controllers typically use a GNSS receiver for this. Emergency services can locate cell phones using GNSS, a capability required in the United States under E911 legislation, though not all regions have such systems. For compatible phones, GNSS depends less on the telecommunications network than radiolocation does. Assisted GPS reduces a phone's power needs and improves location accuracy. A phone's location also enables location-based services, such as advertising or other area-specific information.

Handheld GNSS receivers have spawned games like geocaching, where participants use the device to reach a specific latitude and longitude to find hidden objects left by others, often involving walking or hiking in natural settings. Another outdoor sport, geodashing, uses waypoints. Most commercial skydiving drop zones rely on GNSS to help the pilot spot the plane at the correct position so all skydivers can steer their canopies back to the landing area. In wreck diving, a scuba diving variant, GPS guides divers to the approximate location of a shipwreck on the ocean floor, which is then pinpointed with an echosounder. Many companies now sell cellular phones with GPS, allowing users to see friends on custom maps and receive alerts when someone is within a set range. These phones often combine social-networking features with standard GPS navigation, such as audible voice commands for in-car use.