Jump to: A B C D E F G I K L M N O P R S T U V W
- Age of corrections
- How old the latest correction message is, in seconds. If it keeps climbing, your internet link is struggling.
- Antenna height
- The straight-up distance from the ground mark to the antenna's reference point. Getting it wrong shifts every height you measure.
- ARP
- Antenna Reference Point. A specific spot on the antenna, usually the bottom of the mount, that heights are measured to.
- As-built
- A survey of what was actually built, to compare with the plans.
- Base station
- A GNSS receiver sitting still on a known spot. It figures out how wrong the satellite signals are right now and shares that as corrections.
- Baseline
- The distance between the base station and your rover. Shorter is better for accuracy.
- Carrier phase
- Measuring the satellite signal's waves themselves, not just the timing code. It's what lets RTK reach centimeter accuracy.
- Caster
- The internet server that hands out correction streams. Your rover logs in to it, like tuning into a radio station.
- Checkpoint
- A surveyed point you leave out of processing, then use to test how accurate your finished map really is.
- CMRx
- Trimble's own compact correction format. Some networks offer it for Trimble gear and machine control.
- Constellation
- One family of navigation satellites, like GPS, GLONASS, Galileo or BeiDou. More constellations means more satellites to use.
- Corrections
- Live info from a base station about how far off the satellite signals are, so your rover can cancel out the error.
- CORS
- Continuously Operating Reference Station. A permanent GPS receiver that records satellite data all day, every day.
- Data collector
- The handheld computer a surveyor uses to run the rover and store points.
- Datum
- The starting point and ruler that coordinates are measured from. The same spot has different numbers in different datums.
- DOT
- Department of Transportation. The state agency that runs many of the free state RTK networks.
- Elevation mask
- A setting that ignores satellites lower than a chosen angle above the horizon, because low signals are noisy.
- Ellipsoid
- A smooth, slightly squashed ball shape that stands in for the Earth in GPS math.
- Ellipsoid height
- Height above the smooth math shape (the ellipsoid). It's what GPS measures, and it can be very different from elevation.
- Epoch
- One moment of GPS measurement. A receiver logging at 1 Hz records one epoch every second.
- Fix
- The best RTK status. The receiver has finished its math and your position is good to a couple of centimeters.
- Float
- A middle RTK status. Corrections are coming in but the math isn't finished, so you're only good to about a foot.
- GCP
- Ground control point. A target on the ground with a surveyed position, used to line up a drone map with the real world.
- Geoid
- A lumpy, imaginary "sea level" surface around the whole Earth. Elevations are measured from it.
- GEOID18
- NOAA's model that converts GPS heights to official NAVD 88 elevations in the US.
- Geotagging
- Saving the position where each photo was taken inside the photo file.
- GGA
- A short message your rover sends with its rough location. VRS and nearest-station streams need it to know where you are.
- GNSS
- Global Navigation Satellite System. The general name for GPS (USA) and the other satellite systems like GLONASS, Galileo and BeiDou.
- GPS
- The US satellite navigation system. People often use "GPS" to mean all satellite positioning.
- Integer ambiguity
- The unknown whole number of signal waves between a satellite and your receiver. Solving it is what turns FLOAT into FIX.
- Ionosphere
- A high layer of the atmosphere charged by the sun. It slows down GPS signals and can make getting a fix harder.
- ITRF
- International Terrestrial Reference Frame. A worldwide datum. In the US it's about a meter different from NAD 83.
- Kinematic
- Measuring while moving. The "K" in RTK and PPK.
- Latency
- The delay between a correction being made and your rover getting it.
- Machine control
- GPS on bulldozers, graders or tractors that guides the blade or steering automatically.
- Mount point
- One specific correction stream on a caster, like one channel on a radio. Each one comes from a certain station or network setup.
- MSM
- Multiple Signal Messages. A newer kind of RTCM 3 message that carries all satellite systems and signals.
- Multipath
- When a satellite signal bounces off a wall, truck or water before it reaches you, like an echo. It throws off your position.
- NAD 83(2011)
- The official US datum for horizontal position right now. Most state networks give coordinates in it.
- NATRF2022
- One of the new US reference frames NOAA plans to use in place of NAD 83.
- NCN
- The NOAA CORS Network. NOAA's nationwide group of permanent base stations, with data free to download.
- NGS
- National Geodetic Survey. The part of NOAA that runs the official US coordinate system, CORS and OPUS.
- NMEA
- A common text format GPS receivers use to report position and status. GGA is one NMEA message.
- NOAA
- National Oceanic and Atmospheric Administration. The US agency that includes NGS and runs the CORS network.
- NSRS
- National Spatial Reference System. The official US system of coordinates, heights and survey marks.
- NTRIP
- The standard way RTK corrections are sent over the internet. Think of it as internet radio for correction data.
- OPUS
- Online Positioning User Service. A free NOAA website: upload a GPS file and it emails back the precise position of that spot.
- OPUS-RS
- The rapid version of OPUS for 15 minutes to 2 hours of data.
- OPUS-S
- The standard version of OPUS for 2 to 48 hours of data.
- Orbits
- The paths satellites follow. Precise orbit files tell software exactly where each satellite was.
- Orthometric height
- Height above the geoid, which is what most people call elevation or height above sea level.
- PDOP
- A score for how well spread out your satellites are. Lower is better. Satellites bunched in one part of the sky give a high, bad PDOP.
- Peak-to-peak
- In OPUS, how far apart the separate answers landed. A small number means they agree.
- Port
- A number that tells your device which "door" on the caster server to use. For NTRIP it's often 2101.
- PPK
- Post-processed kinematic. Like RTK, but the corrections are applied after the job using recorded data, so no live link is needed.
- ppm
- Parts per million. In GPS specs, 1 ppm means 1 mm of extra error for every kilometer you are from the base.
- Precision vs accuracy
- Precision means your measurements agree with each other. Accuracy means they match the true position. You want both.
- Reference frame
- A precise version of a datum, defined by real stations on the ground. ITRF2020 and NAD 83(2011) are examples.
- RINEX
- A standard file format for raw GPS data. Any brand of receiver or software can read it.
- RMS
- Root mean square. A single number that sums up how much results scatter. Smaller is better.
- Rover
- The receiver that moves around the job, like a survey pole or a drone. It uses the base's corrections to find its exact spot.
- RTCM
- The common format RTK corrections are written in, so different brands can understand each other.
- RTK
- Real-time kinematic. A way to make GPS accurate to about an inch by getting live corrections from a nearby base station.
- RTK2GO
- A free public caster where volunteers share their own base stations. Quality varies.
- RTN
- Real-time network. A group of base stations spread across an area that work together to send RTK corrections.
- Sampling rate
- How often a receiver records data, like once a second or once every 30 seconds.
- Single
- No corrections at all. Your position could be off by several meters.
- Sourcetable
- The list of every mount point a caster offers. Your app shows it when you connect without picking one.
- Stakeout
- Using a GPS rover to find and mark planned points on the ground, like where a building corner goes.
- Static survey
- Recording GPS data with the antenna sitting perfectly still for a while, which gives very precise results.
- Survey foot
- An old US foot that is slightly longer than the international foot (2 parts per million). Mixing them up causes errors over big distances.
- Survey mark
- A metal disk or rod set in the ground at a spot with a known, published position.
- Troposphere
- The lowest layer of the atmosphere, where weather happens. Water vapor in it slightly delays GPS signals.
- UFCORS
- A NOAA tool that lets you download CORS data for just the hours you need.
- VRS
- Virtual reference station. The network blends nearby stations to create a pretend base right next to you, which keeps the baseline short.
- WGS 84
- The worldwide datum GPS uses by default. It's very close to ITRF.