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Writer's pictureAntonio Liska

The GPS Surveying Glossary

Updated: Oct 17, 2024

Aerotriangulation

Aerotriangulation is a photogrammetric method of determining the geometric properties of objects from photographic images, especially for mapping and modeling purposes.

Antenna Phase Center

The point in an antenna where the GNSS signal is considered to be received, crucial for precise positioning calculations.

Base Station

A Base Station is a GNSS antenna and receiver set up as a reference specifically to collect data to be used in determining precise rover positions.

Baseline

In GNSS surveying, the vector distance between two GNSS receivers simultaneously tracking the same satellites.

BeiDou

A global navigation satellite system developed and operated by China, providing positioning, navigation, and timing services.

BIM

Building Information Modeling is a process involving the generation and management of digital representations of the physical characteristics of sites.

BIMs

Building Information Models are digital models that support decision-making regarding a built asset.

CAD

Computer-Aided Design is the use of computers in the creation, modification, analysis, or optimization of a design, typically used in reference to 3D modeling of physical objects.

Cloud Point

A set of data points in space produced by 3D scanners or photogrammetry, representing the external surface of an object or terrain.

Control Point

A point on the ground with known coordinates used to georeference and align spatial data accurately.

CORS

Continuously Operating Reference Stations are networks of GNSS receivers that provide real-time correction data and support high-accuracy positioning.

DEM

A Digital Elevation Model is a 3D representation of a terrain's surface created from terrain elevation data, excluding objects like buildings and vegetation.

DOP (Dilution of Precision)

An indicator of the quality of a GNSS position considering the geometry of the satellite constellation relative to the GNSS receiver. A low DOP value is preferred. Common DOP types are:

  • GDOP - Geometric Dilution of Precision considers the combination of vertical, horizontal, time, and position errors.

  • HDOP - Horizontal Dilution of Precision represents the effect of satellite geometry on horizontal position accuracy.

  • PDOP - Position Dilution of Precision combines the horizontal and vertical DOP.

  • RDOP - Relative Dilution of Precision measures the relative positional error between two receivers.

  • TDOP - Time Dilution of Precision represents the effect of satellite geometry on time determination accuracy.

  • VDOP - Vertical Dilution of Precision represents the effect of satellite geometry on vertical position accuracy.

DSM

A Digital Surface Model is a 3D representation of the Earth's surface, including all objects on it, such as buildings, trees, and other structures.

DTM

A Digital Terrain Model is similar to a DEM but includes additional terrain attributes, such as break lines and mass points, to represent the ground surface more accurately.

ECEF

Earth-Centered, Earth-Fixed is a Cartesian coordinate system used by the WGS‑84 reference frame. In this coordinate system, the origin is at the Earth's center of mass.

EGNOS

European Geostationary Navigation Overlay Service is a regional satellite-based augmentation system that improves the accuracy of GNSS signals over Europe.

Ellipsoid

A mathematically defined surface that approximates the shape of the Earth, used as a reference in geodesy and map projections.

Ephemeris Data

Information about the positions and velocities of GNSS satellites, used by receivers to calculate accurate positions.

Fixed Solution

Indicates that the integer ambiguities have been resolved, providing the most precise type of solution available in an RTK GPS application.

Float Solution

Indicates that the integer ambiguities have not been resolved, resulting in positional accuracy less than that of a fixed solution.

Galileo

A global navigation satellite system controlled by the European Union.

GCP (Ground Control Point)

An easily identifiable point on the ground that can be used as a reference for measurements. Ground control points are often used in surveying and photogrammetry to provide a known reference point.

Geocoding

The process of converting addresses or other location descriptors into geographic coordinates.

Geodatabase

A database designed to store, query, and manipulate geographic information and spatial data.

Geodetic Datum

A coordinate system and reference points used to locate places on the Earth, serving as a foundation for mapping and surveying.

Geoid

The hypothetical shape of the Earth, coinciding with mean sea level, used as a reference surface from which to measure elevations.

Georeferencing

The process of assigning real-world coordinates to each pixel of a raster image or vector dataset, aligning spatial data to a known coordinate system.

GIS

A Geographic Information System is a system that collects, stores, analyzes, and displays geographically referenced information.

GLONASS

Global Navigation Satellite System is the GNSS controlled by the Russian government.

GNSS

Global Navigation Satellite System is the standard generic term for satellite navigation systems that provide geospatial positioning with global coverage.

GPS

Global Positioning System is the GNSS controlled by the U.S. government.

GSD

Ground Sampling Distance is the distance between pixel centers measured on the ground, representing the spatial resolution of an aerial image.

HDOP

Horizontal Dilution of Precision represents the effect of satellite geometry on horizontal position accuracy.

IMU

An Inertial Measurement Unit is a device that measures and reports a body's specific force, angular rate, and sometimes the magnetic field surrounding the body, using a combination of accelerometers and gyroscopes.

Kinematic Surveying

A method of surveying where the GNSS receiver is in motion, allowing for rapid data collection over large areas.

L1

The primary L‑band carrier used by GNSS satellites to transmit satellite data on the 1575.42 MHz frequency.

L2

The secondary L‑band carrier used by GNSS satellites to transmit satellite data on the 1227.6 MHz frequency.

LiDAR

Light Detection and Ranging is a remote sensing method that uses laser pulses to measure distances to the Earth's surface, generating precise, three-dimensional information about the shape of the Earth and its surface characteristics.

Map Projection

A systematic transformation of latitudes and longitudes from the Earth's curved surface onto a flat plane.

Multipath

An error in GNSS signal reception caused by signals reflecting off surfaces before reaching the receiver, leading to inaccuracies.

NAD83

North American Datum 1983 is a geocentric datum and reference system used for geodetic control in North America.

NMEA

The National Marine Electronics Association defines a standard data format for interfacing marine electronic devices, commonly used by GNSS receivers to transmit data.

NTRIP

Networked Transport of RTCM via Internet Protocol is a standard method for RTK GPS rovers and base stations to exchange correction data over the internet.

OPUS

Online Positioning User Service provides free post-processing of GPS base data into high-accuracy National Spatial Reference System coordinates.

Orthomosaic

An orthomosaic is a geometrically corrected and georeferenced aerial image composed of multiple photographs stitched together to create a seamless and accurate map.

PDOP

Position Dilution of Precision combines the effects of HDOP and VDOP to represent the effect of satellite geometry on three-dimensional position accuracy.

Photogrammetric Tie Point

Points identified on overlapping images used to stitch images together in photogrammetry, ensuring accurate alignment.

Photogrammetry

The science of making measurements from photographs, especially for recovering the exact positions of surface points.

PPK

Post-Processed Kinematic is a GPS correction technique where the correction calculations are performed after data collection, rather than in real-time like RTK.

PPP

Precise Point Positioning is a GNSS data processing technique that provides highly accurate position solutions without the need for a local reference station.

Precision

A measure of how closely repeated measurements or observations under unchanged conditions show the same results, indicating the repeatability of one or a set of measurements.

RDOP

Relative Dilution of Precision measures the relative positional error between two receivers.

RINEX

Receiver Independent Exchange Format is a file format that is commonly used to interchange raw satellite navigation system data.

Rover

In GNSS surveying, a mobile receiver unit that collects data while moving, receiving corrections from a base station or network.

RTCM

Radio Technical Commission for Maritime Services defines the RTCM protocol that high-precision GPS receivers use to exchange correction data.

RTK

Real-Time Kinematic is a technique that uses carrier-based ranging to provide ranges to satellites that are much more precise than those available through code-based positioning.

RTN

Real-Time Network is a network of GNSS reference stations that provide real-time corrections over a wide area, enhancing positioning accuracy for rovers.

Satellite Observation

A recording of satellite signals made using GNSS receivers for later processing.

SBAS

Satellite-Based Augmentation System enhances GNSS signals by providing correction messages, improving accuracy, integrity, and availability.

SBET

Smoothed Best Estimate of Trajectory is data output from inertial measurement units (IMUs) combined with GNSS data to provide accurate position and orientation information.

SfM

Structure from Motion is a photogrammetric technique that reconstructs 3D structures from 2D image sequences by estimating camera positions and orientations.

SNR

Signal-to-Noise Ratio is a measure of signal strength relative to background noise, important in assessing the quality of GNSS signals.

Static Surveying

A surveying technique where the GNSS receiver remains stationary for a period, providing high-precision position data.

TDOP

Time Dilution of Precision represents the effect of satellite geometry on time determination accuracy.

Transformation

The mathematical process of converting coordinates from one coordinate system to another.

Tropospheric Delay

The slowing of GNSS signals as they pass through the Earth's troposphere, causing delays that can affect positioning accuracy.

UAV

An Unmanned Aerial Vehicle is an aircraft without a human pilot onboard. In surveying and mapping, UAVs are often used to collect aerial imagery and data for analysis.

UTM

Universal Transverse Mercator is a coordinate system that divides the world into a series of six-degree longitudinal zones, allowing for detailed mapping.

VDOP

Vertical Dilution of Precision represents the effect of satellite geometry on vertical position accuracy.

WGS‑84

World Geodetic System 1984 is the mathematical ellipsoid used by GPS since January 1987.

WMS

Web Map Service is a standard protocol for serving georeferenced map images over the internet.


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