Glossary
This topic explains some of the terms used in this Help.
| accuracy | The closeness of a measurement or coordinate value to the actual (true) or accepted value. |
| alignment |
Alignments can be defined in the General Survey or Roads software. Alignments are stored as RXL files and can be easily shared between jobs and with other controllers. Alignments defined in General Survey always have a horizontal component that consists of straight lines, and optionally circular arcs. A vertical component is optional and consists of grades between points. Alignments defined in the Roads software can include transitions in the horizontal component and parabolic and/or circular vertical curves at changes of grade in the vertical component. In Roads you can also add templates or superelevation and widening records to define additional road elements. When used with respect to road design, the horizontal alignment defines the centerline. The vertical alignment is often referred to as the profile. When creating or editing an alignment in the Roads software, you can add templates and superelevation and widening records to define additional road elements and then stake them. If an RXL file contains these additional elements, they appear in the map in General Survey but cannot be staked from the General Survey Stakeout menu. You must use the Roads Stakeout menu to stake out elements other than the horizontal or vertical alignment. |
| almanac | Data, transmitted by a GNSS satellite, that includes orbit information on all the satellites, clock correction, and atmospheric delay parameters. The almanac facilitates rapid satellite acquisition. The orbit information is a subset of the ephemeris data with reduced precision. |
| Angles and distance | Measurement of horizontal and vertical angles and a slope distance. |
| Angles only | Measurement of horizontal and vertical angles. |
| annotation | Markings on images for the purpose of clarification. |
| Anti‑Spoofing (AS) | A feature that allows the U.S. Department of Defense to transmit an encrypted Y‑code in place of P‑code. Y‑code is intended to be useful only to authorized (primarily military) users. Anti‑Spoofing is used with Selective Availability to deny the full precision of GNSS to civilian users. |
| attribute | A characteristic or property of a feature in a database. All features have a geographic position as an attribute. Other attributes depend on the type of feature. For example, a road has a name or designation number, surface type, width, number of lanes, and so on. Each attribute has a range of possible values, called a domain. The value chosen to describe a particular feature is called the attribute value. |
| Autolock | The ability to lock onto and track a target. |
| automated rounds | The process of automatically measuring a multiple observations to observed points. |
| autonomous positioning | The least precise form of positioning that a GNSS receiver can produce. The position fix is calculated by one receiver from satellite data alone. |
| azimuth | Horizontal direction relative to a defined coordinate system. |
| Backsight | Point with known coordinates or known azimuth from the instrument point that is used to orientate the instrument during station setup. |
| base station | In a GNSS survey, you observe and compute baselines (the position of one receiver relative to another). The base station acts as the position from which all unknown positions are derived. A base station is an antenna and receiver set up on a known location specifically to collect data to be used in differentially correcting rover files. |
| baud | A unit of data transfer speed (from one binary digital device to another) used in describing serial communications; generally one bit per second. |
| BIM | Building Information Modeling (BIM) is a process where the planning, design, construction, and maintenance of buildings and other built assets such as roads, bridges or utilities infrastructure is managed using digital 3D models. BIM file formats supported in Trimble Access are IFC and DXF. |
| C/A (Coarse Acquisition) code | A pseudorandom noise (PRN) code modulated onto an L1 signal. This code helps the receiver compute the distance from the satellite. |
| change face | Refers to when the face of the conventional instrument that is measuring observations changes between face 1 and face 2. On a servo instrument, this happens automatically. On a robotic instrument, this happens when you tap Change face in the Trimble Access software. On a mechanical instrument, you must manually change face on the instrument. |
| CMR | Compact Measurement Record. A satellite measurement message that is broadcast by the base receiver and used by RTK surveys to calculate an accurate baseline vector from the base to the rover. |
| constellation | A specific set of satellites used in calculating positions: three satellites for 2D fixes, four satellites for 3D fixes. All satellites visible to a GNSS receiver at one time. The optimum constellation is the constellation with the lowest PDOP. See also PDOP. |
| construction offsets | A specified horizontal and/or vertical offset distance to enable equipment to operate without disturbing construction stakes. |
| Construction point | A point that is measured using the "quick fix" option in COGO. |
| control point | A point on the earth that has an accurately known geographic position. |
| conventional survey | In a conventional survey, the controller is connected to a conventional survey instrument such as a total station. |
| curvature and refraction | Correction to the measured vertical angle for the curvature of the earth and the refraction caused by the earth's atmosphere. |
| data message | A message, included in the GNSS signal, that reports on the location and health of the satellites as well as any clock correction. It includes information about the health of other satellites as well as their approximate position. |
| datum | See geodetic datum. |
| design code | The code name given to the design point. |
| design name | The name given to the design point. |
| Differential Positioning | Precise measurement of the relative position of two receivers tracking the same satellites simultaneously. |
| Direct Reflex (DR) | Type of EDM that can measure to non reflective targets. |
| DOP (Dilution of Precision) | An indicator of the quality of a GNSS position. DOP takes into account the location of each satellite relative to other satellites in the constellation, as well as their geometry relative to the GNSS receiver. A low DOP value indicates a higher probability of accuracy. Standard DOPs for GNSS applications are: – PDOP – Position (three coordinates) – GDOP – Geometric (three coordinates and time) – RDOP – Relative (Position, averaged over time) – HDOP – Horizontal (two horizontal coordinates) – VDOP – Vertical (height only) – TDOP – Time (clock offset only) |
| Doppler shift | The apparent change in frequency of a signal caused by the relative motion of satellites and the receiver. |
| DTM | Digital Terrain Model. A digital representation of the shape of a surface in three dimensions. The represented surface may be an existing terrain, proposed grade surfaces, or a combination of both. Types of DTM include A triangulated irregular network (TIN) is a type of DTM. |
| dual‑frequency | GNSS receiver that uses both L1 and L2 signals from GNSS satellites. A dual‑frequency receiver can compute more precise position fixes over longer distances and under more adverse conditions because it compensates for ionospheric delays. |
| Dual‑prism offset | Measurement of horizontal and vertical angles and a slope distance to two prisms located on one prism pole for the purpose of positioning an obstructed point. |
| Earth‑Centered, Earth‑Fixed (ECEF) | A cartesian coordinate system used by the WGS‑84 reference frame. In this coordinate system, the center of the system is at the earth's center of mass. The z axis is coincident with the mean rotational axis of the earth and the x axis passes through 0° N and 0° E. The y axis is perpendicular to the plane of the x and z axes. |
| eccentric object | Measurement of horizontal and vertical angles and a slope distance to the face of a radial object (for example, power pole). An additional horizontal angle is observed to the side of the object to calculate the radius and thus position the center of the object. |
| EGNOS | European Geostationary Navigation Overlay Service . A satellite‑based augmentation system (SBAS) that provides a free‑to‑air differential correction service for GNSS. |
| elevation | Height above mean sea level. Vertical distance above the geoid. |
| elevation mask | The angle below which Trimble recommends that you do not track satellites. Normally set to 10 degrees to avoid interference from buildings and trees as well as ground multipath errors. |
| ellipsoid | A mathematical model of the earth formed by rotating an ellipse around its minor axis. |
| ephemeris | The current satellite position predictions, transmitted in the data message. |
| epoch | The measurement interval of a GNSS receiver. The epoch varies according to the survey type: – for real‑time surveys it is set at one second – for postprocessed surveys it can be set to a rate of between one second and one minute |
| face 1 | Observing position of an instrument where the vertical circle is commonly on the left hand side of the telescope. |
| face 2 | Observing position of an instrument where the vertical circle is commonly on the right hand side of the telescope. |
| FastStatic survey | A type of GNSS survey. A FastStatic survey is a postprocessed survey using occupations of up to 20 minutes to collect raw GNSS data. The data is postprocessed to achieve subcentimeter precisions. |
| feature |
A representation of a real‑world object on a map. Features can be represented as points, lines, or polygons. Multipoint features consist of more than one point but only reference one set of attributes in the database. |
| feature codes | Simple descriptive words or abbreviations that describe the features of a point. For more information, refer to the Help |
| fixed solution | Indicates that the integer ambiguities have been resolved and a survey is initialized. This is the most precise type of solution. |
| float solution | Indicates that the integer ambiguities have not been resolved, and that the survey is not initialized. |
| FSTD (fast standard) | The method of measuring one distance and one angle to coordinate a point. |
| GAGAN | GPS Aided Geo Augmented Navigation. A regional satellite‑based augmentation system (SBAS) currently in development in India. |
| Galileo | Galileo is a global navigation satellite system (GNSS) built by the European Union (EU) and European Space Agency (ESA). Galileo is an alternative and complementary GNSS to the U.S. Global Positioning System (GPS), the Russian GLONASS, and the Japanese Quasi‑Zenith Satellite (QZSS). |
| GDOP | Geometric Dilution of Precision. The relationship between errors in user position and time, and errors in satellite range. See also DOP . |
| GENIO | GENeric Input Output file exported by a number of road design software packages that defines a road as a series of strings. See also String. |
| geodetic datum | A mathematical model designed to fit part or all of the geoid (the physical earth's surface). |
| geoid | The surface of gravitational equipotential that closely approximates mean sea level. |
| GLONASS | GLObal NAvigation Satellite System (GLONASS) is the global navigation satellite system (GNSS) operated for the Russian government by the Russian Space Forces. GLONASS is an alternative and complementary GNSS to the U.S. Global Positioning System (GPS), the European Union Galileo positioning system, and the Japanese Quasi‑Zenith Satellite (QZSS). |
| GNSS | Global Navigation Satellite System (GNSS). This is the standard generic term for satellite navigation systems that provide geospatial positioning with global coverage. |
| GNSS survey | In a GNSS survey, the controller is connected to a GNSS receiver. |
| GPS | Global Positioning System (GPS) is the global navigation satellite system (GNSS) operated U.S. government. GPS is an alternative and complementary GNSS to the GLObal NAvigation Satellite System (GLONASS), the European Union Galileo positioning system, and the Japanese Quasi‑Zenith Satellite (QZSS). |
| GPS time | A measure of time used by the NAVSTAR GPS system. |
| H. Angle offset | Measurement of vertical angle and slope distance. Horizontal angle is then measured separately, usually to an obstructed point. |
| H. Angle only | Measurement of horizontal angle. |
| HDOP | Horizontal Dilution of Precision. See also DOP. |
| Helmert adjustment | A Helmert transformation is a coordinate transformation which uses rotation, scaling, and translation. The horizontal adjustment in a GNSS site calibration is a 2D form of Helmert transformation, and it can also be used for computing a resection. |
| high dynamic range (HDR) |
With high dynamic range turned on, multiple images are captured, each with different exposure settings, each time the camera button is pressed. During HDR processing the images are combined to produce a composite image that has better tonal range and can therefore show more detail than any of the individual images. For images captured using a:
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| horizontal circle | Graduated or digital disc from which the horizontal angle is measured |
| IFC files | IFC (.ifc) files are Industry Foundation Class files. They contain BIM models that can be used for surveying fieldwork including stakeout and cogo calculations. |
| imaging rover | A mobile device containing a camera that is used to capture images. It may contain a GNSS receiver or it may connect to a GNSS receiver or attach to a prism to record its location each time images are captured. |
| instrument height | Height of the instrument above the instrument point. |
| instrument point | Point that the instrument is occupying. |
| integer ambiguity | The whole number of cycles in a carrier phase pseudorange between the GNSS satellite and the GNSS receiver. |
| integrated survey | In an integrated survey, the controller is connected to both a conventional survey instrument and a GNSS receiver at the same time. The Trimble Access software can quickly switch between the two instruments, within the same job. |
| ionosphere | The band of charged particles 80 to 120 miles above the earth's surface. The ionosphere affects the accuracy of GNSS measurements if you measure long baselines using single‑frequency receivers. |
| K factor | The K factor is a constant defining a vertical curve in a road definition. K = L/A. where: L is the length of the curve A is the algebraic difference between the incoming and outgoing slopes in % |
| L1 | The primary L‑band carrier used by GNSS satellites to transmit satellite data. |
| L2 | The secondary L‑band carrier used by GNSS satellites to transmit satellite data. Block IIR‑M and later GPS satellites will transmit an additional signal on L2 called L2C. |
| L5 | The third L‑band carrier used by GNSS satellites to transmit satellite data. This has been added to Block IIF and later GPS satellites. |
| measurement modes: Standard (STD), Fast Standard (FSTD), Tracking (TRK) | Angles are measured and averaged as one distances is measured. STD mode is indicated by an S next to the instrument icon on the status bar. One angle and one distance are measured. FSTD mode is indicated by an F next to the instrument icon on the status bar. Angles and distances are continually measured. TRK mode is indicated by a T next to the instrument icon on the status bar. |
| mechanical instrument | A conventional instrument that must be manually turned to change face or to locate targets. Compare with servo instrument. |
| MGRS | Military Grid Reference System |
| MSAS | MTSAT Satellite‑Based Augmentation System. A satellite‑based augmentation system (SBAS) that provides a free‑to‑air differential correction service for GNSS over its coverage area, which is Japan. |
| multipath | Interference, similar to ghosting on a television screen. Multipath occurs when GNSS signals traverse different paths before arriving at the antenna. |
| Neighborhood Adjustment | A coordinate adjustment that is applied to conventional surveys with multiple backsights or jobs with a GNSS site calibration. During station setup plus, resection or GNSS site calibration, residuals are calculated for each observed control point. The calculated distances from each new point to the control points used in the station setup or calibration are used to determine the coordinate adjustment to be applied to the new point. |
| NMEA | A standard, established by the National Marine Electronics Association (NMEA), that defines electrical signals, data transmission protocol, timing, and sentence formats for communicating navigation data between marine navigation instruments. |
| NTRIP | Networked Transport of RTCM via Internet Protocol |
| observation | A measurement made at or between points using surveying equipment, including GNSS receivers and conventional instruments. |
| OmniSTAR | A satellite‑based system that broadcasts GPS correction information. |
| P‑code | The `precise' code transmitted by the GPS satellites. Each satellite has a unique code that is modulated onto both the L1 and L2 carrier waves. |
| parity | A form of error checking used in binary digital data storage and transfer. Options for parity checking include Even, Odd, or None. |
| PDOP | Position Dilution of Precision, a unitless figure of merit expressing the relationship between the error in user position and the error in satellite position. |
| PDOP mask | The highest PDOP value at which a receiver will compute positions. |
| point cloud | A collection of data points in 3D space. |
| positioning system | A system of instrumental and computational components for determining geographic position. |
| postprocess | To process satellite data on a computer after it has been collected. |
| postprocessed kinematic survey | A type of GNSS survey. Postprocessed kinematic surveys store raw stop‑and‑go and continuous observations. The data is postprocessed to achieve centimeter‑level precisions. |
| PPM | Parts per million correction that is applied to measured slope distances to correct for the affects of the earth's atmosphere. PPM is determined using observed pressure and temperature readings together with specific instrument constants. |
| precision | A measure of how closely random variables tend to cluster around a computed value, which indicates the repeatability of one or a set of measurements. |
| prism constant | Distance offset between the center of a prism and the point being measured. |
| projection | Used to create flat maps that represent the surface of the earth or parts of that surface. |
| QZSS | Quasi‑Zenith Satellite (QZSS) is a Japanese based satellite system built by the Japan Aerospace Exploration Agency (JAXA). QZSS is a complementary GNSS to the U.S. Global Positioning System (GPS), the Russian GLONASS, and the European Union Galileo positioning system. QZSS is also a satellite‑based augmentation system (SBAS). |
| RDOP | Relative Dilution of Precision. See also DOP . |
| real‑time differential survey | A type of GNSS survey. A real‑time differential survey uses the differential corrections transmitted from a land‑based receiver or from SBAS or OmniSTAR satellites to achieve submeter positioning at the rover. |
| real‑time kinematic and data logging survey | A type of GNSS survey. A real‑time kinematic and data logging survey records raw GNSS data during an RTK survey. The raw data can be postprocessed later, if required. |
| real‑time kinematic and infill survey | A type of GNSS survey. A real‑time kinematic and infill survey allows you to continue a kinematic survey when radio contact with the base station is lost. The infill data must be postprocessed. |
| reference station | See base station. |
| refline | The process of establishing the position of an occupied point relative to a baseline by taking measurements to two known or unknown points. |
| resection | The process of establishing the position of an occupied point by taking measurements to two or more known points. |
| RMS | Root Mean Square. This is used to express the accuracy of point measurement. It is the radius of the error circle within which approximately 70% of position fixes are to be found. |
| RMT | Remote target |
| survey | A survey in which the controller running the Trimble Access software is connected via radio to a conventional instrument, so that the instrument can be controlled robotically from the Trimble Access software. |
| rounds | Conventional observation method of multiple observations to multiple points. |
| rover | Any mobile GNSS receiver and field computer collecting data in the field. The position of a roving receiver can be differentially corrected relative to a stationary base GNSS receiver. |
| RTCM | Radio Technical Commission for Maritime Services. This is a commission that was established to define a differential data link for the real‑time differential correction of roving GNSS receivers. There are two types of RTCM differential correction messages, but all Trimble GNSS receivers use the newer Type 2 or Type 3 RTCM protocol. |
| RTK | Real‑time kinematic, a type of GNSS survey. |
| SBAS | Satellite Based Augmentation System. SBAS is based on differential GNSS, but applies to wide area networks of reference stations (for example, (WAAS, EGNOS, MSAS). Corrections and additional information are broadcast using geostationary satellites. |
| servo instrument |
A conventional instrument that is equipped with servo motors, which enables the instrument to change face and turn to track targets automatically. Compare with a mechanical instrument. If the servo instrument is also equipped with a radio, you can use it in a robotic survey, where the instrument is controlled via the Trimble Access software. |
| single‑frequency | A type of receiver that only uses the L1 GNSS signal. There is no compensation for ionospheric effects. |
| single distance offset | Measurement of horizontal and vertical angles and a slope distance. Plus additional offset distances to position obstructed points. |
| SNR | Signal‑to‑Noise Ratio, a measure of the strength of a satellite signal. SNR ranges from 0 (no signal) to 99, where 99 is perfect and 0 means the satellite is not available. A typical good value is 40. A GNSS system typically starts using a satellite when its SNR value is higher than 25. |
| station | The distance or interval along a line, arc, alignment, road, or tunnel. |
| station setup | The process of defining the instrument occupation point and setting the orientation of the instrument to a backsight point or points. |
| string | A string is a series of 3D points joined together. Each string represents a single feature such as a curb line or the centerline of a road. |
| surface | A surface is a 3D digital representation of topography, formed by a mesh of contiguous triangles, which is stored as a Trimble Terrain Model (TTM) file. |
| superelevation | In terms of a road design, superelevation refers to the addition of an extra slope (banking) on curves of the road to assist vehicles negotiating the curves. Adding superelevation assists in achieving the required design speed for the curve. Superelevation is generally defined in conjunction with widening. |
| SV | Satellite Vehicle (or Space Vehicle). |
| target height | Height of prism above the point being measured. |
| TDOP | Time Dilution of Precision. See also DOP. |
| TOW | Time of Week in seconds, from midnight Saturday night/Sunday morning GPS time. |
| tracking | The process of receiving and recognizing signals from a satellite. |
| Tracklight | A visible light that guides the prism operator on the correct bearing. |
| traverse |
A traverse is formed by surveying a number of points at traverse stations and then linking them into a circuit. A closed traverse is formed when the circuit ends at the starting point. It is useful for surveying large areas which are defined by a boundary. An open traverse is formed when the circuit ends at a different point to the starting point. It is useful for surveying a narrow strip of land such as a coastline or a corridor for a road. A valid traverse station has one or more backsight observations to the previous traverse station, and one or more observations to the next traverse station. To compute a traverse closure, there must be at least one distance measurement between successive points used in the traverse. |
| TRK | Tracking mode. Used to measure towards moving targets. |
| TTM | Trimble Terrain Model file, which represents a 3D terrain surface model as a mesh of contiguous triangles. |
| USNG | United States National Grid |
| UTC | Universal Time Coordinated. A time standard based on local solar mean time at the Greenwich meridian. See also GPS time. |
| VBS | Virtual Base Station |
| VDOP | Vertical Dilution of Precision. See also DOP. |
| vertical circle | Graduated or digital disc from which the vertical angle is measured. |
| VPI | Vertical Point of Intersection |
| WAAS | Wide Area Augmentation System. A satellite‑based augmentation system (SBAS) that improves the accuracy and availability of the basic GNSS signals over its coverage area, which includes the continental United States and outlying parts of Canada and Mexico. |
| Weight exponent | The Weight exponent is used in the Neighborhood adjustment calculation. When the coordinate adjustment to be applied to a new point is calculated, the calculated distances from each new point to the control points used in the station setup are weighted according to the Weight exponent. |
| widening | In terms of a road design this refers to the widening of the road around a curve to provide extra safety for cars negotiating the curve. Widening is generally defined in conjunction with superelevation. |
| WGS‑84 | World Geodetic System (1984), the mathematical ellipsoid used by GPS since January 1987. See also ellipsoid. |
| Y‑code | An encrypted form of the information contained in the Pcode. Satellites transmit Y‑code in place of Pcode when Anti‑Spoofing is in effect. |