Glossary of Terms

AccuGrade

Brand name for Caterpillar's machine control system. In 2002 Caterpillar and Trimble formed a 50/50 joint venture (called Caterpillar Trimble Control Technologies) which was responsible for developing both Cat's AccuGrade and Trimble's GCS900 machine guidance systems. As such, most of the components are interchangeable between these two systems. AccuGrade can be installed on a variety of machine types including graders, excavators, dozers, scrapers, compactors and more. The AccuGrade system can take advantage of numerous positioning techniques including GPS, laser and total station.

Almanac

A set of data about the satellite constellation used to assist GPS receivers in the translation of satellite signals. Almanac information is transmitted with the satellite position signal and includes data such as current satellite health, course of orbit and atomic clock calibration. When a receiver has been moved significant distances or hard reset, it may take up to 15 minutes to download the almanac information and determine a fixed GPS position.

ATS (Advanced Tracking System)

Trimble robotic total station that can be used for positioning both survey devices and machine control systems. ATS has been replaced with UTS (Universal Total Station) to perform better with Trimble's GCS900 3D machine systems. However the term ATS is often still used in the construction industry to describe a Trimble total-station guided grader.

Autonomous

Self-functioning, stand-alone, independent. Autonomous GPS works purely off satellite information without any reference source (base station). Once the satellite solution has been fixed, autonomous GPS provides accuracies of approximately 15 metres. This amount of error is OK for basic systems such as your car or boat navigators but is not usually adequate for machine guided construction.

Avoidance Zone

Areas that for a variety of reasons have been identified as no-go zones that cannot be entered. Avoidance zones can be integrated into some machine control systems effectively creating a virtual fence. Avoidance zones can be viewed on the machine control display and breaches of the zones can be reported both to the machine operator and to external parties via wireless communication methods (including SMS text messaging).

Base station

A satellite receiver that is established over a known location and transmits corrections to the roving receivers (including GPS machine control systems). Base stations are an essential component to Differential GPS (DGPS) and Real Time Kinematic (RTK) positioning methods.

Batter board

A traditional survey setout tool. Two stakes are placed in-line on chainage. A board (or 3rd stake) is then nailed between them on the slope of the design batter. Cut batter boards are placed so the top of the board is at finished design level - a grade checker is then able to string between the boards and sight down the boards / stringline to determine whether the batter is following design slope. A fill batter board is generally built so that the top of the board is 1 meter above finished design level and the grade checker can use a 1m high rod (or similar) to sight through to the fill batter board. Machine guided construction eliminates the need for traditional survey batter boards and grade checkers.

Benchmark

A marked point of know elevation from which other elevations may be established. Surveyors may establish a benchmark for machine control plant to use as an accuracy check. Total station graders in particular may use a benchmark (sometimes called a Grader Benchmark - GBM) to fine turn and/or confirm their accuracy before final pavement trimming.

CAD (Computer Aided Design)

A computer software program used for design, drafting and/or presentation of graphics such as construction drawings. There are many different CAD software packages focusing on the needs of different users. Most machine control systems offer basic CAD software in-built into their display for the creation of simple designs in the field. More complex design models are created on office-based CAD software programs.

Chainage

The running distance along a curved or straight line from a fixed commencing point. Deriving from the word chain which was a length historically measured by a surveyor's chain (tape). A chain is 20.1168 metres with 10 square chains making an acre. The chain is no longer used for practical survey work. However the term chainage (sometimes called station) is often used together with an alignment offset as a location identifier.

Control Box

The cab-mounted display of a machine control system. The control box is the brains of the machine control system. It takes all of the inputs provided by the machine control hardware components and processes them instantly to display real-time guidance to the operator. All system options are configured through the control box.

Control Station

A marked point of known position both horizontally and vertically. Control station networks are established on most construction and mining sites and are used as fixed references for positioning other surveyed features. Control stations are essential for machine guided construction and surveying in general. GPS base stations are set up over a control station. GPS rover results are checked on control stations. Lasers are generally set up over a control station for elevation determination. Total stations require control stations in order for an instrument position to be fixed.

Coordinates

A set of numbers that is used to determine a relative position. Machine control designs usually refer to an Easting and Northing for horizontal position and Elevation or Reduced Level (RL) for vertical position.

Cross-section view

A view that represents a section cut perpendicularly along a plane through the intended design surface. A machine control cross-section displays the machine and/or ground engaging tools superimposed over the design model, graphically representing where the machine is currently located versus where the design is intended to be.

Design

A paper-based representation of the intended final construction product. Although usually created from a computer-based CAD package, the design is usually used to provide design guidance at certain critical areas, whereas a model contains all of the detailed design information. A paper-based design is usually used as the basis of a digital design model.

Diagnostics

A machine control system trouble-shooting tool. There are many complex components to a machine control system and many different possibilities of system errors. A diagnostic tool provides assistance for identifying potential system faults and/or faulty hardware components. Some machine control systems offer remote diagnostics that allow a support professional to access trouble-shooting information remotely via a cell modem or similar, reducing downtime and costs.

Differential GPS (DGPS)

A technique for adjusting the inherent inaccuracies of satellite signal transmissions and atmospheric interference. An independent base receiver is established over a known mark. By receiving the same information as the roving receiver, the base is able to transmit satellite signal corrections (the "differential") to the rover. DGPS typical achieves an accuracy of 1-2 metres making it more accurate than Autonomous GPS but less accurate than RTK GPS.

Dilution of Precision (DOP)

A measurement of the errors in satellite signal geometry, usually from the satellites being clustered too close together in one quadrant of the sky. Position Dilution of Precision (PDOP) is the most commonly quoted DOP value although DOP can also be measured in Geometric (GDOP), Vertical (VDOP), Horizontal (HDOP) and Time (TDOP). A lower value DOP represents better geometry.

DTM (Digital Terrain Model)

The most commonly utilised computer-based modelling technique that uses a series of connected triangles to create a complete digital representation of the intended surface. DTM's are often used as the basis of machine control design model surfaces.

Dual Antenna

Some machine control systems / applications use two satellite antennas mounted on the machine. With a GPS satellite antenna mounted on both sides of the machine, orientation is almost immediate and the functionality of the machine can be maximised. For example, a single antenna grader may not be able to lean the front wheels over if there is no sensor in use that can measure this movement, however a grader with satellite antennas mounted on either side of the blade can. Note that a single antenna grader is able to use a combination of an instrument and machine target to acquire positioning while a dual antenna cannot - the total station can only read one target and without sensors the position of the non-antenna side of the machine would be unknown.

Easting

The east / west horizontal value of a coordinate positioning grid. Combined together, easting and northing determines a relative horizontal position.

Elevation

The height component of coordinate positioning grid. Elevation is the distance in metres above an assumed and mathematically-smoothed mean sea level.

Fix

The determination of a GPS receiver's location. Most receivers compute this position fix once every second.

Float

The state of an RTK satellite receiver before it has achieved a fix.

GCS900

Machine grade control system by Trimble. Rather than differentiating, the GCS900 brand name covers almost all machine types and system configurations. GCS900 can be installed on graders, excavators, dozers, scrapers, compactors, etc with equipment able to be easily hot-swapped between different plant types. Slight variations of the brand exist for roller / compactors (CCS900) and pavers (PCS900). The system comes in 2D and 3D configurations and can be guided by a variety of methods including GPS, laser and total station.

GLONASS (Global Navigation Satellite System)

The Russian satellite constellation. GLONASS was developed by the former Soviet Union (USSR). After falling into disrepair after the fall of the USSR, GLONASS was restored by the Russian government to a full orbital constellation of 24 satellites in 2010 providing full global coverage. It now provides both a compliment and a complete alternative to the American GPS satellite system.

GNSS (Global Navigation Satellite System)

A system of satellites and control stations that provides geo-spatial positioning with global coverage. Technically speaking, the American GPS system is a GNSS as is the Russian GLONASS system. GNSS usually refers to the use of a combination of both systems. China's Compass satellite system and the European Union's Galileo system are being developed as new GNSS systems but have not yet achieved full global coverage. When operational, all four systems are expected to be available free of charge both independently and as part of the future GNSS collective network.

GPS (Global Positioning System)

The American satellite constellation. The GPS network was the first fully operational satellite navigation system. It was created and is maintained by the United States Department of Defence. Initially developed as a military tool, the satellite codes have been released to the general public, making GPS positioning data freely accessible to anyone with a GPS receiver. While technically speaking GPS refers to the American satellite constellation, the term GPS is widely used to describe the combined GNSS satellite network.

GPS+

The brand name for Topcon's base model machine control system using GPS and GLONASS satellite signals. GPS+ can be installed on graders, dozers and scrapers and can also be easily upgraded to turn into an LPS-900 (total station guided) or Millimeter GPS (laser augmented) machine control system.

Horizontal offset

A movement of the horizontal design data. It is often desirable to obtain guidance to a design feature at a specified horizontal offset. Machine control systems allow an operator to mirror a design feature at a selected horizontal distance. For example, a grader may wish to over-build a formation to 200mm wider than the intended design. This can be achieved by horizontally offsetting the road edge feature and following the new guidance line.

Initialisation

An initial value. In RTK this term describes the process of obtaining the first position fix. RTK can take up to 1 minute to achieve initialisation.

Laser augmentation

A machine control positioning technique that combines GPS satellite horizontal position with laser-guided elevations, thus improving final grading. Satellite horizontal positioning is generally accurate to +/- 25mm while laser guided levels bring vertical accuracies down to approx +/- 10-15mm.

Latency

Delay. In GPS terms, this refers to the lag period between receiving the satellite information (including base receiver corrections in DGPS or RTK) and the solution being generated by the roving receiver. When moving a lower latency is desirable to reduce positional errors for a GPS in motion. This is particularly relevant in machine control applications and manufacturers are continuously developing new methods and technologies to reduce latency.

Latitude / Longitude

A location expressed by angular distances. Latitude is measured north or south of the earth's equator. Longitude is measured east or west of the Greenwich meridian. The terms are often abbreviated to Lat / Long. Most construction and mining sites use localised grid-based coordinates (Easting and Northing) rather than Latitude and Longitude.

Leica

Leica Geosystems is one of the 3 major manufacturers of machine control products. A brand best known for its high quality cameras, Leica's roots are heavily based in the surveying industry. Leica Geosystems was formed in 1990 after a merger of several companies including pioneering survey optics company Wild. Leica Geosystems is based in Switzerland.

Lightbar

A device that uses lights to graphically display cut/fill information to a machine control operator. Lightbars are generally mounted inside the machine cab in such a way as to allow the operator easy reference to basic position data without taking their eyes off the machine's ground-engaging tools.

LPS-900

The brand name for Topcon's total station machine control system. This system does share components with other Topcon machine control products, making it possible to be reconfigured. LPS-900 can be installed on graders and dozers.

Machine automation

A form of machine control technology that not only displays the machine's position over a design model but also directly controls the machine's ground engaging tools. By controlling the machine hydraulics, the system is able to automatically move the blade / bucket towards the correct grade allowing the operator to concentrate on driving the machine. Construction accuracies can be greatly improved by using automated machine control systems.

Machine control

The generic term used to define the integration of survey positioning devices with construction plant.

Machine guidance

A form of machine control technology that is indicate-only. The system is able to guide the operator to the correct position and grade by showing the current machine position against the desired design. Unlike machine automation, the system does not have the ability to directly control the machine's ground engaging tools.

Machine guided construction

The concept of using machine control systems as a construction methodology, effectively eliminating the need for traditional survey stakes. More and more construction companies are realising the numerous benefits of utilising machine control systems to create peg-less sites.

Millimeter GPS

The brand name for Topcon's most popular final trim machine control positioning solution. Millimeter GPS is a laser augmented system that combines satellite-based horizontal position with the more accurate laser based vertical position. Millimeter GPS can be installed on graders and dozers.

Model

A computer-generated, three-dimensional surface that is produced to represent the intended construction design. All 3D machine control systems use design models for design reference. These models must be compiled and checked for consistency using design software packages.

Multipath

Satellite signal refraction (bending). Multipath can be a major source of GPS inaccuracy. It can occur when the satellite signal travels through the earth's atmosphere and can also occur when close to certain metal objects such as chain wire fences.

NAVSTAR

NAvigation Satellite Timing And Ranging. The official name of the United States of America's GPS System.

Northing

The north / south horizontal value of a coordinate positioning grid. Combined together, easting and northing determines a relative horizontal position.

Offset

Away from the control line. Offset is a horizontal positioning term often used in conjunction with chainage to describe a location on a jobsite. When looking down chainage, a negative offset refers to a position left of the control line and a positive offset is to the right of the control line.

PDOP (Position Dilution of Precision)

A commonly used measurement of the accuracy of the satellite signal geometry. The accuracy of satellite geometry changes as the constellations move across the sky and studying the PDOP allows a user to determine when the best GPS accuracy can be achieved. A lower PDOP value is better. When the PDOP value is above 6 the user should be cautious of significant errors in satellite guidance. A PDOP value above 10 would indicate unacceptable errors in machine guided construction.

Peg

Wooden stake used for survey setout. Officially a peg is a relatively short boundary setout tool. In Australian construction terminology there is little difference between the terms peg and stake. Survey pegs are driven into the ground using sledgehammers in traditional construction survey techniques and used to mark various design features such as batter hinge points, drainage lines and pavement edges. Design levels are usually marked on the pegs. String lines are often strung between sets of pegs allowing grade checkers to dip a tape measure to determine as-constructed levels.

Pegless site

The concept of being able to perform civil construction projects without the need for traditional survey pegs / stakes. Replacing traditional survey staking with plant-mounted machine guidance systems results in significant cost benefits due to less survey field requirements and the elimination of earthworks grade checkers / string liners.

Plan view

A graphical representation of the intended design taken by looking down upon it. A machine control plan view displays the machine and/or ground engaging tools superimposed over the lines of the design model. Machine operators can then view design features (e.g. road widenings) and their locations in relation to the machine's current position.

Power module

The specific machine control mechanism that regulates power delivery to the various other system components. Errors in system performance can often be traced back to the power module.

PowerDigger

The brand name for Leica Geosystem's 3D machine control system for excavators. The system is a dual antenna configuration that can be guided by both GPS and total station positioning techniques. PowerDigger shares similar product components with Leica's PowerGrade.

PowerGrade

The brand name for Leica Geosystem's 3D machine control system for graders, dozers and scrapers. The system is a single antenna configuration that includes sensors to assist the determination of the blade tips. PowerGrade can be guided by GPS, laser receiver and total station positioning techniques.

Profile view

A view that represents a section cut parallel along the length of an intended design. A machine control profile view displays the machine and/or ground engaging tools along with the profile of the design. The operator is then able to determine any longitudinal changes of grade in the design model.

Receiver

The hardware component that reads and interprets satellite information allowing for the transformation into Earth-based position data.

RL (Reduced Level)

The vertical distance between a survey point and the adopted level datum (reference level). Often a more localised datum reference is assumed but if the datum reference used is mean sea level, RL will be the same as Elevation.

Rover

Roving (moving) GPS satellite receiver including those used by surveyors and those used by machine control - although a surveyor's receiver is most commonly referred to as a 'rover'. In DGPS or RTK these are used to determine accurate positions with assistance from corrections transmitted from the GPS base station.

RTK (Real Time Kinematic)

A specialised GPS survey technique that provides vertical accuracies of +/- 30mm. Kinematic is derived from a Greek word that means "to move" and RTK allows more accurate GPS measurements whilst moving around. Like Differential GPS (DGPS), RTK uses a base station to transmit satellite corrections to the roving receiver. RTK uses different satellite signal wavelength measurements and complex mathematical equations to increase its accuracy. As a result, RTK solutions are the most expensive technology and acquiring a lock takes slightly longer than DGPS (less than 1 minute versus instant lock). However because of its accuracy, RTK has become the method of choice for most civil construction survey and machine control operations.

Satellite

A device designed to be launched into orbit around the Earth. GPS satellites broadcast position signals back to Earth than can be used for positioning techniques including machine control systems.

Sensor

Machine control mechanism that is used to measure the movement of a specific component of a machine. For example, a grader-mounted blade sensor is responsible for measuring the current angle of a grader blade. Example grader components that may require sensor measurements include blade slope, blade pitch, machine pitch and circle rotation. Excavators may have sensors that measure angles on the machine pitch, boom, stick and bucket. All sensor readouts are combined with any other positional information (e.g. GPS or total station guidance) to determine the exact position of the ground-engaging tools.

Single antenna

Some machine control systems / applications use a single satellite antenna mounted on the machine. This is then coupled with one or a variety of sensors to determine the tips of the ground breaking attachments. Single antenna systems can be cheaper than dual antenna systems but can limit the functionality of both the machine control system and the machine. For example, a single antenna grader may not be able to lean the front wheels over if there is no sensor in use that can measure this distance, however a grader with satellite antennas mounted on either side of the blade can. Note that a single antenna grader is able to use a combination of an instrument and machine target to acquire positioning while a dual antenna cannot.

Smart antenna

Smart antennas contain a GPS antenna and receiver in the one unit. Rather than having the two components mounted in separate areas of the machine, the smart antenna computes the satellite signal directly upon receiving it. This makes the smart antenna more portable and easier to convert the machine guidance system between the various positioning techniques (GPS, laser striker or total station). A smart antenna is also easier to transfer between machines.

Stake

Wood peg of various sizes with spiked ends used in survey setout. Survey stakes are driven into the ground using sledgehammers in traditional construction survey techniques. Stakes mark various design features such as batter hinge points, drainage lines and pavement edges. Design levels are usually marked on the stakes. String lines are often strung between sets of stakes allowing grade checkers to dip a tape measure to determine as-constructed levels.

Supervisor Kit

Car-mounted GPS reference systems designed for use by supervisors and client inspectors. With the invent of a peg-less site due to machine control access to design information, supervisors were left with little design information to reference. The solution to this was to mount relatively inexpensive GPS devices directly to the supervisor's on-site vehicles. With windscreen-mounted displays, supervisor kits present real-time position and design information directly to the supervisor and constantly updates as they are driving throughout their work areas.

Surveying

The accurate determination of the absolute and relative positions of three dimensional points and the angles and distances between them. Surveying involves the science and art of making all essential measurements to determine the relative position of points on the Earth's surface. Construction and mining surveyors are (amongst other things) responsible for converting the intended design into a useable model, positioning the design on the ground for construction use and checking the as-constructed results against the design to confirm conformance.

Topcon

Topcon Positioning System is one of the 3 major manufacturers of machine control products. For many years Topcon was the only product machine control products that could track the GLONASS Russian satellite constellation (now offered by all major manufacturers). Topcon is a Japanese based company although its satellite positioning software is primarily developed in Russia.

Total Station

An electronic survey instrument that combines a theodolite and distance meter. Machine-mounted targets can be robotically measured by total stations to provide very accurate positioning data in real time. Machine control accuracies of +/- 5mm can be achieved using total station positioning, meaning these systems are usually reserved for final pavement operations.

Triangulation

The mathematical process of determining an accurate position based on forming triangles with at least two known points. Distances and angles are measured and a position determined with the help of trigonometry. A total station is usually positioned by performing a resection of at least 2 known points (preferably 3 for redundancy) and using triangulation to determine the instruments position.

Trilateration

The mathematical process of determining an absolute or relative position by measuring its distance from other objects. Trilateration does not use angle measurements in its position determination. GPS receivers measure the distance (calculated by multiplying the speed of light by the delay in transmit time) to at least 4 satellites and uses trilateration to determine its known position within an expected error.

Trimble

Trimble Navigation is one of the 3 major manufacturers of machine control products. Trimble machine control products have benefited from technologies acquired through the company's many mergers and acquisitions. Trimble also benefits from a joint venture with plant manufacturer Caterpillar. The two companies have created a joint distribution channel called SITECH who sell and support both Trimble-branded GCS900 and Caterpillar-branded Accugrade products. Trimble is an American company headquartered in Sunnyvale, California.

UTS (Universal Total Station)

Trimble robotic total station that can be used for positioning both survey devices and machine control systems. UTS replaced the older ATS (Advanced Tracking Sensor) total station instruments.

Valve module

The specific mechanism that is used to control the movement of a machine's lift cylinders when equipped with machine control automation. When in automatic mode, the machine control system takes control of the machine valves allowing the ground-engaging tools to maintain a desired grade, increasing machine productivity and accuracy.

Vertical offset

A movement of the design surface either up or down. This is one of the most commonly used functions of a machine control system. The system will allow an operator to raise or lower a design surface for a specific operation. The design model loaded into a machine control system may be set to display the finished level surface. If, for example, a grader wishes to build a subgrade surface at 500mm below F.L. the system will allow them to lower the design model to accommodate this. Revised cut/fill information will then be displayed to the operator guiding them to the lower surface.

VRS (Virtual Reference Station)

A Trimble-developed advanced RTK (Real Time Kinematic) GPS solution that uses multiple reference base stations in unison and a central processing server to provide accurate satellite corrections.

Wireless connection

The concept of acquiring a two-way data flow between the machine control plant and office-based software via cellular modem, radio or similar. Remotely accessing machine control systems from a centralised location provides numerous construction benefits such as being able to send and remove design files, perform remote troubleshooting diagnostics and acquiring position data logged by the machine.

X63

The brand name for Topcon's 3D machine control system for excavators. The system uses a dual satellite antenna configuration. The X63 is a satellite-based system only and cannot be guided by total station positioning techniques.

2D

Two dimensional. For machine control, 2D refers to the ability to acquire indicative guidance relative to a predetermined target. 2D machine systems are programmed with all the machine dimensions so the system knows where the cutting tips are in relation to one another. 2D machine control systems do not utilise GPS receivers or other remote positioning devices. As such, 2D machine control is considered the basic machine guidance system and will not reference a machine in relation to the jobsite, but it definitely does still have its uses. An example of the use of a 2D machine control system would be a grader that is following an existing road kerb at a consistent cross grade - the as-built kerb becomes the reference target.

3D

Three dimensional. 3D machine control is a more comprehensive system than 2D systems. 3D machine control systems use the same machine dimension and setup information as 2D but also include the ability to be positioned on the Earth via positioning techniques such as GPS, total station or similar. As the machine moves around its exact location in relation to the jobsite is displayed. Comparisons against a design model will result in accurate and real-time cut/fill information on a 3D machine control system.

3Di

The brand name for Topcon's base model machine control system for graders, dozers and scrapers. 3Di is an indicate-only system meaning it does not provide automatic blade control. 3Di is a satellite-based system and cannot be guided by laser or total station. Topcon 3Di can be upgraded to GPS+, LPS-900 or Millimeter GPS by adding additional components and software options.

3D-MC²

Pronounced '3D MC squared' this is the brand name of Topcon's GPS machine control system for dozers and graders that incorporates an inertia sensor. In theory, an inertia sensor allows the machine control system to better predict the movement of the machine and thus make faster blade tip allowances, translating to 3D guidance at faster machine speeds. 3D-MC² is a satellite guided system but can be re-configured for other positioning techniques.