Glossary of Surveying Terms

Total Station

A total station is the workhorse of the modern land or engineering surveyor’s arsenal. It combines several functions that historically would have been fulfilled by a number of different pieces of equipment. A total station combines an electronic theodolite, and electronic distance measurer, and a microprocessor. It can therefore measure horizontal and vertical angles, measure the distance between the instrument and a target, compute the coordinates od a point, and store all of this data ready to be transferred to a computer for processing.

Total stations can also contain a GNSS connectivity function, and a 3D laser scanner function.
The total station is used across geospatial survey disciplines and can be employed to carry out topographical surveys, measured building surveys, and as-built surveys. They are also employed in deformation (monitoring) surveys, volumetric surveys, and a variety of tasks associated with engineering surveys such as setting out.

Terrestrial Laser Scanner

A terrestrial scanner is a relatively new although now indispensable piece of equipment that came into mainstream use in the early 2000s. A scanner can fulfil a number of roles using LiDAR (Light Detection and Ranging), emitting millions of pulses of laser light and combining the subsequent data on distance and angle to capture highly accurate spatial data on its surroundings. The result is a point cloud – a three-dimensional representation of the surveyed area. The point cloud can then be used to create a number of deliverables including AutoCAD drawings and 3D models in a number of formats, including Revit which can then go on to form the basis of a BIM (Building information Modelling) model. Scanners can be stationary, or person/vehicle mounted to capture continuous data whilst in motion. They are particularly useful for capturing data on complex buildings due to their high levels of accuracy, rapid data collection, and rich data output.

Simultaneous Location and Mapping (SLAM)

Simultaneous location and mapping allows a device to map an environment and simultaneously determine its location within it without the use of GNSS/GPS. As it moves through an environment, the device detects common features between scans. Matching these features allows the device to estimate the device’s current position, and the geometry of the environment. It is able to do so using a combination of LiDAR sensors, cameras, and inertial measurement units

Inertial Measurement Unit (IMU)

An electronic sensor that uses a combination of accelerometers and gyroscopes to measure a body’s linear acceleration and angular velocity. These devices track a body’s motion in three-dimensional space

Light Detection and Ranging (LiDAR)

LiDAR refers a remote sensing technology that uses laser pulses to measure the distance between the device in question and a given surface. This is achieved by measuring the amount of time it takes for the laser to travel to the surface and reflect back to the sensor. When employed in a modern laser scanner that emits millions of laser pulses during a scan LiDAR builds a highly accurate 3D point cloud – a digital model of the subject area. LiDAR sensors can be terrestrial (stationary), mobile (mounted on a moving vehicle or person), aerial (mounted on a drone or other aircraft), or bathymetric (designed to penetrate water to map riverbeds or the like).

GNSS Equipment

GNSS is a general term for any satellite-based system that provides global positioning, navigation, and timing services. In the west this is usually the USA’s GPS system, but it can also include other systems such as Europe’s Galileo or Russia’s GLASNASS systems. Leica equipment does not use a single satellite constellation and is compatible with all major global navigation satellite systems.

Unmanned Aerial System (UAS)

An unmanned aerial system refers to the complete setup required to operate an unmanned aircraft – not just the flying element. This is important as it refers to additional elements which contribute to the safe and effective operation of the aircraft or UAV (unmanned aerial vehicle).

The UAS can include:

• UAV
• Ground control station – handheld controller or another device, such as a laptop, used by the operator to control the UAV
• Communication links
• Payloads
• Supporting equipment – landing pad, GNSS base station, batteries, charger, etc.
• Personnel – pilot and spotter

Matterport Camera

A Matterport camera is a 3D imaging device usually used to capture photo-realistic digital models of real-world environments. They are most commonly used to create 3D virtual tours. There are several different types of Matterport camera with varying degrees of accuracy and functionality. They use a combination of high-resolution photography, infrared depth sensing, LiDAR, and AI -driven spatial reconstruction to render a 3D environment that is then hosted online, allowing a viewer to move through the space and take measurements.

CAT and Genny

This refers to a cable avoidance tool (CAT) and signal generator (genny) – a paired system used to locate underground cables and metallic pipes prior to excavation or other intrusive works. This is a key piece of equipment utilised by our utilities surveyors during PAS-128 compliant underground services surveys. The CAT is a handheld device that detects the electromagnetic fields generated by metallic services. The genny is a transmitter that is attached to an accessible part of a buried metallic service that induces a radio signal onto the line that the CAT can then detect. Surveyors can then trace and mark the route of said services below the ground. The CAT and genny is limited in that it can only help to detect metallic services, not plastic or other non-conductive materials that don’t have tracer wires attached. The CAT and genny are primarily used in Detection Category Type B surveys – “Detection by ground penetrating radar and/or electromagnetic locating techniques”.

Topographical Survey

Alternatively known as a land survey or topographic survey, a topographical survey is a precise and detailed mapping of the natural and man-made features on a piece of land. Various pieces of equipment can be used to capture the detail required for a topographical survey, including:

• Total station and detailing pole
• Drone with photogrammetry or LiDAR payload
• Terrestrial or mobile scanner
• GNSS device

The survey captures the contours and elevation of the ground surface, as well as other permanent features within the subject area, such as:

• Buildings
• Boundaries and fences
• Vegetation
• Watercourses
• Roads and footpaths
• Utility covers and visible service routes

A topographical survey might be needed for a number of applications and usually forms a reliable base plan for construction project stakeholders such as architects, planners, engineers, and builders. A topographical survey can be used to:

Underground Services Survey

Also known as a utility survey or PAS 128 survey, an underground services survey involves the location, identification, and mapping of buried utilities and services in a designated area. The main application of a utility survey is to avoid a utility strike – inadvertent damage of a buried service such as gas, water, electric, or telecoms during future excavation. A utility strike can prove incredibly costly to a project in both time and monetary terms.

Typically, underground services surveys involve several non-invasive processes and detection technologies, including:

• Site records and utility plans (statutory searches) sourced from utility providers and other existing sources
• Electromagnetic location (EML) equipment (CAT & Genny)
• Ground Penetrating Radar (GPR)
• Topographical referencing to georeference the detected utilities

Results are presented in AutoCAD format or a 3D model showing depth and direction of services. Services we can detect in our utilities surveys include:

• Computer cables
• Drainage manholes, depths to invert, pipe sizes, direction of flow
• Pipe routes connected to sewers and drains of 100mm and above, where access to the pipe work is possible
• Underground heating pipes
• Water pipes of 38mm and above
• Gas pipes of 38mm and above
• Fuel pipes of 38mm and above
• Pumping mains of 38mm and above
• Telecom and data services in ducts
• Electric supply cables of 440v to 132kv, which are live
• Electric cables to street lighting
• Voids, features and anomalies (where detectable)

In addition to avoiding utility strikes during excavation,n other reasons an underground services survey may be required include:

• Asset management
• Aiding design
• Assessing drainage capacity (especially when in conjunction with a CCTV drainage survey)

Measured Building Survey

A measured building survey comprises the capture of a structure’s physical dimensions and their highly accurate representation in a format of the client’s choosing. Dimensions can be captured using more traditional techniques, such as on paper using a tape measure, laser distometer, and total station, but are now typically carried out using LiDAR-based 3D scanners, either terrestrial, mobile or UAV-mounted. Outputs usually comprise floor plans, elevations, and sections in AutoCAD or similar and/or 3D models in various formats such as Revit, which can then feed into Building Information Modelling (BIM) workflows.

Measured building surveys can provide the basis for many different design and construction projects and are often a requirement of architects, asset managers, and developers. Plans can also be delivered to correspond with Land Registry requirements, illustrate lease plans, and with area calculations based on the client’s choice of methodology, such as International Property Measurement Standards (IPMS).

Pas 128

PAS 128 refers to a standard set out by the British Standards Institution – the latest version being PAS 128:2022 Specification for Underground Utility Detection, Verification and Location. This standard provides guidance on how to accurately map underground utility networks and is useful for both practitioners and clients. It covers:

• Project planning and the scoping process
• A classification system for quality levels based on survey type, location accuracy, inclusion of post-processing, and level of supporting data
• Desktop utility records search
• Detection
• Verification
• Location
• Deliverables

PAS 128 defines four recognised survey types:

PAS 128 also defines Quality Levels (QLs) to describe confidence in positional accuracy:

Ground Penetrating Radar (GPR)

Ground Penetrating Radar is a non-intrusive geophysical surveying technique used to detect and aid in the mapping of subsurface features. GPR devices use high-frequency electromagnetic (radio) waves emitted from a transmitter and picked up by a receiver. The emitter pulses the radio waves into the ground, and the receiver records the signals that bounce back after they hit buried objects or layers below the ground with different electrical properties. By measuring the timing and strength of these reflections, the onboard computer can create a detailed cross-sectional image, or radagram of the subsurface

GPR can be used to locate:

• Sub-surface structures. Anything from foundations to archaeological remains (think Time Team)
• Detecting subsurface voids – anything from badger sets to culverts
• Underground utilities (pipes, cables, ducts) for mapping or maintenance purposes
• Reinforcement in concrete (rebar, post-tension cables)
• Changes in sub-surface composition, i.e. changes in soil type or groundwater level

GPR is not limited to use on the ground. It can also be employed to detect services, voids, or rebars in walls.

GPR is an essential tool in the utility surveyors’ arsenal as it provides an accurate, non-intrusive snapshot of what may lie beneath the ground. It is capable of providing high-resolution data across large areas, especially with larger arrays that can be vehicle- or even UAV-mounted. It is also essential when carrying out a survey to PAS 128 standards.

Sonde

A sonde is a battery-powered radio transmitter used to trace the route and depth of non-metallic underground services. This can include such as plastic drainage pipes, ducting, sewers, and culverts. A sonde comes into play when services cannot be detected by standard electromagnetic locators. It can also be referred to as a beacon, probe, or traceable transmitter.