The latest geospatial terms can be confusing. We've created the below list of frequently used terms to assist those new to the geospatial world. This list is by no means exhausitive, and includes only the most common terms.
Optical level – https://survey.crkennedy.com.au/construction-lasers-measuring-tools/automatic-levels
A precision optical instrument for measuring points in the same horizontal plane. Also referred to as an automatic level, dumpy level, or level. It is used to measure height differences typically to a staff, and to transfer, measure and set heights.
Theodolite – https://survey.crkennedy.com.au/products/lg789311/prexiso-t-o-2-2--theodolite
A precision optical instrument for measuring angles in both the vertical and horizontal axis.
Total Station – https://survey.crkennedy.com.au/totalstations
A precision electronic optical instrument used for measuring angles in the vertical and horizontal axis, distances with an electronic distance meter (EDM), and an onboard computer for recording data and performing triangulation calculations. Also referred to as a Jigger.
MultiStation – https://survey.crkennedy.com.au/products/lg898871/leica-nova-ms60-1--r2000-multistation
A total station instrument developed by Leica Geosystems that features an integrated (LiDAR) laser scanner capable of capturing a point cloud. An example is the Leica Nova MS60 MultiStation.
Laser Scanner – https://survey.crkennedy.com.au/3dlaserscanning
A laser scanner is a precise instrument that measures vertical and horizontal angles, as well as distances, and stores the points as a point cloud. Typically, it records points at thousands or even millions of points per seconds.
Setout or Stakeout– A setout is a physical process that involves transferring dimensions of positions from plans onto the ground where the construction is to take place. These positions can include features such as Roads, Bridges, building positions, centre lines of walls, boundary lines, plumbing etc. The process can be performed with a total station or GNSS Rover receiver.
Free Station / Resection – A free station setup or resections is the method of determining an unknown Total Station position measuring observations to known coordinated points.
Traverse - Traverse networks involve placing survey stations along a line or path of travel, and then using the previously surveyed points as a base for observing the next point.
Backsight (BS) - A backsight is a Total Station or Level reading taken to a position of known coordinate(s) or height.
Foresight (FS) - A Foresight is a Total Station or Level reading taken to a position of unknown coordinate(s) or height.
Coordinate Transformation / Localisation - Is a process of matching GPS coordinates with the local jobsite coordinates.
Control Network - is the framework of survey stations whose coordinates have been precisely determined and are considered definitive to the project.
Survey Marker/ PSM’s (permanent survey marks) - survey monuments, or geodetic marks, are objects placed to mark key survey points on the Earth's surface. They are used in geodetic and land surveying
GNSS – Global Navigation Satellite System refers to any constellation of navigation satellites systems. This includes constellations such as the USA’s Global Position System (GPS), Russia’s GLONASS, EU’s Galileo, China’s BeiDou, Japan’s QZSS, India’s IRNSS, etc.
Geodetic Datum - A geodetic datum is a reference surface, a coordinate system and a set of defined reference points from which coordinates may be calculated to define a specific location on the Earth’s surface, at a national or global scale. In Australia, geospatial professionals typically use the Geocentric Datum of Australia (GDA) to represent points on a national scale.
Geoid - The geoid is the shape that the ocean surface would take under the influence of the gravity of Earth only. This excludes effects from other factors such as wind, tides, etc. The earth’s gravity is not uniform across its surface, so the geoids representation is not smooth but lumpy.
Ellipsoid – An ellipsoid is the closed surface of a deformed sphere. The Earth is not perfectly spherical as it bulges at the equator. An ellipsoid is a mathematical representation of the Earth’s surface. However, the Earth’s shape is not a perfect ellipsoid as it has deep ocean trenches, high mountain ranges, irregular sea levels, etc.
Geocentric Datum of Australia (GDA) - The Geocentric Datum of Australia 2020 (GDA2020) is the current Australian datum for coordinates. It is a static datum and is closely aligned to GNSS global reference frames.
Real-time kinematic (RTK) GNSS - RTK technology provides real-time GNSS correction, it is an accurate technique used to determine the position of a GNSS receiver using signals received from satellite-based positioning systems.
Post Process Kinematic (PPK) GNSS - The PPK survey requires simultaneous collection of static data from a CORS or static base and a moving GPS rover to locate the measured points, the methodology demands specialized software for post processing. .
GNSS Base Station - A Base-Station is a station where a GNSS receiver is installed at a known location also called a Reference station. An RTK GNSS base station transmits an RTK correction via the internet or UHF.
Continuously Operating Reference Stations (CORS) Network - https://survey.crkennedy.com.au/hxgn-smartnet
Is a network of GNSS base stations that log static data and broadcast RTK corrections, usually over an Internet connection. With more than 4,000 reference stations, Hxgn SmartNet is Australia’s largest CORS network, and provides both RTK and PPK corrections to GNSS users.
GNSS Rover - https://survey.crkennedy.com.au/gps-gnss
An RTK rover uses GNSS signals plus RTK corrections from the GNSS base station to calculate a coordinate position to measure and set out survey points. The Leica GS18 RTK rover is a GNSS rover.
Point Cloud – A point cloud is a set of data points in the same coordinate system. Each point will have cartesian coordinates (X,Y,Z) as a minimum. Additional values can include colour (red, green, blue), intensity, surface normal, waveform properties, etc. Point clouds can be visually represented with colours on heights, reflectivity, colour, or other properties. Typically point clouds are acquired using a laser scanner, although they can also be generated through photogrammetry.
LiDAR - Lidar is an acronym of "light detection and ranging" or "laser imaging, detection, and ranging". Lidar is a method for determining ranges by targeting an object or a surface with a laser and measuring the time for the reflected light to return to the receiver.
Digital Twin – This term refers to a digitised copy of a physical asset.
Computer-aided Design (CAD) – A CAD model is simple a 3D virtual computer model. Note, it is not a point cloud, but CAD models can be designed from point clouds.
Building Information Modellings (BIM) – BIM refers to a process of creating and managing information for a built asset. This includes the initial design phase, construction phase, operation phase, and end-of-life decommissioning. Note, CAD software packages or CAD models are not BIM, but enable part of the BIM process.
Feature Codes: Surveying feature codes are typically abbreviations of 2-4 letters used by surveyors to label points of interest measured in the field. For example, rather than typing out “permanent survey marker”, a surveyor will enter the code “PM”. There is no universal agreement on feature codes, so these will be different depending on the surveying company or government organisation.
Digital Terrain Model (DTM): Also known as a Digital Elevation Model (DEM), DTMs are a 3D computer representation of terrain. It’s often represented as a raster (a grid of squares, also known as a heightmap when representing elevation) or as a vector-based triangular irregular network (TIN) mesh.
GIS
Geographic Information System (GIS) is a database or computer system of location data combined with tools for managing, visualising, and analysing the data. It’s a separate discipline from surveying, and typically does not require the same level of accuracy. GIS typically displays multiple data sets on one map, allowing users to easily visualise the data. For example, a local government might have a GIS database with data layers displaying vegetation, animal habitats, buildings, road infrastructure, underground pipes, etc, overlayed on one digital map.
Photogrammetry
Photogrammetry uses two-dimensional imagery to extract spatial data. Three-dimensional data can be extracted from two dimensional photographs by measuring the distance between two points that lie on a plane parallel to the photographic image plane. In surveying images can be collected from drones or cameras mounted in surveying equipment and post processed using photogrammetry to create points clouds or calculate the position of single points using multiple images. Leading photogrammetry software includes Pix4D, Leica Infinity and DJI Terra.
Orthomosaic
An orthomosaic is a photogrammetrically orthorectified mosaic image. Multiple photos have been stitched together to create one single mosaic image. The geometric distortion has been rectified and the colour has been balanced to produce a seamless orthographic mosaic dataset.
Ground Control Point (GCP)
A ground control point (GCP) is a point is a maker with a known coordinate. Typically, a GCP’s coordinate can be measured with an RTK GNSS rover. GCP’s are often used when acquiring imagery with a drone for photogrammetry. The known coordinate of the GCP improves accuracy of the data set, and also allows the data set’s coordinate system to be transformed to a different coordinate system (e.g. transforming from WGS84 to the Geodetic Datum of Australia).
