PEC EPE Geoinformatics key terms

A defined set of parameters, including an ellipsoid and its position and orientation relative to the Earth, that fixes the origin and axes for a coordinate system so positions can be expressed numerically.

The equipotential surface of the Earth's gravity field that coincides with mean sea level, extended under the continents; it is the physical reference surface for orthometric heights.

The height of a point above the reference ellipsoid, measured along the ellipsoid normal. GNSS receivers determine this height directly, and it differs from orthometric height by the geoid undulation.

Height of a point above the geoid, measured along the curved plumb line. It is the height used for engineering and flood work because water flows according to gravity, not ellipsoid geometry.

The concrete realisation of a geodetic datum through a network of physical stations with precisely determined coordinates, plus the conventions and constants defining how coordinates change over time.

The instant in time to which coordinates in a dynamic reference frame refer. Because tectonic plates move, a coordinate without a stated epoch is ambiguous and must be propagated before use.

A mathematical operation converting coordinates from one reference system to another, for example a Helmert seven-parameter transformation combining three translations, three rotations and a scale factor between two datums.

A model describing the horizontal velocity of tectonic plates, used to propagate coordinates between epochs in a dynamic reference frame or to express them in a fixed plate-fixed frame.

A surveying method in which a series of connected lines is measured for direction and distance and coordinates are computed successively from a known starting point, with closure checked against a known end point.

A resection technique in which an instrument occupies a convenient unknown point and its coordinates are computed from measurements to several known control points, allowing setup wherever visibility is best.

An integrated surveying instrument combining an electronic theodolite for angles, an electronic distance meter, and onboard computing and data storage, used for detail survey and setting out.

The discrepancy between computed and known values when a survey returns to its starting point or a second control point; it is distributed across the observations to assess and improve accuracy.

A statistical method that estimates unknown parameters and observations by minimising the sum of squared weighted residuals, providing the most probable solution and a rigorous basis for assessing precision.

The process of marking on the ground the positions, levels and alignments defined by a design, transferring coordinates and elevations from plans to physical stakes or marks with specified tolerance.

Real-Time Kinematic positioning: a GNSS technique in which a base station sends corrections to a rover so that carrier-phase ambiguities are resolved in real time, giving centimetre-level positions.

The unknown whole number of carrier cycles between the satellite and receiver at signal lock-on. Resolving it correctly converts noisy code pseudoranges into precise carrier-phase positions.

A GNSS correction service using a network of continuously operating reference stations to model atmospheric and orbit errors across an area and deliver corrections to rovers, extending accuracy over long baselines.

Dilution of Precision: a dimensionless measure of how satellite geometry amplifies ranging errors into position error. Low DOP indicates favourable geometry; high DOP indicates poor geometry.

A GNSS error in which signals reach the antenna after reflection from surfaces such as buildings or water, arriving later than the direct signal and biasing pseudorange and carrier-phase measurements.

The determination of the internal geometry of a camera, principally focal length, principal point position and lens distortion parameters, needed to relate image coordinates to camera coordinates.

The position and attitude of a camera at exposure, expressed as three coordinates and three rotation angles, defining the transformation from camera coordinates to object coordinates.

The geometric principle that the perspective centre, an image point and its corresponding ground point lie on one straight line; it underpins the equations used in photogrammetric triangulation and bundle adjustment.

The geometric correction of an image to remove relief displacement and sensor tilt, producing a planimetrically accurate image in which positions can be measured like a map.

A raster representation of terrain elevation on a regular grid, used for orthorectification, visibility analysis, slope computation and hydrological modelling.

A systematic mathematical transformation of positions on the curved Earth onto a flat surface, inevitably introducing distortion of distance, area, shape or direction that must be controlled by choice of projection.

The ratio between a distance on the projection plane and the corresponding distance on the reference surface; it varies across a projected map and differs from the nominal map scale.

The angle at a point between grid north and true north, caused by the projection; it must be applied when converting between grid bearings and astronomical or geodetic azimuths.

The set of rules describing spatial relationships between features, such as adjacency, connectivity and containment, independent of coordinates, used to maintain data consistency and support network analysis.

A representation of geographic features as points, lines and polygons with associated attribute records, storing geometry explicitly and suited to features with discrete boundaries.

A representation of geographic space as a regular grid of cells, each holding a value, suited to continuous phenomena such as elevation, imagery and land cover.

The set of techniques that derive new information from geographic data using location, distance, overlay, proximity and statistical relationships, for example buffering, overlay and hotspot detection.

An auxiliary data structure, such as a quadtree or R-tree, that organises features by their bounding geometry so that spatial queries can be answered without scanning every record.

A database management system extended to store and query geometric data types, supporting spatial indexing and operations while retaining transactional integrity and standard query languages.

Structured descriptive information about a dataset, covering its content, source, accuracy, coordinate system, currency and access conditions, enabling discovery and fitness-for-purpose assessment.

A systematic public inventory of land parcels, recording their geometry, ownership or tenure and value, maintained for taxation, land management and legal security of title.

A defined area of land, usually bounded by surveyed lines, held under a single tenure or ownership and uniquely identified in the cadastral record.

A land registration system in which the state maintains a register of titles and the registered proprietor's title is guaranteed, contrasting with registration of deeds as evidence of transactions.

A durable physical monument placed on the ground to define a parcel corner, whose position and description are recorded in the survey record and which carries legal significance.

The professional obligation of a surveyor to act in the public interest and in the client's interest ahead of personal gain, particularly when certifying boundaries or positions relied upon by others.

The planned and systematic activities, such as independent checks, calibration and documented procedures, that provide confidence that a survey or spatial product meets specified accuracy requirements.