PEC EPE Geoinformatics flashcards

39 cards. Read the term and the definition here. The deck at the top of this page is optional.

Geoid

The equipotential surface of Earth's gravity field that best fits mean sea level; orthometric heights are measured relative to it, and its separation from the ellipsoid is the geoid undulation N.

Ellipsoidal height

The height h of a point above the reference ellipsoid, measured along the ellipsoid normal; it relates to orthometric height H by h = H + N, where N is the geoid undulation.

Datum transformation

A mathematical operation converting coordinates from one geodetic datum to another, using translations, rotations and scale (Helmert) or a grid; accuracy depends on the model and network extent.

ITRF epoch

Because tectonic plates move, ITRF coordinates must be accompanied by a reference epoch; coordinates at another time are obtained by applying a plate-motion model.

Levelling misclosure

The difference between the sum of backsights and foresights along a levelling loop; it is distributed proportionally to distance or number of setups to obtain adjusted heights.

Resection danger circle

The locus of points from which three known control points are seen under a constant angle; a station on this circle gives an indeterminate or ill-conditioned resection solution.

Bowditch rule

A traverse adjustment that distributes the linear misclosure proportional to leg length; suitable for compass traverses where angular and linear errors are comparable.

Curvature and refraction

For long sights, Earth curvature and atmospheric refraction bend the line of sight; the combined correction is approximately 0.0678·D² metres with D in kilometres.

PDOP

Position dilution of precision, a measure of satellite geometry quality; PDOP equals the square root of HDOP squared plus VDOP squared, and lower values indicate better geometry.

RTK positioning

Real-time kinematic GNSS uses carrier-phase observations from a base station or network to resolve integer ambiguities, giving centimetre-level positions within a limited baseline.

Integer ambiguity

The unknown whole number of carrier cycles between satellite and receiver; resolving it to an integer converts phase measurements into centimetre-level positions.

Multipath

GNSS signal reflection from nearby surfaces arriving at the antenna after the direct signal; mitigated by choke-ring antennas, elevation masks and longer observation sessions.

Relief displacement

On a vertical aerial photograph, the radial displacement of an object due to its height: d = r·h/H, where r is radial distance, h object height and H flying height.

Photograph scale

For a vertical aerial photograph, scale equals focal length divided by flying height above ground; on tilted photographs scale varies across the frame.

Orthophoto

An aerial or satellite image geometrically corrected so that tilt and relief displacement are removed; true orthorectification in built-up areas requires a surface model.

NDVI

Normalised Difference Vegetation Index, computed as (NIR − Red)/(NIR + Red); high values indicate healthy vegetation, and the ratio reduces illumination differences.

UTM zone parameters

Universal Transverse Mercator uses 60 zones of six degrees longitude, central meridian scale factor 0.9996, false easting 500,000 m, and false northing 10,000,000 m south.

Conformal projection

A map projection that preserves local angles and shape; scale is the same in all directions at a point, but area is generally distorted, as in Mercator and Transverse Mercator.

Choropleth map

A thematic map shading administrative or statistical areas by a normalised value such as a rate or density; raw counts should not be used because they reflect area size.

Visual variables

Cartographic attributes used to encode data: position, size, shape, value (lightness), colour hue, orientation and texture; each suits different data types and levels of measurement.

Spatial overlay

A GIS operation combining two layers to produce a new layer with combined geometry and attributes; examples include union, intersection, identity, erase and clip.

Buffer operation

A GIS operation creating a polygon at a specified distance around features; fixed, variable and multi-ring buffers are used, and projection distortion affects the result.

Kriging

A geostatistical interpolation method using a fitted variogram model to weight observations by spatial covariance; it provides predicted values and an estimate of prediction variance.

Spatial index

A data structure such as an R-tree, quadtree or grid that speeds up spatial queries by filtering candidate features with bounding boxes before exact geometry tests.

Topology rules

Constraints on spatial data such as no polygon overlap, no gaps, no dangling lines and no self-intersections; enforcing them supports logical consistency and data quality.

Spatial ETL

Extract, transform and load processes for spatial data; they convert formats, reproject coordinates, clean geometry and load results into a target database or GIS.

OGC Simple Features

A standard geometry model with Point, LineString, Polygon and their multi-part and collection forms, plus text and binary encodings and spatial predicates.

WFS versus WMS

WMS returns rendered map images, while WFS returns vector features with attributes that a client can query and analyse; both are OGC web services with capability documents.

Foreign key

A relational database column referencing a primary key in another table; it enforces referential integrity so that related records cannot be orphaned.

Moran's I

A global measure of spatial autocorrelation ranging roughly from −1 to +1; positive values indicate clustering of similar values, negative values indicate dispersion.

Getis-Ord Gi*

A local statistic identifying statistically significant hot spots and cold spots; its result depends on the spatial weights matrix and the analysis scale chosen.

Least-cost path

A route minimising accumulated cost across a friction surface such as slope or land cover; it differs from the Euclidean shortest line between two points.

Torrens title

A land registration system in which the register is conclusive evidence of title and the state guarantees it, subject to statutory exceptions and registered interests.

Accretion versus avulsion

Gradual, imperceptible addition of land by water action (accretion) can shift a riparian boundary, whereas sudden, perceptible change (avulsion) generally does not.

Adverse possession

Acquisition of title by long, open, continuous and unauthorised occupation of another's land for a statutory period, subject to jurisdiction-specific requirements.

Monument precedence

A common boundary-evidence rule: a physical monument marking a corner generally prevails over the recorded distance or coordinate when the two conflict, depending on jurisdiction.

Conflict of interest

A situation where a personal, financial or other interest could improperly influence professional judgement; it must be disclosed and managed, or the work declined.

Critical path method

A scheduling technique identifying the longest sequence of dependent tasks; activities on the critical path have zero float, and delay there delays the whole project.

Limitation of liability

A contract clause capping the professional's financial exposure for errors or omissions; it should be explicit, reasonable and consistent with insurance cover.