Engineer Surveying Geo-Spatial Information flashcards

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

Geoid undulation

The separation between the geoid and the reference ellipsoid, denoted N; it relates ellipsoidal height h to orthometric height H by h = H + N.

Deflection of the vertical

The angle between the ellipsoid normal and the geoid normal at a point, with meridian and prime vertical components; it affects astronomic and geodetic coordinate comparisons.

Curvature and refraction correction

For a horizontal sight, the combined correction is approximately 0.0675 d² (d in meters, result in meters), where d is the sight distance; it accounts for Earth curvature and atmospheric refraction.

Traverse linear misclosure

The distance between the computed and known endpoint of a traverse, calculated as the square root of the sum of squared easting and northing misclosures; relative precision is misclosure divided by total length.

Danger circle

In three-point resection, the circle through the three known points; if the unknown point lies on or near this circle, the resection solution is weak or indeterminate.

PDOP

Position Dilution of Precision, a measure of satellite geometry quality; computed as the square root of the sum of squared HDOP and VDOP; lower values indicate better geometry for positioning.

RTK

Real-Time Kinematic GNSS positioning uses carrier-phase measurements and a data link from a base station to provide centimeter-level accuracy in real time within about 10–20 km of the base.

Ground sample distance

The distance on the ground represented by one pixel in a digital image; calculated as (pixel size × flying height) / focal length; smaller GSD means higher spatial resolution.

Two-peg test

A field procedure to check a level's collimation error; it compares staff readings at equal and unequal distances and determines whether the line of sight is truly horizontal.

Inverse distance weighting

A deterministic spatial interpolation method that estimates unknown values as a weighted average of nearby known points, with weights inversely proportional to distance raised to a power.

Kriging

A geostatistical interpolation method that uses a variogram model to estimate values and provides a measure of prediction variance; it is a best linear unbiased estimator under certain assumptions.

Spatial join

A GIS operation that appends attributes from one feature layer to another based on a spatial relationship (e.g., intersects, contains, within); it does not alter the geometry of either layer.

Topology rule

A constraint in a geodatabase that defines spatial relationships between features, such as must not overlap or must not have gaps; violations are identified during validation and must be corrected.

Relief displacement

The radial displacement of an object's image from the nadir point in a vertical photograph due to its height above the datum; calculated as d = r × h / H.

Orthophoto

An aerial or satellite image that has been geometrically corrected using a digital elevation model to remove relief displacement and tilt, providing a uniform scale like a map.

NDVI

Normalized Difference Vegetation Index, calculated as (NIR − Red) / (NIR + Red); values range from −1 to 1, with higher values indicating healthier and denser vegetation.

Confusion matrix

A table used in image classification accuracy assessment that cross-tabulates classified and reference classes; overall accuracy, producer's accuracy, and user's accuracy are derived from it.

UTM zone

A 6-degree-wide longitudinal zone in the Universal Transverse Mercator system; there are 60 zones, each with a central meridian scale factor of 0.9996 and a false easting of 500,000 meters.

Conformal projection

A map projection that preserves local angles and shapes of small areas; meridians and parallels intersect at right angles; examples include Mercator and Transverse Mercator.

Grid convergence

The angle between grid north and true north at a point on a map projection; it varies with position within the projection zone and must be applied when converting between grid and geodetic azimuths.

Tissot's indicatrix

A small circle drawn on a map projection to show the distortion of scale; its shape and size indicate conformality and area distortion at that location.

Adverse possession

A legal doctrine by which a person can acquire title to land through actual, open, notorious, exclusive, hostile, and continuous possession for a statutory period.

Riparian boundary

A boundary between land and a water body; for non-navigable waters it typically follows the ordinary high water mark; accretion and reliction change the boundary gradually, while avulsion does not.

Public Land Survey System

A rectangular system used in the United States to divide land into townships (6 miles square) and sections (1 mile square, 640 acres); boundaries are referenced to principal meridians and base lines.

Metes and bounds

A boundary description method that defines a parcel by courses (bearings) and distances from a point of beginning, often following natural or artificial monuments.

ISO 19115

An international standard for geographic information metadata; it defines the schema required to describe spatial datasets, including identification, quality, spatial reference, and distribution information.

EPSG code

A standardized numerical identifier for a coordinate reference system, datum, or unit; for example, EPSG:4326 denotes WGS 84 geographic coordinates and EPSG:32633 denotes UTM zone 33N.

Positional accuracy RMSE

Root mean square error, a measure of positional accuracy computed from the differences between measured and reference coordinates; it is often reported at the 95% confidence level.

Lineage

A data quality element that documents the source materials and processes used to create a dataset; it is part of metadata and supports reproducibility and quality assessment.

Standard of care

The degree of care and skill ordinarily exercised by reputable surveyors under similar circumstances; a surveyor who fails to meet this standard may be liable for negligence.

Responsible charge

The supervision and control of surveying work by a licensed surveyor who is accountable for the work's accuracy and compliance with standards and regulations.

InSAR

Interferometric Synthetic Aperture Radar, a remote sensing technique that uses phase differences between SAR images to measure ground deformation with millimeter to centimeter precision over large areas.