20 terms and definitions for Geomatics engineering

Hi, this is some useful terms and definitions for the sudent who study the same field of study than me. I study Geomatics engineering in Ahuntsic College and I really love this. Those 20 terms will help you with the commun language used in class and on your working environment.

Geographic Coordinate System (GCS)

A 2D coordinate system defined by latitude and longitude, based on a reference ellipsoid approximation of the earth. Latitude and longitude are based on the angle from the equator and prime meridian respectively.

Benchmark

A brass or bronze disk set in a concrete base or other permanent structure, inscribed with a mark showing its elevation above or below an adopted vertical datum.

Datum

In geomatics, a mathematical model used to approximate the size and shape of the earth. Different datums might be more appropriate (better approximations) for different locations on the earth. WGS84 is the datum currently used by GPS satellites to determine their position. NAD83 is the most commonly used datum in North America.

Digital Elevation Model (DEM)

Digital Elevation Model. The representation of continuous elevation values over a topographic surface by a regular array of z-values, referenced to a common datum; typically used to represent terrain relief.

Draping

A 2D image superimposed on a 3D surface. For example, an aerial photograph might be draped over a DEM to create a realistic terrain visualisation.

Geocentric datum

A horizontal geodetic datum based on an ellipsoid that has its origin at the earth's centre of mass (e.g., WGS84, NAD83)

Geodetic datum

A datum that is the basis for calculating positions on the earth's surface or heights above and below the earth's surface.

Geoid

The equipotential surface that coincides with the mean ocean surface of the earth. A smooth but highly irregular surface, known by gravitational measurements, to which the force of gravity is everywhere perpendicular.

Interpolation

The estimation of surface values at un-sampled points base on known surface values of surrounding points.

Inverse Distance Weighted (IDW) interpolation

An interpolation technique that estimates cell values in a raster from a set of sample points that have been weighted so that the farther a sampled point is from the cell being evaluated, the less weight it has in the calculation of the cell's value.

NAD83

North American Datum 1983. A horizontal datum based on different spheroid definitions (mathematical model) than WGS84. Although WGS84 and NAD83 often give similar location estimates, NAD83 is a better approximation of true locations in North America.

Nadir

The point that falls directly below (-90°) an observer; a line drawn directly through an observer to the centre of the earth

Photogrammetry

One of the earliest remote sensing techniques, which derives information about the earth from aerial photographs. 3D coordinates of earth features can be determined via stereoscopy (triangulation from two offset images of a similar location).

Projected Coordinate System

A method used to represent the curved, 3D surface of the earth on a 2D plane. Essentially, the conversion of location data from a sphere approximation to a planar surface (e.g., UTM).

Reference Ellipsoid

Since the earth is not a perfect sphere, this is a 3D ellipse used to approximate the shape of the earth. GPS satellites currently reference their position (height) to the reference ellipsoid WGS84. One result of using a reference ellipsoid is that at sea level elevation might not always be recorded as 0.

Registration

To align two or more maps so that equivalent geographic coordinates coincide. Or, to link map coordinates to ground control points.

Survey monument

An object, such as a metal disk, permanently mounted in the landscape to denote a survey station.

Zenith

The point that falls directly above an observer; opposite the nadir and pointing directly away from the centre of the earth.

WGS84

World Geodetic System 1984. The most commonly used geocentric datum and geographic coordinate system today. GPS measurements are based on the WGS84 reference ellipsoid.

GPS

Global Positioning System. A system of radio-emitting and -receiving satellites used to determine positions on the earth. Orbiting satellites transmit signals that allow a GPS receiver to calculate its own location through trilateration (determining position with respect to two other points by measuring the distance between all three points).

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