
A geodetic control network (also geodetic network, reference network, control point network, or control network) is a network, often of
triangle
A triangle is a polygon with three edges and three vertices. It is one of the basic shapes in geometry. A triangle with vertices ''A'', ''B'', and ''C'' is denoted \triangle ABC.
In Euclidean geometry, any three points, when non- colli ...
s, which are measured precisely by techniques of terrestrial
surveying
Surveying or land surveying is the technique, profession, art, and science of determining the terrestrial two-dimensional or three-dimensional positions of points and the distances and angles between them. A land surveying professional is ...
or by
satellite geodesy
Satellite geodesy is geodesy by means of artificial satellites—the measurement of the form and dimensions of Earth, the location of objects on its surface and the figure of the Earth's gravity field by means of artificial satellite techniqu ...
.
A geodetic control network consists of stable, identifiable points with published datum values derived from observations that tie the points together.
Classically, a control is divided into horizontal (X-Y) and vertical (Z) controls (components of the control), however with the advent of
satellite navigation
A satellite navigation or satnav system is a system that uses satellites to provide autonomous geo-spatial positioning. It allows satellite navigation devices to determine their location ( longitude, latitude, and altitude/ elevation) to hi ...
systems,
GPS in particular, this division is becoming obsolete.
Many organizations contribute information to the geodetic control network.
The higher-order (high precision, usually millimeter-to-decimeter on a scale of continents) control points are normally defined in both space and time using global or space techniques, and are used for "lower-order" points to be tied into. The lower-order control points are normally used for
engineering
Engineering is the use of scientific method, scientific principles to design and build machines, structures, and other items, including bridges, tunnels, roads, vehicles, and buildings. The discipline of engineering encompasses a broad rang ...
,
construction
Construction is a general term meaning the art and science to form objects, systems, or organizations,"Construction" def. 1.a. 1.b. and 1.c. ''Oxford English Dictionary'' Second Edition on CD-ROM (v. 4.0) Oxford University Press 2009 and ...
and
navigation
Navigation is a field of study that focuses on the process of monitoring and controlling the movement of a craft or vehicle from one place to another.Bowditch, 2003:799. The field of navigation includes four general categories: land navigation, ...
. The scientific discipline that deals with the establishing of coordinates of points in a control network is called
geomatics
Geomatics is defined in the ISO/TC 211 series of standards as the "discipline concerned with the collection, distribution, storage, analysis, processing, presentation of geographic data or geographic information". Under another definition, it ...
or
surveying
Surveying or land surveying is the technique, profession, art, and science of determining the terrestrial two-dimensional or three-dimensional positions of points and the distances and angles between them. A land surveying professional is ...
.
Cartography
After a cartographer registers key points in a digital map to the real world coordinates of those points on the ground, the map is then said to be "in control". Having a base map and other data in geodetic control means that they will overlay correctly.
When map layers are not in control, it requires extra work to adjust them to line up, which introduces additional error.
Those real world coordinates are generally in some particular
map projection
In cartography, map projection is the term used to describe a broad set of transformations employed to represent the two-dimensional curved surface of a globe on a plane. In a map projection, coordinates, often expressed as latitude and longit ...
, unit, and
geodetic datum
A geodetic datum or geodetic system (also: geodetic reference datum, geodetic reference system, or geodetic reference frame) is a global datum reference or reference frame for precisely representing the position of locations on Earth or other p ...
.
[
Minnesota Geospatial Information Office]
"Plan for GIS implementation"
1997.
Triangulation
In "classical geodesy" (up to the sixties) control networks were established by
triangulation
In trigonometry and geometry, triangulation is the process of determining the location of a point by forming triangles to the point from known points.
Applications
In surveying
Specifically in surveying, triangulation involves only angle ...
using measurements of
angle
In Euclidean geometry, an angle is the figure formed by two rays, called the '' sides'' of the angle, sharing a common endpoint, called the '' vertex'' of the angle.
Angles formed by two rays lie in the plane that contains the rays. Angles ...
s and of some spare distances. The precise orientation to the
geographic north
True north (also called geodetic north or geographic north) is the direction along Earth's surface towards the geographic North Pole or True North Pole.
Geodetic north differs from ''magnetic'' north (the direction a compass points toward the ...
is achieved through methods of
geodetic astronomy. The principal instruments used are
theodolites and
tacheometers, which nowadays are equipped with
infrared
Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from aroun ...
distance measuring,
data bases, communication systems and partly by satellite links.
Trilateration
Electronic distance measurement (EDM) was introduced around 1960, when the
prototype instruments became small enough to be used in the field. Instead of using only sparse and much less accurate distance measurements some control networks was established or updated by using
trilateration Trilateration is the use of distances (or "ranges") for determining the unknown position coordinates of a point of interest, often around Earth ( geopositioning).
When more than three distances are involved, it may be called multilateration, for ...
more accurate distance measurements than was previously possible and no angle measurements.
EDM increased network
accuracies up to 1:1 million (1 cm per 10 km; today at least 10 times better), and made surveying less costly.
Satellite geodesy
The geodetic use of
satellite
A satellite or artificial satellite is an object intentionally placed into orbit in outer space. Except for passive satellites, most satellites have an electricity generation system for equipment on board, such as solar panels or radioiso ...
s began around the same time. By using bright satellites like
Echo I,
Echo II Echo II or Echo 2 or ''variant'', may refer to:
* ''Echo II''-class submarine of the Soviet Navy
* Echo 2 (satellite), a 1964 NASA communications satellite
* Echo II (expansion card), a speech synthesizer card for the Apple II
See also
* EchoSt ...
and
Pageos
PAGEOS (PAssive Geodetic Earth Orbiting Satellite) was a balloon satellite which was launched by NASA in June 1966.
Design
PAGEOS had a diameter of exactly , consisted of a thick mylar plastic film coated with vapour deposited aluminium en ...
, global networks were determined, which later provided support for the theory of
plate tectonics
Plate tectonics (from the la, label= Late Latin, tectonicus, from the grc, τεκτονικός, lit=pertaining to building) is the generally accepted scientific theory that considers the Earth's lithosphere to comprise a number of large t ...
.
Another important improvement was the introduction of
radio
Radio is the technology of signaling and communicating using radio waves. Radio waves are electromagnetic waves of frequency between 30 hertz (Hz) and 300 gigahertz (GHz). They are generated by an electronic device called a transm ...
and electronic satellites like
Geos A and B (1965–70), of the
Transit
Transit may refer to:
Arts and entertainment Film
* ''Transit'' (1979 film), a 1979 Israeli film
* ''Transit'' (2005 film), a film produced by MTV and Staying-Alive about four people in countries in the world
* ''Transit'' (2006 film), a 2006 ...
system (
Doppler effect
The Doppler effect or Doppler shift (or simply Doppler, when in context) is the change in frequency of a wave in relation to an observer who is moving relative to the wave source. It is named after the Austrian physicist Christian Doppler, ...
) 1967-1990 — which was the predecessor of GPS - and of
laser
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word "laser" is an acronym for "light amplification by stimulated emission of radiation". The firs ...
techniques like
Lageos (USA) or
Starlette (F). Despite the use of spacecraft, small networks for
cadastral and
technical
Technical may refer to:
* Technical (vehicle), an improvised fighting vehicle
* Technical analysis, a discipline for forecasting the future direction of prices through the study of past market data
* Technical drawing, showing how something is co ...
projects are mainly measured terrestrially, but in many cases incorporated in national and global networks by satellite geodesy.
Global navigation satellite systems (GNSS)
Nowadays, several hundred geospatial satellites are in orbit, including a large number of
remote sensing
Remote sensing is the acquisition of information about an object or phenomenon without making physical contact with the object, in contrast to in situ or on-site observation. The term is applied especially to acquiring information about Ear ...
satellites and
navigation
Navigation is a field of study that focuses on the process of monitoring and controlling the movement of a craft or vehicle from one place to another.Bowditch, 2003:799. The field of navigation includes four general categories: land navigation, ...
systems like
GPS and
Glonass, which was followed by the European
Galileo satellites in 2020 and China's
Beidou constellation.
While these developments have made satellite-based geodetic network surveying more flexible and cost effective than its terrestrial equivalent for areas free of tree canopy or urban canyons, the continued existence of
fixed point networks is still needed for administrative and legal purposes on local and regional scales. Global geodetic networks cannot be defined to be fixed, since
geodynamics are continuously changing the position of all
continent
A continent is any of several large landmasses. Generally identified by convention rather than any strict criteria, up to seven geographical regions are commonly regarded as continents. Ordered from largest in area to smallest, these seven ...
s by 2 to 20 cm per year. Therefore, modern global networks like
ETRS89 or
ITRF show not only
coordinate
In geometry, a coordinate system is a system that uses one or more numbers, or coordinates, to uniquely determine the position of the points or other geometric elements on a manifold such as Euclidean space. The order of the coordinates is si ...
s of their "fixed points", but also their annual
velocities.
See also
*
Cadastre
*
Maps
*
ED50
*
Geodetic datum
A geodetic datum or geodetic system (also: geodetic reference datum, geodetic reference system, or geodetic reference frame) is a global datum reference or reference frame for precisely representing the position of locations on Earth or other p ...
*
GRS80
*
History of geodesy
The history of geodesy deals with the historical development of measurements and representations of the Earth. The corresponding scientific discipline, ''geodesy'' ( /dʒiːˈɒdɪsi/), began in pre-scientific antiquity and blossomed during the ...
*
Survey marker
*
Triangulation station
*
Trigonometry
References
{{Authority control
Civil engineering
Geodetic surveys
Surveying and geodesy markers