Geodetic control network: Difference between revisions
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[[File:Übersicht der Stationen.PNG|thumb|Network of reference stations used by Austrian Positioning Service (APOS)]] |
[[File:Übersicht der Stationen.PNG|thumb|Network of reference stations used by Austrian Positioning Service (APOS)]] |
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A '''geodetic control network''' (also '''geodetic network''', '''reference network''', '''control point network''', or '''control network''') is a network, often of [[triangle]]s, which are measured precisely by techniques of terrestrial [[surveying]] or by [[satellite geodesy]]. |
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A '''geodetic control network''' is a network, often of [[triangle]]s, that are measured precisely by techniques of ''control surveying'', such as terrestrial [[surveying]] or [[satellite geodesy]]. It is also known as a '''geodetic network''', '''reference network''', '''control point network''', or simply '''control network'''. |
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A geodetic control network consists of stable, identifiable points with published datum values derived from observations that tie the points together.<ref> |
A geodetic control network consists of stable, identifiable points with published datum values derived from observations that tie the points together.<ref> |
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Classically, a control is divided into horizontal (X-Y) and vertical (Z) controls (components of the control), however with the advent of [[satellite navigation]] systems, [[GPS]] in particular, this division is becoming obsolete. |
Classically, a control is divided into horizontal (X-Y) and vertical (Z) controls (components of the control), however with the advent of [[satellite navigation]] systems, [[GPS]] in particular, this division is becoming obsolete. |
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In the U.S., there is a national control network called the [[National Spatial Reference System]] (NSRS).<ref>{{Cite web |title=8. Theme: Geodetic Control {{!}} The Nature of Geographic Information |url=https://www.e-education.psu.edu/natureofgeoinfo/c6_p9.html |access-date=2023-12-31 |website=www.e-education.psu.edu}}</ref> |
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Many organizations contribute information to the geodetic control network.<ref> |
Many organizations contribute information to the geodetic control network.<ref> |
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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]], [[construction]] and [[navigation]]. The scientific discipline that deals with the establishing of coordinates of points in a |
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]], [[construction]] and [[navigation]]. The scientific discipline that deals with the establishing of coordinates of points in a control network is called [[geodesy]]. |
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{{main|Georeferencing}} |
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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. |
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. |
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== |
== Measurement techniques == |
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=== Terrestrial techniques === |
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{{further|Geodesy#Positioning}} |
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==== Triangulation ==== |
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In "classical geodesy" (up to the sixties) control networks were established by [[triangulation]] using measurements of [[angle]]s and of some spare distances. The precise orientation to the [[geographic north]] is achieved through methods of [[geodetic astronomy]]. The principal instruments used are [[theodolite]]s and [[tacheometer]]s, which nowadays are equipped with [[infrared]] distance measuring, [[data base]]s, communication systems and partly by satellite links. |
In "classical geodesy" (up to the sixties) control networks were established by [[triangulation]] using measurements of [[angle]]s and of some spare distances. The precise orientation to the [[geographic north]] is achieved through methods of [[geodetic astronomy]]. The principal instruments used are [[theodolite]]s and [[tacheometer]]s, which nowadays are equipped with [[infrared]] distance measuring, [[data base]]s, communication systems and partly by satellite links. |
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== Trilateration == |
==== Trilateration ==== |
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{{See also|Trilateration}} |
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[[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 |
[[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 were established or updated by using [[trilateration]] more accurate distance measurements than was previously possible and no angle measurements. |
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EDM increased network [[accuracy|accuracies]] up to 1:1 million (1 cm per 10 km; today at least 10 times better), and made surveying less costly. |
EDM increased network [[accuracy|accuracies]] up to 1:1 million (1 cm per 10 km; today at least 10 times better), and made surveying less costly. |
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== Satellite geodesy == |
=== Satellite geodesy === |
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{{Main|Satellite geodesy}} |
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The geodetic use of [[satellite]]s began around the same time. By using bright satellites like [[Echo satellite#Echo 1|Echo I]], [[Echo satellite#Echo 2|Echo II]] and [[Pageos]], global networks were determined, which later provided support for the theory of [[plate tectonics]]. |
The geodetic use of [[satellite]]s began around the same time. By using bright satellites like [[Echo satellite#Echo 1|Echo I]], [[Echo satellite#Echo 2|Echo II]] and [[Pageos]], global networks were determined, which later provided support for the theory of [[plate tectonics]]. |
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Another important improvement was the introduction of [[radio]] and electronic satellites like [[GEOS (satellite)|Geos A]] and B (1965–70), of the [[Transit (satellite)|Transit]] system ([[Doppler effect]]) 1967-1990 — which was the predecessor of GPS - and of [[laser]] techniques like [[ |
Another important improvement was the introduction of [[radio]] and electronic satellites like [[GEOS (satellite)|Geos A]] and B (1965–70), of the [[Transit (satellite)|Transit]] system ([[Doppler effect]]) 1967-1990 — which was the predecessor of GPS - and of [[laser]] techniques like [[LAGEOS]] (USA, Italy) or [[Starlette]] (France). Despite the use of spacecraft, small networks for [[cadastral]] and [[Technology|technical]] projects are mainly measured terrestrially, but in many cases incorporated in national and global networks by satellite geodesy. |
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== Global navigation satellite systems (GNSS) == |
==== Global navigation satellite systems (GNSS) ==== |
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{{See also|Satellite navigation}} |
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| ⚫ | Nowadays, several hundred geospatial satellites are in orbit, including a large number of [[remote sensing]] satellites and [[navigation]] systems like [[GPS]] and [[Glonass]], which was followed by the European [[Galileo (satellite navigation)|Galileo]] satellites in 2020 and China's [[Beidou]] [[constellation]]. |
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| ⚫ | While these developments have made satellite-based geodetic network surveying more flexible and cost effective than its terrestrial equivalent, the continued existence of [[Benchmark (surveying)|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 [[geodynamic]]s are continuously changing the position of all [[continent]]s by 2 to 20 cm per year. Therefore, modern global networks like [[ETRS89]] or [[International Terrestrial Reference System|ITRF]] show not only [[coordinate]]s of their "fixed points", but also their annual [[velocity|velocities]]. |
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| ⚫ | 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 [[Benchmark (surveying)|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 [[geodynamic]]s are continuously changing the position of all [[continent]]s by 2 to 20 cm per year. Therefore, modern global networks like [[ETRS89]] or [[International Terrestrial Reference System|ITRF]] show not only [[coordinate]]s of their "fixed points", but also their annual [[velocity|velocities]]. |
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== See also == |
== See also == |
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* [[Cadastre]] |
* [[Cadastre]] |
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* [[Map]] |
* [[Map]] |
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* [[ED50]] |
* [[ED50]] |
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* [[Geodetic datum]] |
* [[Geodetic datum]] |
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{{Reflist}} |
{{Reflist}} |
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{{Authority control}} |
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[[Category:Civil engineering]] |
[[Category:Civil engineering]] |
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Latest revision as of 14:11, 14 May 2024
 | This article needs additional citations for verification. (August 2016) |
A geodetic control network is a network, often of triangles, that are measured precisely by techniques of control surveying, such as terrestrial surveying or satellite geodesy. It is also known as a geodetic network, reference network, control point network, or simply control network.
A geodetic control network consists of stable, identifiable points with published datum values derived from observations that tie the points together.[1]
Classically, a control is divided into horizontal (X-Y) and vertical (Z) controls (components of the control), however with the advent of satellite navigation systems, GPS in particular, this division is becoming obsolete.
In the U.S., there is a national control network called the National Spatial Reference System (NSRS).[2]
Many organizations contribute information to the geodetic control network.[3]
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, construction and navigation. The scientific discipline that deals with the establishing of coordinates of points in a control network is called geodesy.
Cartography applications
[edit]
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, unit, and geodetic datum.[4]
Measurement techniques
[edit]Terrestrial techniques
[edit]Triangulation
[edit]
In "classical geodesy" (up to the sixties) control networks were established by triangulation using measurements of angles and of some spare distances. The precise orientation to the geographic north is achieved through methods of geodetic astronomy. The principal instruments used are theodolites and tacheometers, which nowadays are equipped with infrared distance measuring, data bases, communication systems and partly by satellite links.
Trilateration
[edit]
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 were established or updated by using trilateration 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
[edit]
The geodetic use of satellites began around the same time. By using bright satellites like Echo I, Echo II and Pageos, global networks were determined, which later provided support for the theory of plate tectonics.
Another important improvement was the introduction of radio and electronic satellites like Geos A and B (1965–70), of the Transit system (Doppler effect) 1967-1990 — which was the predecessor of GPS - and of laser techniques like LAGEOS (USA, Italy) or Starlette (France). Despite the use of spacecraft, small networks for cadastral and technical projects are mainly measured terrestrially, but in many cases incorporated in national and global networks by satellite geodesy.
Global navigation satellite systems (GNSS)
[edit]
Nowadays, several hundred geospatial satellites are in orbit, including a large number of remote sensing satellites and 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 continents by 2 to 20 cm per year. Therefore, modern global networks like ETRS89 or ITRF show not only coordinates of their "fixed points", but also their annual velocities.
See also
[edit]- Cadastre
- Map
- ED50
- Geodetic datum
- GRS80
- History of geodesy
- Survey marker
- Triangulation station
- Trigonometry
References
[edit]- ^ Rear Adm. John D. Bossler. "Standards and Specifications for Geodetic Control Networks". 1984.
- ^ "8. Theme: Geodetic Control | The Nature of Geographic Information". www.e-education.psu.edu. Retrieved 2023-12-31.
- ^ Minnesota Geospatial Information Office. "MSDI Data: Geodetic Control".
- ^ Minnesota Geospatial Information Office. "Plan for GIS implementation". 1997.
