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Ground control

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Ground Control
ground control - [geodesy] A system of points with known positions, elevations, or both, used as fixed references in georeferencing map features, aerial photographs, or remotely sensed images.
[Category=Geospatial ] ...


Ground Control Point
A point in two dimensions which is common to both an image and a topographic map, and can be represented by (X,Y) coordinates based on the map`s cartographic projection and grid system; used in geometric correction of distorted images, ...

Ground Control Stations
Several ground control stations exist for the GPS. The Master Control facility is located at Schriever Air Force Base (formerly Falcon AFB) in Colorado. The control stations use precise RADAR equipment to determine each satellite's location, altitude, and velocity.

Ground Control: Point on the surface of the earth with known coordinates as represented by some geographic grid reference system.

7 Ground control points and OS maps
Of course, if the data are surveyed in from a GPS point, for example, and the co-ordinates are specified in full numeric form (e.g. 312300 445600 from the above example) the OS are not involved.

[edit] ~
The ~ segment of GLONASS is entirely located within former Soviet Union territory. The ~ Center and Time Standards is located in Moscow and the telemetry and tracking stations are in Saint Petersburg, Ternopol, Eniseisk, Komsomolsk-na-Amure.[6] ...

~
~ refers to points on the surface of the earth with known coordinates as represented by some geographic grid reference system.

~ - AUTO TIE
Initially, auto tie points have no xyz values associated with their position. They are used to cross-match features in the stereo-overlap between adjacent images. They can be collected manually (not recommended) or using the auto-tie feature.

~ point(s)
GCRA
Geographic and Cartographic Research and Applications Section ...

~ point(s); Geodetic control point(s)
GCRA
Geographic and Cartographic Research and Applications Section ...

The ~ points may be also (ir)regularly distributed and can be more than four points.
EXAMPLE
Most DXF/DWG drawings are done within XY coordinates. To transform them to a national grid, we can use 'v.transform' with a 4 point transformation ...

What is a ~ Point (GCP)?
Answer:
A precisely known UTM or Geographic coordinate of a point on the earth
used to geolocate the image. GCPs are needed to create absolute geolocated
DEMs. The requestor must supply these points, along with their precise
locations on the 3N and 3B images.

Twenty three ~ points (GCPs) digitized from 7.5 minute USGS topographic quadrangles (USGS quads) were used to rectify the October 5, 1990 SPOT-XS image to a Universal Transverse Mercator (UTM) map projection (RMSE = 0.29 pixels / 5.91 m).

~ Point - GCP: Any point which is recognizable on both remotely sensed images, maps and aerial photographs and which can be accurately located on each of these. This can then be used as a means of reference between maps or, more commonly, between maps and digital images.

Effective photogrammetry makes use of ~ by which aerial photographs are carefully compared and registered to the locations and characteristics of features identified in ground-level surveys.

A system of transmitting satellites and ~ stations that allows someone with a suitable signal receiving and processing device (GPS receiver) to accurately determine their location at any point on or above the earth.

The shape of the great circle on an equidistant cylindrical map is a familiar view in ~ rooms for satellites.

[aerial photography] An aerial photograph or photographs, referenced to a ~ system and overprinted with map symbology.
Reference map
[map design] A map designed to show where geographic features are in relation to each other.

To determine elevation of a place, it must be surveyed, in reference to a ~ point.
Part of a topographic map of Haleakala (Hawaii), showing elevation.
[edit] Topography ...

Photogrammetry uses aerial photographs to produce planimetric and topographic maps of the earth's surface and of features of the built environment. Effective photogrammetry makes use of ~ by which aerial photographs are carefully compared and registered to the locations and ...

These inputs are the following: 1) the unrectified raster image scanned from the diapositive or directly acquired from a digital sensor, 2) a digital elevation model with the same area of coverage as the digital orthophoto, 3) the image and ground coordinates of photo identifiable ~ ...

You can use the Traverse window to enter this into a line layer. It is important that you add this external boundary as accurately as possible, so start your traverse at an existing ~ point or boundary that you believe to be accurate.

system is unknown we may relate the co-ordinate system to a known co-ordinate system on the basis of a set of selected points whose co-ordinates are known in both systems (given in the figure Overview of Coordinate Transformations as direct transformations). These points may be ~ points ...

Or, to link map coordinates to ~ points.Survey monumentAn object, such as a metal disk, permanently mounted in the landscape to denote a survey station.Universal Transverse Mercator (UTM)Universal Transverse Mercator.

Supplemental control points are those needed to relate the aerial photographs used for mapping with the system of ~. These points must be positively photoidentified; that is, the points must be positively correlated with their images on the photographs.

See also: See also: What is the meaning of Location, Map, Information, Image, Control Point?

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