computer science

Geodetic control network

Geodetic control network is a computer science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Geodetic control network rather than just read about it. In short: 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.

Key takeaways

Geodetic control network belongs to computer science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Geodetic control network to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Geodetic control network from memory before moving on to harder problems.

Reference excerpt

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 geodetic markers, which are stable, identifiable points or vertices with published coordinate values derived from observations that tie the points together. In the U.S., there is a national control network called the National Spatial Reference System (NSRS). Many organizations may contribute information to the geodetic control network. In the United Kingdom, the Ordnance Survey maintains the OS Net 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, construction and navigation. The scientific discipline that deals with the establishing of coordinates of points in a control network is called geodesy.

Applications

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, unit, and geodetic datum.

Construction and engineering Survey control networks are used for different phases of engineering and construction. Applications, according to the Chartered Institution of Civil Engineering Surveyors, include:

capturing topographic data, construction setting-out, as-built verification, infrastructure maintenance, and deformation monitoring. An example application is the accurate and robust positioning of tunnel boring machines.

Measurement techniques

Terrestrial techniques

Triangulation

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

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.

Levelling

Optical levelling, which determines relative height difference between two points, can be used to determine the vertical component of control networks, particularly relative to fixed datums (such as that employed for Ordnance Datum Newlyn). Double run level techniques may be employed to minimise error.

Satellite geodesy

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)

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 Cadastre Map ED50 Geodetic datum GRS80 History of geodesy Survey marker Triangulation station Trigonometry

References

Illustrations

Worked examples

Example 1 — a first encounter with Geodetic control network

Start with the simplest possible case. Write down what Geodetic control network claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In computer science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Geodetic control network before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Geodetic control network ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Geodetic control network

In research: Geodetic control network appears in computer science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Geodetic control network in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Geodetic control network is common in secondary-school and first-year university syllabi. It links to neighbouring topics Civil engineering, Geodetic surveys, Surveying and geodesy markers, so understanding it makes those chapters shorter.
In everyday life: Look for Geodetic control network outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Geodetic control network in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Geodetic control network means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Geodetic control network out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Geodetic control network in simple terms?

Why does Geodetic control network matter?

Because it connects several computer science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Geodetic control network?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Geodetic control network.