A triangulation station, also known as a trigonometrical point, and sometimes informally as a trig, is a fixed surveying station, used in geodetic surveying and other surveying projects in its vicinity. The station is usually set up by a mapping organisation with known coordinates and elevation published. Numerous stations are installed on summits for purposes of visibility and prominence. A graven metal plate on the top of a pillar may provide a mounting point for a theodolite or reflector, often using some form of kinematic coupling to ensure reproducible positioning.
Use Trigonometrical stations form networks of triangulation. Positions of land boundaries, roads, railways, bridges and other infrastructure can be accurately located by the network, a task essential to the construction of modern infrastructure. Apart from the known stations set up by government, some temporary trigonometrical stations are set up near construction sites for monitoring the precision and progress of construction. Some trigonometrical stations use the Global Positioning System for convenience. Its accuracy factors in ionospheric and tropospheric propagation delay errors. Although stations are no longer required for many modern surveying purposes, they remain useful to hikers and even aviators as navigational aids. Particular small triangles on maps (◬) mark summits, for example.
Worldwide The nomenclature for triangulation stations varies regionally: they are generally known as trigonometrical stations or triangulation stations in North America, trig points in the United Kingdom, trig pillars in Ireland, trig stations or trig points in Australia and New Zealand, and trig beacons in South Africa.
Australia In the 1820s, much of New South Wales was unsurveyed territory to the European arrivals. To aid the mapping of the country, the science of trigonometic surveying was introduced by Major Thomas Mitchell who had been brought out to the colony as Assistant Surveyor General of New South Wales. The freestanding peak of Mount Jellore was selected as the first trigonometric summit for his triangulation survey of the countryside. In 1828 Mitchell headed south from Sydney with a small party and camped at the base of the basalt, making daily excursions to the top. While his convict crew cleared the summit of trees, Mitchell plotted and measured distant peaks and sketched the skyline. A national geodetic survey and adjustment carried out in the early 1970s in Australia has left a legacy of trig stations, many consisting of a ground mark with a black quadripod (pyramid frame) supporting a visible disc above the ground mark.
Hong Kong Many trigonometrical stations were placed on hilltops around Hong Kong. They strongly resemble those used in other former British colonial territories such as Australia.
Type A Beacon The most abundant type, consisting of a pillar, height is 1.2-1.3 m tall. The body is white and consists of a black band on top. Has a triangular plate on top.
Type B Beacon A shorter variant of Type A Beacon, at ~0.3 m tall, the pillar is white and the top is black.
Type C Beacon The thicker variant of Type A Beacon, called "肥標" informally by hikers.
Type D Beacon The shorter variant of Type C Beacon, typically lower than 0.8 metres tall.
Type E Beacon A rectangular beacon with a black top, only one installed on Golden Hill, which is modified from a KWW 1902 monument.
Type F Beacon The shorter variant of Type E Beacon, typically ~0.3 m tall, none were built.
Type G Beacon A trapezoidal prism shaped beacon, sometimes referenced as "Old Beacon" by Surveying and Mapping Office, only 2 were built.
Type H Beacon Shorter variant of Type G Beacon, only one were built, on Ha Fa Shan in Tsuen Wan.
Urban Survey Mark (USM) They are small metal fixtures, commonly found on streets, and are also used as reference marks for larger stations.
Picket Boxes Similarly to USMs, they are commonly found on streets. They look like a small circular manhole cover, with the epoxy inside.
Stainless Steel Rod (S/S Rod) They are small concrete bricks, with a stainless steel rod fixed in it, they are used as bench marks.
Others There are many more other types of surveying marks in Hong Kong, such as staples, PVC pipes, or even as simple as a nail.
Classes Trig points and Traverse Stations in HK have a 2 class class system, they can be identified by their numbers.
Trig Points Number less than 100: Class 1 (Except 73.1, 73.2 and 73.3) Number Over 100: Class 2 (Including 73.1, 73.2 and 73.3) Class 2 trig points are also numbered based on their region: 100-199: Hong Kong Island North & Kowloon 200-299: Southwest (Such as Lantau Island) 300-399: New Territories Northwest 400-499: New Territories North 500-599: New Territories South 600-699: New Territories East
Traverse Stations 1XXX.XX, 4XXX.XX, 7XXX.XX: Major Traverse Stations 2XXX.XXX, 3XXX.XXX, 5XXX.XXX, 8XXX.XXX: Minor Traverse Stations
Japan In Japan, there are five classes of triangulation stations (三角点, sankakuten; lit. 'three corner points'):
Class 1 (一等三角点, ittō sankakuten) They are installed approximately every 40 kilometres (25 mi), with smaller ones (as necessary) about every 25 kilometres (16 mi). There are about 1000 throughout Japan. The pillars are 18 centimetres (7.1 in) on a side, and each pillar is anchored with two very large perpendicular rocks buried underground. Class 2 (二等三角点, nitō sankakuten) They are installed approximately every 8 kilometres (5.0 mi). There are about 5000 throughout Japan, and the pillars are 15 centimetres (5.9 in) on a side. Each pillar is anchored with a very large perpendicular rock buried underground. Class 3 (三等三角点, santō sankakuten) There are about 32,000 installed throughout Japan, with one approximately every 4 kilometres (2.5 mi). The pillars are 15 centimetres (5.9 in) on a side, and each pillar is anchored with a large perpendicular rock buried underground. Class 4 (四等三角点, yontō sankakuten) They are installed approximately every 2 kilometres (1.2 mi), and there are about 69,000 throughout Japan. The pillars are 12 centimetres (4.7 in) on a side, and each pillar is anchored with a large perpendicular rock buried underground. Class 5 (五等三角点, gotō sankakuten) These markers were installed in 1899 and are the predecessors to the modern triangulation stations used in Japan today. They are generally not used anymore since the installation of the Class 1-4 stations. Some of them still exist at various locations throughout Japan.
New Zealand
… excerpt ends here. Continue reading the full article.
