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In 1935, the new Director General of the Ordnance Survey, Major-General Malcolm MacLeod, started the retriangulation of Great Britain, an immense task which involved erecting concrete triangulation pillars (trig points) on prominent hilltops throughout Great Britain. 1935 was a common year starting on Tuesday (link will take you to calendar). ...
Image produced from the Ordnance Survey Get-a-map service. ...
The ship wants to know the distance d to the shore. ...
A trig point near Wootton Wawen. ...
The aim was to replace the original triangulation of Britain, known as the Principal Triangulation, which had been performed between 1783 and 1853, with a more modern and accurate triangulation. The Principal Triangulation of Britain was a triangulation project carried out between 1783 and about 1853 at the instigation of the Director of the Ordnance Survey General William Roy (1726-1790). ...
1783 was a common year starting on Wednesday (see link for calendar). ...
1853 was a common year starting on Saturday (see link for calendar). ...
The effort was directed by the cartographer and mathematician Martin Hotine, head of the Trigonometrical and Levelling Division, who planned the operation in a manner similar to a military campaign. Every detail of the operation and measurements were carefully specified in advance to attempt to produce the most accurate measurements possible given the then-current technology.
Erecting new trig points and making measurements frequently required materials and instruments to be carried on foot, up hills and mountains and to isolated islands, in all weathers.
The network of trig points was built and measured between 1936 and 1962, starting with a set of several hundred primary trig points, most of which were placed on high hills so as to be able to link to one another across long distances. In addition, a larger set of roughly 6000 secondary trig points were added to allow the construction of a finer mesh which would extend the reference frame of the primary mesh over shorter distances. 1936 was a leap year starting on Wednesday (link will take you to calendar). ...
1962 was a common year starting on Monday (link will take you to calendar). ...
The results of the retriangulation were then used to create the British national grid reference system which would be the basis of the Ordnance Survey's new maps. The British national grid reference system is a system of geographic grid references commonly used in Great Britain, different from using latitude or longitude. ...
The coordinate system generated by the retriangulation represented a triumph of the available technology at the time, and was accurate to roughly 20 metres from end to end of the country. However, it has now been rendered obsolete by satellite-based GPS measurements, which can obtain a precision of 15 mm from end-to-end, with re-measurements taking hours rather than years. As a result of this, the trig point network is no longer actively maintained, except for a few trig points that have been reused as part of the Ordnance Survey's National GPS Network. Over fifty GPS satellites such as this NAVSTAR have been launched since 1978. ...
See also It has been suggested that Geodetic datum be merged into this article or section. ...
A frame of reference in physics is a set of axes which enable an observer to measure the aspect, position and motion of all points in a system relative to the reference frame. ...
The ship wants to know the distance d to the shore. ...
Further reading - Ordnance Survey 1967. The history of the retriangulation of Great Britain 1935-1962. HMSO, London.
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