In the United Kingdom, triangulation points are often set in large concrete markers that, as well as functioning as triangulation points, have a benchmark set into the side. Prominent features on buildings such as the tip of a church spire or a chimney stack are also used as reference points for triangulation. These points may be marked by disks similar to benchmark disks, but set horizontally, and are also sometimes used as elevation benchmarks.
Triangulation points, also known as trig points, are marks with a precisely established horizontal position.
Other types of survey marks An Ordnance Survey flush bracket Elevation may be specified as normal height (above a reference ellipsoid), orthometric height, or dynamic height which have slightly different definitions. The terms "height" and " elevation" are often used interchangeably, but in many jurisdictions, they have specific meanings "height" commonly refers to a local or relative difference in the vertical (such as the height of a building), whereas "elevation" refers to the difference from a nominated reference surface (such as sea-level, or a mathematical/geodetic model that approximates the sea level known as the geoid). The position and height of each benchmark are shown on large-scale maps. A fundamental benchmark is a point with a precisely known relationship to the vertical datum of the area, typically mean sea level. The height of a benchmark is calculated relative to the heights of nearby benchmarks in a network extending from a fundamental benchmark.
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