Benchmark (surveying)

Benchmark (surveying)
An Ordnance Survey cut mark in the UK
This article is about the use of bench marks in surveying, for other uses see Benchmark.

The term bench mark, or benchmark, originates from the chiseled horizontal marks that surveyors made in stone structures, into which an angle-iron could be placed to form a "bench" for a leveling rod, thus ensuring that a leveling rod could be accurately repositioned in the same place in future. These marks were usually indicated with a chiseled arrow below the horizontal line.

The term is generally applied to any item used to mark a point as an elevation reference. Frequently, bronze or aluminum disks are set in stone or concrete, or on rods driven deeply into the earth to provide a stable elevation point.

The height of a benchmark is calculated relative to the heights of nearby benchmarks in a network extending from a fundamental benchmark, a point with a precisely known relationship to the level datum of the area, typically mean sea level. The position and height of each benchmark is shown on large-scale maps.

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 concept near sea level known as the geoid). Elevation may be specified as normal height (above a reference ellipsoid), orthometric height, or dynamic height which have slightly different definitions.

Contents

Other types of survey marks

An Ordnance Survey flush bracket

Triangulation points, also known as trig points, are marks with a precisely established horizontal position. These points may be marked by disks similar to benchmark disks, but set horizontally, and are also sometimes used as elevation benchmarks. Prominent features on buildings such as the tip of a church spire or a chimney stack are also used as reference points for triangulation. In the United Kingdom, triangulation points are often set in large concrete markers, which as well as functioning as a triangulation point, have a benchmark set into the side. With the increasing use of GPS and electronic distance measuring devices, the same techniques and equipment are used to fix the horizontal and vertical position of a survey marker at the same moment, and therefore the marks are usually regarded as "fixed in three dimensions".

Agencies responsible for benchmarks

Benchmarks are typically placed ("monumented") by a government agency or private survey firm, and many governments maintain a register of these marks so that the records are available to all. These records are usually in the form of a geographically searchable database (computer or map-based), with links to sketches, diagrams, photos of the marks, and any other technical details.

Government agencies that place and maintain records of benchmarks include:

Image gallery

See also

  • Benchmarking—a recreational activity in which participants search for benchmarks using a handheld GPS receiver.
  • Geoid

External links


Wikimedia Foundation. 2010.

Игры ⚽ Нужна курсовая?

Look at other dictionaries:

  • Benchmark — may refer to: *Benchmark (surveying), a point of reference for a measurement *Benchmark (crude oil), a reference for and discussion of cost and/or pricing of petroleum, such as Brent Crude and West Texas Intermediate in terms of benchmarks based… …   Wikipedia

  • benchmark — This is a busy word with an interesting history and some recent developments. In its original physical meaning it referred to a wedge shaped incision made by surveyors in a vertical surface so that a bracket could be inserted to form a bench or… …   Modern English usage

  • benchmark — enchmark, bench mark ench mark (Surveying) 1. Any permanent mark to which other levels may be referred. such as: (a) A horizontal mark at the water s edge with reference to which the height of tides and floods may be measured. (b) a surveyer s… …   The Collaborative International Dictionary of English

  • benchmark — /ˈbɛntʃmak / (say benchmahk) noun 1. Surveying a point of known elevation, usually a mark cut into some durable material, as stone or a concrete post with a bronze plate, to serve as a reference point in running a line of levels for the… …  

  • Benchmarking (geolocating) — Benchmarking is an activity in which individuals or teams of participants go out and find benchmarks (also known as geodetic control points ). They typically then log their finds online. Like geocaching, the activity has mainly become popular in… …   Wikipedia

  • Henry Gannett — Henry Gannett, M.E.; LL.D. ((August 24, 1846 November 5, 1914) was an American geographer who is described as the Father of the Quadrangle (geography) which is the basis for topographical maps in the United States.LifeHe was born in Bath, Me.,… …   Wikipedia

  • bench mark — benchmark enchmark, bench mark ench mark (Surveying) 1. Any permanent mark to which other levels may be referred. such as: (a) A horizontal mark at the water s edge with reference to which the height of tides and floods may be measured. (b) a… …   The Collaborative International Dictionary of English

  • Economic Affairs — ▪ 2006 Introduction In 2005 rising U.S. deficits, tight monetary policies, and higher oil prices triggered by hurricane damage in the Gulf of Mexico were moderating influences on the world economy and on U.S. stock markets, but some other… …   Universalium

  • Datum (geodesy) — Geodesy Fundamentals Geodesy · …   Wikipedia

  • Dumpy level — Automatic level in use on a construction site Leveler for use by hand …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”