Origins of Surveying

Surveying techniques have existed throughout much of recorded history. In ancient Egypt, when the Nile River overflowed its banks and washed out farm boundaries, boundaries were re-established through the application of simple geometry. The nearly perfect squareness and north-south orientation of the Great Pyramid of Giza, built c. 2700 BC, affirm the Egyptians' command of surveying.

The Egyptian land register (3000 BC).

A recent reassessment of Stonehenge (c.2500 BC) indicates that the monument was set out by prehistoric
surveyors using peg and rope geometry.

Under the Romans, land surveyors were established as a profession, and they established the basic
measurements under which the Roman Empire was divided, such as a tax register of conquered lands (300 AD).

The rise of the Caliphate led to extensive surveying throughout the Arab Empire. Arabic surveyors invented a variety of specialized instruments for surveying, including:

Instruments for accurate levelling: A wooden board with a plumb line and two hooks, an equilateral triangle with a plumb line and two hooks, and a reed level.

  • A rotating alhidade, used for accurate alignment.
  • A surveying astrolabe, used for alignment, measuring angles, triangulation, finding the width of a river, and the distance between two points separated by an impassable obstruction.

In England, The Domesday Book by William the Conqueror (1086)

  • covered all England
  • contained names of the land owners, area, land quality, and specific information of the area's content and habitants.
  • did not include maps showing exact locations

Continental Europe's Cadastre was created in 1808

  • founded by Napoleon I (Bonaparte), "A good cadastre will be my greatest achievement in my civil law", Napoleon I
  • contained numbers of the parcels of land (or just land), land usage, names etc., and value of the land
  • 100 million parcels of land, triangle survey, measurable survey, map scale: 1:2500 and 1:1250
  • spread fast around Europe, but faced problems especially in Mediterranean countries, Balkan, and Eastern Europe due to cadastre upkeep costs and troubles.

A cadastre loses its value if register and maps are not constantly updated.

Large-scale surveys are a necessary pre-requisite to map-making. In the late 1780s, a team from the Ordnance Survey of Great Britain, originally under General William Roy began the Principal Triangulation of Britain using the specially built Ramsden theodolite.

Land Surveys

Cadastral land surveyors are licensed by State governments. In the United States, cadastral surveys are typically conducted by the Federal government, specifically through the Cadastral Surveys branch of the Bureau of Land Management (BLM), formerly the General Land Office (GLO). In the states that have
been subdivided as per the Public Land Survey System (PLSS), the BLM Cadastral Surveys are carried out in accordance with said system. This information is required to define ownership and rights in real property (land, water, mineral, easements, rights-of-way, etc.), to resolve boundary disputes between neighbours, and for any subdivision of land, building development, road boundary realignment, etc.

The aim of cadastral surveys is normally to re-establish and mark the corners of original land boundaries. The first stage is to research relevant records such as land titles (deeds), easements, survey  monumentation (marks on the ground) and any public or private records that provide relevant data.

Monuments are marks on the ground that define location. Pegs are commonly used to mark boundary corners, and nails in bitumen, small pegs in the ground (dumpys) and steel rods are used as instrument locations and reference marks, commonly called survey control. Marks should be durable and long lasting, stable so the marks do not move over time, safe from disturbance and safe to work at. The aim is to provide sufficient marks so some marks will remain for future re-establishment of boundaries. The job of a boundary surveyor retracing a deed or prior survey is to locate such monuments and verify their correct position.

Unfortunately time, development, vandalism and acts of nature often wreak havoc on monuments. The boundary surveyor is often forced to consider evidence peripheral to an actual marker, which may be missing. Fence locations, woodlines, monuments on neighboring property, parole evidence and other evidence is often analyzed.

Examples of typical man made monuments are steel rods, pipes or bars with plastic, aluminum or brass caps containing descriptive markings and often bearing the license number of the surveyor responsible for the establishment of such. The material and marking used on monuments placed to mark boundary corners are often subject to state laws/statutes.

Survey Techniques

Historically, distances were measured using a variety of means, such as chains with links of a known length, for instance a Gunter's chain or measuring tapes made of steel or invar. In order to measure horizontal distances, these chains or tapes would be pulled taut according to temperature, to reduce sagging and slack.

Additionally, attempts to hold the measuring instrument level would be made. In instances of measuring up a slope, the surveyor might have to "break" (break chain) the measurement- that is, raise the rear part of the tape upward, plumb from where the last measurement ended.

Historically, horizontal angles were measured using a compass, which would provide a magnetic bearing, from which deflections could be measured. This type of instrument was later improved upon, through more carefully scribed discs providing better angular resolution, as well as through mounting telescopes with reticles for more precise sighting atop the disc.

Additionally, levels and calibrated circles allowing measurement of vertical angles were added, along with verniers for measurement down to a fraction of a degree- such as a turn-of-the-century transit.

The simplest method for measuring height is with an altimeter - basically a barometer - using air pressure as an indication of height. But for surveying more precision is needed. Toward this end, a variety of means, such as precise levels, have been developed. Levels are calibrated to provide a precise plane from which differentials in height between the instrument and the point in question can be measured, typically through the use of a vertical measuring rod.

With the triangulation method, one first needs to know the horizontal distance to the object. If this is not known or cannot be measured directly, it is determined as explained in the triangulation article. Then the height of an object can be determined by measuring the angle between the horizontal plane and the line through that point at a known distance and the top of the object. In order to determine the height of a mountain, one should do this from sea level (the plane of reference), but here the distances can be too great and the mountain may not be visible. So it is done in steps, first determining the position of one point, then moving to that point and doing a relative measurement, and so on until the mountaintop is reached.

Surveying Equipment

As late as the 1990s the basic tools used in planar surveying were a tape measure for determining shorter distances, a level for determine height or elevation differences, and a theodolite, set on a tripod, with which one can measure angles (horizontal and vertical), combined with triangulation. Starting from a position with known location and elevation, the distance and angles to the unknown point are measured.

A more modern instrument is a total station which is a theodolite with an electronic distance measurement device (EDM) and can also be used for leveling when set to the horizontal plane. Since their introduction, total stations have made the technological shift from being optical-mechanical devices to being fully electronic with an onboard computer and software. Modern top-of-the-line total stations no longer require a reflector or prism (used to return the light pulses used for distancing) to return distance measurements, are fully robotic, and can even e-mail point data to the office computer and connect to satellite positioning systems, such as a Global Positioning System (GPS).

Though real-time kinematic GPS systems have increased the speed of surveying, they are still only horizontally accurate to about 20 mm and vertically accurate to about 30-40 mm.However, GPS systems do not work well in areas with dense tree cover or constructions. Total stations are still used widely, along with other types of surveying instruments.

One-person robotic-guided total stations allow surveyors to gather precise measurements without extra workers to look through and turn the telescope or record data. A faster way to measure large areas (not details, and no obstacles) is with a helicopter, equipped with a laser scanner, combined with a GPS to determine the position and elevation of the helicopter. To increase precision, beacons are placed on the ground (about 20 km apart). This method reaches precisions between 5-40 cm (depending on flight height)

All information found at Wikipedia