A brief history of Land Surveying - page 2

Colonial Surveying; Compass and chain:

From colonial times, through the 1800’s, surveying in this country was performed using a crude transit or a compass and a “chain”. The most common surveyor’s chain was 66 feet long and made up of 100 links. 1 link is equal to 1/100 of a chain or 7.92 inches. These units of measurement can still be found in many older deeds on record at the courthouse. The modern steel and fiberglass measuring tapes used by surveyors are still referred to as “chains” in deference to these early methods of surveying. Other early units of measurement were called “rods” or “poles”, representing 16.5 feet for each unit. The compass was either mounted on a tripod or a single pole, called a “Jacob’s Staff”. These early surveying tools were not very precise, but were sufficient in the days when land values were 50 cents per acre, or less.

Transit and tape:

Eventually, the use of the compass gave way to the transit, and the chain to the steel tape. While the compass was generally only able to measure the magnetic bearing of a line to the nearest one-quarter degree, a transit is able to measure the angles between lines to less than one minute of arc. The steel tape, usually 100 or 200 feet long and graduated in hundredths of a foot, provided an accuracy significantly greater than the Gunter’s Chain. The transit and tape permitted the more precise measurements necessary in land subdivision planning, construction surveying, and nearly all boundary or land title surveys. Until recently, this method was used for most surveying work.

Transit and stadia:

Angles were measured with a transit and distances “measured” by optical methods. A rod or “Stadia Board” was graduated in hundredths of a foot, and horizontal cross hairs in the telescope of a transit, called Stadia Hairs, were positioned so that, based on trigonometry, at a distance of 100 feet the stadia hairs subtended exactly one foot on the rod. Thus, within about 500 feet, a distance could be “read” directly from the rod. Due to its speed and efficiency, this method was most common for topographic mapping. For the most part, stadia has also given way to electronic instruments.

Modern Methods of Surveying

Theodolite and electronic distance measurement:

There are no exact standards differentiating an instrument referred to as a “Transit” from one that is referred to as a “Theodolite”. Generally, a theodolite is a much more precise instrument. Some can measure an angle to within 1/10 of one second of arc (one thousandth of a foot in one mile), but 1-second or 3-second theodolites are typical. Also, the angles on a transit were read off of a circular metal plate, graduated in degrees and minutes, while the theodolite replaced the metal plate with an internal etched glass plate and the ability to read an angle through the eyepiece via a series of mirrors and lenses.

By the 1970’s, relatively small, lightweight and easy-to-use electronic distance measuring devices, called EDM’s were in use. They were mounted on the theodolite, and operated on the principle of transmitting a narrow beam of infrared light to a reflector and measuring the time it takes to return.

Before long, the advance of technology and miniaturization of electronic components enabled the building of theodolites that measure angles electronically, measure distances with their own internal EDM, and display a variety of data on an LCD screen. These super-theodolites are referred to as “Electronic Total Stations”. In addition to enhanced speed and accuracy, the digital data can be automatically “downloaded” to an electronic data collector for transfer directly to computers for calculations or CAD drafting. In addition to the speed and accuracy that they provide, the decreasing cost of the electronic total stations has allowed them to virtually totally replace all previous methods and instruments for most survey work. Modern Total Station Pictured at left.

The first GPS satellite was called GPS Block I. Launched in 1978, it was a developmental satellite. Another nine Block I satellites were launched through 1988.

GPS - Global Positioning System

The GPS satellite system (also known as NAVSTAR) was developed by the Department of Defense for obvious reasons. There is presently a nominal operating constellation of 24 satellites. The satellite signals received by the general public are intentionally degraded by the DOD. The system was never meant for civilian use. Some really smart guys figured out a way to use the GPS carrier signal to calculate a receiver's position on the earth in spite of the encryption. This is made possible through the use of two receivers and extremely accurate clocks, used to time the signals received from the satellite vehicles (SV's). The ready availability of these precise clocks make GPS possible. It is now possible to calculate 3 dimensional positions using these receivers at virtually any point on the earth.

GPS does have it's limitations though. The receivers are very expensive, although the price is gradually coming down. And the receivers must have a relatively unobstructed view of the sky. This means that the system is useless indoors, under tree canopies, or in canyon-like locations. Neither can the receivers be used close to buildings or vertical surfaces due to an effect called multipath. Multipath simply means that a receiver gets 2 signals instead of one, due to the reflective properties of a vertical surface. Lastly, the available satellites must be in good geometric formation across the sky. If the satellites are "bunched up" near a single location, the data collected will not give adequate results.

Professional Land Systems utilizes GPS for projects that, in our judgment, are appropriate candidates for the technology. One such example is cellular tower sites. The FAA must know the exact location and height of all towers that exceed a certain height, for purposes of air traffic navigation. GPS is the perfect candidate for such an application.

Robotic Surveying Systems

Robotic "one man" surveying systems are now readily available. These are total stations that are remotely controlled by the use of servo-motors. This is still a relatively new and expensive technology to implement. A robotic surveying system costs in the range of 30k dollars. This first robotic total station was made by a company called Geodometer (now known as Trimble Navigation) in 1990.

Current Definition of Surveying in the State of Tennessee (T.C.A. 62-18-102)

"Practice of land surveying" means any service of work, the adequate performance of which involves the application of special knowledge of the principles of mathematics, the related physical and applied sciences, and the relevant requirements of law for adequate evidence to the act of measuring and locating lines, angles, elevations, natural and man-made features in the air, on the surface of the earth, within underground workings, and on the beds of bodies of water for the purpose of determining areas and volumes, for the monumenting of property boundaries, and for the platting and layout of lands and subdivisions thereof, including the topography, drainage, alignment and grades of streets, and for the preparation and perpetuation of maps, records, plats, field notes, records and property descriptions that represent these surveys.