HISTORY OF SURVEYING

HISTORY
Surveying is the science and art of measuring distances and angles on or near the surface of the earth. It is an orderly process of acquiring data relating to the physical characteristics of the earth and in particular the relative position of points and the magnitude of areas. Evidence of surveying and recorded information exists from as long ago as five thousand years in places such as China, India, Babylon and Egypt.
Ancient Egyptian surveyors were called harpedonapata (rope-stretcher). They used ropes and knots, tied at pre-determined intervals, to measure distances. The 3-4-5 triangle (later formalized by Pythagoras) was discovered to give a right angle easily by using a rope knotted at distances of 3,4 and 5 units (as below) and shaped (stretched) to form a triangle with a knot at each corner (vertex).


An early instrument for leveling is shown below. It was made from three pieces of wood in the form of an isosceles triangle. A plumb bob suspended from the apex of the frame aligned itself with a notch at the midpoint of the base only when the base was level.

Early Egyptian level

The great Pyramids were presumably laid out using knotted ropes, simple levels and water trough levels for the foundations. The Egyptians used these techniques in the field whilst the Greeks (Pythagoras, Archimedes, Eratosthenes) proved the geometric reasoning behind the principles and demonstrated a clear relationship between mathematics and surveying.

Archimedes (by 250 B.C.) recorded that the circumference of the earth is 30 myriads of stadia (300 000 stadia). Stadia is an ancient Greek measure of a distance of 202 yards, or approximately 185 metres. Eratosthenes supported this notion and by some complicated reasoning and calculations using the summer solstice, the sun, angles of shadows and the known position of two towns Syene and Alexandria (Syene was known to be 5 000 stadia due south of Alexandria), found the circumference of the earth to be 25 000 miles. It is in fact 24 881 miles - not bad!


For leveling the Greeks used a chorobate. Wooden poles were often used for linear measurements.

Roman level (Chorobate)

Navigation skills were needed for exploration. Lodestone (a naturally magnetized rock - magnetite) was first used to locate magnetic north and in time the magnetic compass developed for navigation on land and water. An Englishman, Thomas Digges, used the word theodolite to describe an instrument, graduated in 360 degrees, used to measure angles in the mid-1500's. By 1590 the plane table, credited as the invention of Jean Praetorius, was in use. It remained in similar form until the early 1900's. A telescope attached to a quadrant for measuring angles permitted the development of the surveying procedures of triangulation in the 1660's. Sextants, which are precision instruments made from brass or aluminum, became very useful for ocean navigation where celestial observations were taken to plot a ship's position. Sextants accurately measure angles between celestial objects such as the stars, moon and sun, and the horizon from which calculations of position can be made. They are a sophisticated refinement of earlier instruments (cross-staff, quadrant, octant to name a few). The sextant remains today as a valuable tool for ocean navigation. The first dumpy levels appeared in the first half of the 1700's combining a telescope with a bubble level. In 1831, in Philadelphia, W. J. Young invented the transit which exhibited marvelous improvements in accuracy of surveying methods. It allowed the telescope to revolve (transit) on its axis. This meant that both forward and backward sightings could be accurately taken and by repeating the process errors were minimized.

The military requirements of two world wars provided the motivation for vast improvements in the design of surveying equipment and execution of surveying operations. In the 1950's Electronic Distance Measurement (EDM) largely replaced triangulation methods for distance measurements. Electronic data collection brought many changes to surveying procedures. The transfer of data collected electronically to computer plotting and drawing systems has reduced time and relieved tedious manual drawing work. The scope of surveying has extended beyond land measurement to include environmental concern for such things as water resources, energy requirements, marine exploration, demarcation of boundaries and protection of the environment.

The use of GPS (Global Positioning System) in surveying procedures is the most recent and revolutionary change to impact land measurement. GPS is very accurate, quick and reliable. However, in conversation with practicing surveyors, I discovered that there is trend to keep older mechanical dumpy levels. This is because they can always be relied on, and trusted, when electronic equipment is faulty or fails, to complete the job in hand.


With Regards,

Sebastian

G.M. Technical

Nunes Instruments

645 Hundred Feet Road,

Coimbatore. 641012.

Tamil Nadu

India,

Web: www.nunesinstruments.com

Mail: info@nunesinstruments.com



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