﻿ From the History of Geodetic Tools ﻿

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# From the History of Geodetic Tools

There is some evidence that, in addition to a marked cord, wooden rods were used by the Egyptians for distance measurement. They had the groma, which was used to establish right angles. It was made of a horizontal wooden cross pivoted at the middle and supported from above. From the end of each of the four arms hung a plumb bob. By sighting along each pair of a plumb bob cords in turn, the right angle could be established.

There is no record of any angle-measuring instruments of that time, but there was a level, consisting of a vertical wooden A-frame with a plumb bob supported at the peak of the A so that its cord hung past an indicator on the horizontal bar.

The Greeks used a form of a log line for recording the distances run from point to point along the coast while making their slow voyages from the Indus to the Persian Gulf about 325 BC. The magnetic compass was brought to the West by Arab traders in the 12th century AD. The astrolabe was introduced by the Greeks in the 2nd century BC.

During their occupation of Egypt, the Romans acquired Egyptian surveying instruments, which they improved slightly and to which they added the water level and the plane table.

The water level consisted of a through or a tube turned upward at the ends and filled with water. At each end there was a sight made of crossed horizontal and vertical slits. In laying out their great road system, the Romans are said to have used the plane table. It was the first device capable for recording angles.

Plane tables were in use in Europe in the 16th century, and the principle of graphic triangulation and intersection was practiced by surveyors. In 1620 the English mathematician Edmund Gunter developed a surveying chain, which is also called Gunter’s chain. It is still widely used in English-speaking countries. Gunter’s chain is exactly 22 yards (about 20 m) long and divided into 100 links. In the device each link is a solid bar. Measurement of the public land systems of the United States and Canada is based on Gunter’s chain. An area of 10 square chains is equal to one acre.

The study of astronomy resulted in the development of angle-reading devices. With the publication of logarithmic tables in 1620, portable angle-measuring instruments came into use. They were called topographic instruments, or theodolites. The vernier, an auxiliary scale permitting more accurate readings (1631), the micrometer microscope (1638), telescopic sights (1669), and spirit levels (about 1700) were all incorporated in theodolites.

By the late 18th century modern surveying can be said to have begun. Many improvements and refinements have been incorporated in all the basic surveying instruments. These have resulted in increased accuracy and speed of operations. In addition to modification of existing instruments, two revolutionary mapping and surveying changes have been introduced: photogrammetry, or mapping from aerial photographs (about 1920), and electronic distance measurement (in the 1960s).

2. Answer the following questions:

1) What instruments were used by the Egyptians for distance and angle measurement?

2) What was the groma made of?

3) What could be established with the groma?

4) What did the Greeks use for recording the distance?

5) Who acquired and improved Egyptian instruments?

6) What instruments were added by the Romans?

7) What did the water level consist of?

8) What was the first device capable for recording angles?

9) When and by whom was a surveying chain developed?

10) What instruments came into use in the 17th century?

11) When can modern surveying be said to have begun? Why?

3. Decide, whether the statements are true or false:

1) Wooden rods were used by the Egyptians for angle measurement.

2) The Greeks used for recording the distance a theodolite.

3) The magnetic compass was brought to the West by Arab traders in the 12th century BC.

4) The water level was added by the Romans.

5) The water level was the first device for recording angles.

6) The principle of triangulation and intersection was practiced by surveyors in the 16th century.

7) Gunter’s chain is still widely used in Russia.

8) Gunter’s chain is exactly 22 yards (about 20 m) long and divided into 100 links.

9) An area of 10 square chains is equal to two acres.

10) The study of astronomy didn’t result in the development of angle-reading devices.

11) Modern geodetic instruments have resulted in increased accuracy and speed of operations.

12) Photogrammetry and electronic distance measurement were two revolutionary mapping changes introduced in the 20th century.

4. Name in chronological order when and by whom were different geodetic instruments invented.

Revision

1. Complete the text about the level Ni 002 introduced by Carl Zeiss with the words given below:

Accuracy

Applications

Area

Distance

Geodetic

Height

Horizon

Level

Levelling rod

Precision

Self-aligning

Station

Surveying

Targets

Carl Zeiss introduced the model Ni 002 automatic geodetic 1) ... around 1973, terming it a 2) ... level of maximum 3) ....

When the NI 002 was presented to the 4) ... community in 1973, nobody foresaw that this opened a new chapter in 5) ... levelling. The NI 002 was designed to satisfy the most exacting demands of 6) ... transfer in general. The instrument's well-proven 7) ... of + 0.2 mm/km is achieved by its design concept. The elements provide what is called a "quasi-absolute 8) ...". The mean of the two 9) ... is nearly independent of the 10) ... between instrument and 11) .... With the NI 002 it is possible to carry out precise lines of levels without equalizing backsight and foresight distances to within 10 cm. The greater freedom of instrument stationing is an advantage also in industrial 12) .... Before, precise 13) ... levelling was only possible with relocating the instrument several times, while the NI 002 and its successors can remain at a single 14)..., from which sightings can be taken to 15) ... at different distances.

2. Match the terms with their definitions. Fill in the table below.

a) Angular distance, in degrees, minutes, and seconds of a point north or south of the equator.

b) Angular distance, in degrees, minutes, and seconds, of a point east or west of the Greenwich meridian.

c) Art of obtaining reliable measurements or information from photographs or other sensing systems.

d) Degree of conformity with a standard.

e) Figure of the Earth visualized as a mean sea level surface extended continuously through the continents.

f) Great circle on the surface of the earth passing through the geographical poles and any given point on the Earth's surface.

g) Horizontal direction reckoned clockwise from the meridian plane.

h) Method of extending horizontal position on the surface of the earth by measuring the angles of triangles and the included sides of selected triangles.

i) Method of surveying wherein the lengths of the triangle sides are measured, usually by electronic methods, and the angles are computed from the measured lengths.

j) Monument of material mark or fixed object used to designate a land boundary on the ground.

k) Periodic rise and fall of the water resulting from gravitational interactions between the sun, moon, and earth.

l) Surveying instrument for measuring horizontal and vertical angles.

m) Precision surveying instrument; a theodolite in which the telescope can be reversed in direction by rotation about its horizontal axis.

n) Relatively permanent material object, natural or artificial, bearing a marked point whose elevation above or below an adopted datum is known.

o) Science concerned with the measurement and mathematical description of the size and shape of the earth and its gravitational fields.

p) Sequence of lengths and directions of lines connecting a series of stations, obtained from field measurements, and used in determining positions of the stations

q) Surveying instrument designed for use in the rapid determination of distance, direction, and difference of elevation from a single observation.

r) Surveying operation in which heights of objects and points are determined relative to a specified datum.

s) Tidal datum that is the arithmetic mean of the hourly water elevations.

t) Unit of length equal to 66 feet, used especially in the U.S. public land surveys.

u) Vertical distance of a point above or below a reference surface or datum.

v) An instrument used in surveying to measure the height of distant points in relation to some datum.

 Accuracy Azimuth Benchmark Chain Elevation Geodesy Geoid Landmark Latitude Longitude Surveyor’s level Mean sea level Meridian Photogrammetry Tacheometer Theodolite Tide Transit Traverse Levelling Triangulation Trilateration

3. Sum up information about geodesy, its methods, concepts and the main geodetic instruments. Get ready to tell this information (not less than 20 sentences).

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