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 12^th century AD. The astrolabe was introduced by the Greeks in the 2^nd 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 16^th 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 18^th 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 17^th 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 12^th 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 16^th 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 20^th century.

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