LESSION 2

1. Where is triangulation employed?

Triangulation is employed extensively as a means of control for topographic and similar surveys.

2. What does a triangulation system consist of?

A triangulation system consists of a series of triangles in which one or more sides of each triangle are also sides of adjacent triangles.

3. What do the lines of a triangulation system form?

The lines of a triangulation system form a network tying together the points or stations at which the angles are measurement.

4. Where are the triangulation stations located?

The vertices of the triangles are the triangulation stations.

5. What is avoided by the use of the triangulation method?

By the use of the triangulation method, the necessity of measuring the length of every line is avoided.

6. Why should the lengths of the two or more lines in each system be measured?

Because unavoidable errors in the field measurement, so the lengths of the two or more lines in each system should be measured as a means of checking the computed distances.

7. How are the lines whose lengths are measured called?

The lines whose lengths are measured are called based lines.

8. What is known in geometrical figure offorded by the arrangement of the triangles?

The theoretical value of the sum of included angles is known.

9. What should the lengths of the sides in any triangle be proportional to?

The lengths of the sides in any triangle should be proprotional to the sines of the angles opposite.

10. Why is it not necessary to measure every angle in a triangulation system?

Because the third can be readily computed.

11. Why are all the angles measured?

Because measure all angles permit the application of the known conditions as a measure of the precision of the measurements, or as a means of adjusting the errors.

12. When planning the scheme, what should one keep in mind?

When planning the scheme, certain considerations should be kept in mind, which may be summarized as follows:

a, Every stations should be visible from the adjacent stations. Rays passing close to either the ground or to an obstacle should be avoided since they can be refracted due to air temperature diffirence.

b, The triangles formed thereby should be well-conditioned, that it to say, as nearly equilateral as possible. No angles should be less than 300, if at all possible. That scheme should be kept as simple as possible, but with sufficient redundant observations to provide the necessary checks and to increase precision.

c, The size of the triangles will depend on the configuration of the land, but they should normally be as large as possible compatible with the distinct bisection of signals, having regard to the type of the theodolite used.