Triangulation surveys are carried out for locating A. Control points for surveys of large areas B. Control points for photogrammetric surveys C. Engineering works, i.e. terminal points of long tunnels, bridge abutments, etc. D. All the above

The correct answer is D. All of the above.

Triangulation is a method of surveying that uses the principles of geometry to determine the position of points on the Earth’s surface. It is a very accurate method of surveying and is used for a variety of purposes, including:

• Locating control points for surveys of large areas. Control points are points whose positions are known with a high degree of accuracy. They are used as reference points for other surveys.
• Locating control points for photogrammetric surveys. Photogrammetry is a method of surveying that uses photographs to create maps and other spatial data. Control points are used to orient the photographs and to ensure that the maps and other data are accurate.
• Locating engineering works, i.e. terminal points of long tunnels, bridge abutments, etc. Engineering works often require a high degree of accuracy in their location. Triangulation can be used to locate these works with a high degree of precision.

Triangulation is a very versatile method of surveying and can be used for a variety of purposes. It is a very accurate method of surveying and is often used for surveys of large areas or for locating engineering works.