Leveling in surveying – Instruments and its Types
The art of determining the relative heights of point on the surface of the earth is term as leveling.
A leveling instruments are “Level” and “Staff” is employ for this purpose along with other equipment. That’s are :-
Instruments for leveling
Level and Leveling Staff
Types of Level
- Dumpy level
- Tilting level
- Wye level
- Automatic level
Dumpy level : The Dumpy level is a simple, compact and stable instrument. The telescope is rigidly fix to its supports. Hence it cannot be rotate about horizontal axis.
Tilting level : It is also known as I.O.P. level (Indian office Pattern).In this level the telescope tilts about its horizontal axis hence it is term as tilting level.
Wye level : The essential difference between wye level and other levels is that in wye level the telescope is carries by two vertical wye supports. The telescope can be rotate, moved or even raise in wyes.
Automatic level : It is also known as self aligning level. It is a recent development. The fundamental difference between auto level and other levels is that the levelling is not manually but it is levelled automatically. It is achieve by inclination compensating device.
Leveling staffs are scales on which these distances are measures by-
Levelling staffs are of two types
- Self Reading staff
- Target staff
Self Reading Staff
The self reading staff can be read directly by the level man looking through the telescope.
• Common types of self reading staffs
- Ordinary staff : The one length staff, is solid and made of season wood, it is 3 m long and graduate in the same way as the telescopic staff.
- Sop-with telescopic staff : Such a staff is arranged in three lengths placed one into the other. It can be extend to its full length by pulling. The top portion is solid and the central box is hollow the total length of staff is 4 m. The staff is graduate in such a way that smallest division is of 5 mm. the value in m are mark in red on the left and those in decimeter are in black on the right.
- Folding Staff : The folding staff is made up of well seasoned timber such as Cyprus. It consists of two 2 m wooden pieces with a joint assembly. Each piece of the staff is made of one longitudinal strip without any joint. The folding joint is of the detachable type with a locking device at the back. The staff is join together in such a way that the staff may be folded from one another when required. The staff has brass cap at the bottom. It has two folding handles, with spring action. It is provides with a circular bubble fit at the back.
For very precise works and sight target staff are use. A movable target is provides in this staff. A vernier is provides on target to give precise reading. In target staff level man directs the staff man to move the target up and down until it bisects by the line of sight. The staff man observe the staff reading