Leveling is the process of making a surface level, even, or flat. Leveling is an art of determining the relative height of different points on, above or below the surface.
Principle of leveling
The principle of leveling is however to obtain horizontal line of sight with respect to which vertical distances of the points above or below this line of sight are found.
Objective of leveling
Therefore, the objective of Leveling are:
- To Find the elevation of given point with respect to some assumed reference line called datum.
- To establish point at required elevation respect to datum.
Types of Leveling in Surveying
- Direct leveling
- Trigonometric leveling
- Barometric leveling
- Stadia leveling
It is the most commonly used method of leveling.In this method, measurements observed directly from leveling instrument.Moreover based on the observation points and instrument positions direct leveling divided into different types as follows:
- Simple leveling
- Differential leveling
- Fly leveling
- Profile leveling
- Precise leveling
- Reciprocal leveling
It is a simple and basic form of leveling in which the leveling instrument placed between the points which elevation is to be find.Therefore Leveling rods placed at that points and sighted them through leveling instrument. It is performed only when the points are nearer to each other without any obstacles.
Differential leveling is performed when the distance between two points is more.In this process, number of inter stations located and instrument shifted to each station and observed the elevation of inter station points. Finally difference between original two points is determined.
Fly leveling is conducted when the benchmark is very far from the work station.In such case, a temporary bench mark is located at the work station which is located based on the original benchmark.Even it is not highly precise it is used for determining approximate level.
Profile leveling generally adopted to find elevation of points along a line such as for road, rails or rivers etc. In this case, readings of intermediate stations taken and reduced level of each station found.From this cross section of the alignment is drawn.
Precise leveling is similar to differential leveling but in this case higher precise wanted.To achieve high precise, serious observation procedure performed. The accuracy of 1 mm per 1 km is thus achieve.
When it is not possible to locate the leveling instrument in between the inter visible points, reciprocal leveling is perform. This case appears in case of ponds or rivers etc. in case of reciprocal leveling, instrument settled nearer to 1st station and sighted towards 2nd station.
The process of leveling in which the elevation of point or the difference between points is measure from the observed horizontal distances and also vertical angles in the field is termed as trigonometric leveling.
In this method, trigonometric relations are used to find the elevation of a point from angle and horizontal distance so, it is termed as trigonometric leveling. It is also termed as indirect leveling.
Therefore Barometer is an instrument use to measure atmosphere at any altitude. So, in this method of leveling, atmospheric pressure at two different points is observe, based on which the vertical difference between two points is determined. In short, it is a rough estimation and used rarely.
First of all, It is a modified form of trigonometric leveling in which Tacheometer principle is use to determine the elevation of point.In this case the line of sight is always incline from the horizontal.It is more accurate and suitable for surveying in hilly terrains