After reading this article you will learn about the levelling for finding distance above earth, explained with the help of suitable diagrams. Meaning of Levelling: Levelling is the art of finding the relative heights and depths of the objects on the surface of the earth. It is that part of surveying which deals with the measurements in vertical plane. Levelling [...]
There are two methods of working out the reduced levels of the point from the staff readings taken in the field: 1. Height of Instrument or Collimation Method. 2. Rise and Fall Method. 1. Collimation Method: It consists in finding the elevation of the plane of collimation i.e. (H.I.) for every setting of the instrument and then obtaining the reduced [...]
The following are the main sources of error in levelling: 1. Instrumental Errors 2. Errors of Manipulation 3. Errors due to Settlement of Level and Staff 4. Errors due to Natural Causes 5. Common Mistake in Levelling. Source # 1. Instrumental Errors: (i) Imperfect adjustment: The essential requirement in levelling is that the line of collimation must be horizontal when [...]
The following difficulties are commonly met with while levelling: 1. Levelling Across a Hill or a Hollow 2. Levelling Up-Hill or Down-Hill 3. Staff Very Near the Instrument 4. When the Staff-Station is too Low or too High 5. Levelling across a Pond or a Lake 6. Levelling across a River 7. Levelling across Solid Obstruction like a Wall. Difficulty [...]
Sensitiveness or the sensitivity of a level tube is its capability of exhibiting small deviations of the tube from the horizontal. This quality depends mainly upon the radius of curvature of the level tube which may vary from 10 to 300 metres —the larger the radius, the greater the sensitiveness. Sensitiveness is also increased by increase in the length of [...]
For long sights and accurate levelling work, the effects of curvature of the earth and refraction of the line of sight shall have to be taken into consideration. Due to curvature, the points appear to be lower than they actually are; while due to refraction, they appear to be higher than they actually are. The effect of curvature being greater [...]
The permanent adjustments of different level are made to establish the fixed relationships between its fundamental lines: 1. Permanent Adjustments of a Dumpy Level 2. Permanent Adjustments of a Cooke's Reversible Level 3. Permanent Adjustments of a Cushing's Level 4. Permanent Adjustments of the Y-Level 5. Permanent Adjustments of a Tilting Level. 1. Permanent Adjustments of a Dumpy Level: In [...]
The different types of Levelling are: 1. Differential Levelling 2. Check Levelling 3. Precise Levelling 4. Reciprocal Levelling 5. Longitudinal Levelling or Longitudinal Sectioning 6. Cross Levelling 7. Levelling for Giving Levels for Works 8. Barometric Levelling 9. Hypsometry 10. Trigonometrical Levelling. Type # 1. Differential Levelling: It is carried out with the object of determining the reduced levels of [...]