Precautions in Levelling

Keywords: Levelling, precautions, errors in leveling

Since you have acquired a good understanding about leveling, let’s now move on to the last topic in this section.

Levelling has to be done with utmost care to obtain accurate and precise readings. Any error in the readings could possibly harm all the calculation and subsequent surveying processes.

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Difficulties in levelling

Keywords: Levelling, difficulties in levelling, errors in levelling

The last two topics in leveling are the difficulties and precautions to be taken for an error-free levelling process. Let’s jump into the first section, difficulties in levelling.

Some of the difficulties that are commonly encountered in levelling are:

When the staff station is more than 3metres above the line of sight
Solution: Measure the distance (d) from line of sight to the staff placed at the station accurately with a tape.
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Problem of missing entries in the field book

Keywords: Levelling examples, levelling, rise and fall method, missing entries problem

Since we have already studied about levelling, now let’s move on to a specific problem in this section. The problem of missing entries in the field book is an application level problem, often asked in question papers. An example on this type of problem is illustrated as follows:

Problem: The following level readings have been taken from a page of a level book. Some of the readings are missing. It is required to fill all the entries in the page. Fill up the missing readings and apply the arithmetic checks.
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Booking the staff reading and reduction of levels

Keywords: Levelling, reduction of levels, rise and fall methods, height of instrument

In the previous posts we have learned about the leveling, its principles and methods. Now we can move on to a practical illustration of this leveling process.

A level filed book or a level book is used for booking and reducing the levels of various points in a systematic way. There are two methods for reducing the levels namely

  • The height of the instrument method
  • The rise and fall method

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Principle of Levelling

Keywords: Levelling, principle, differential levelling, station, backsight, foresight, intermediate sight, change point, turning point, balancing

Let’s now move on to the basic principle of levelling. If you want to refresh the basic concepts of levelling, you can read them here.

Simple levelling
When the levelling instrument is properly leveled, the bubble tube axis and the line of sight will be horizontal and the vertical axis of the instrument will be vertical. The bubble must be central and traverse. The line of sight will remain in a horizontal plane when the telescope is rotated. Thus if the telescope is sighted towards a staff kept on a point of known elevation, the height or elevation of the line of sight can be determined. If the telescope is now directed to staff kept on points of unknown elevation, the staff readings can be read. From which the reduced levels of the unknown points can be determined.

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