Surveying in Architecture (ARCG112)

Quiz Lecture 4 - Introduction to Levelling

Dr. Joao Pinelo Silva, Assistant Professor

Question 1

What does levelling involve?

  1. Measuring vertical distances with reference to the sea level
  2. Measuring vertical distances with reference to the equator
  3. Measuring vertical distances with reference to a vertical plane
  4. Measuring vertical distances with reference to a horizontal plane
  • Remember the definition of levelling?
  • Think about the levelling process as discussed.

Since levelling is finding out the elevation of a point with respect to a datum, what is used as a vertical datum? The aswer is a horizontal plane. The measurement of elevation is done along a vertical (imaginary) line, which is orthogonal to a horizontal plane.
If you are confused about the option that mentions the "sea level", note that it does not refer to the Mean Sea Level (notice the difference when we include the word "mean"). The Mean Sea Level is indeed a type of vertical datum, but that is not what is mentioned.

Question 2

Which of the following are the two pieces of equipment necessary for levelling?

  1. The level and the vertical staff
  2. The map and the level
  3. The lead plumb and the theodolite
  4. The staff and the total station
  • Think about the levelling process that was discussed.
  • What equipment was involved?

The level is used to set a horizontal line of sight. The staff is used to measure the vertical distance between the point being measured and the line of sight.

Question 3

On closing the round on a survey, the surveyor finds the misclosure error.

Why is this error important, and what is the maximum error accepted?

  1. The misclosure error is not important.
  2. It is important to know the magnitude of the misclosure error to know if the survey should be accepted or not, and to eventually fix the error. The maximum allowable error (E) can be calculate by the expression $E = \pm5 \sqrt{n}$mm. Where n = number of times the level was set.
  3. To know if the survey should or not be accepted. $E = \pm5 \sqrt{t}$mm, where t = the maximum delta on the elevations measured.
  4. So that the error can be fixed. $E = \pm5 \sqrt{n}$mm, where n = number of times the level was set.
  • A larger survey is entitled to a larger misclosure error.

It is important to gauge the magnitude of the misclosure error to know if the survey is within the acceptable margin of error, in which case it can be accepted, or outside the margin, in which case the survey should be repeated. It is also important to know the exact error so that, if acceptable, it can be used to fix the measurements. The maximum allowable error (E) can be calculated by the expression $E = \pm5 \sqrt{n}$mm. Where n = number of times the level was set.