Question
Change Point (CP) in levelling refers to a location where
The correct answer is
both backsight and foresight readings are taken
Change Point in Levelling Explained
A Change Point (CP) in levelling signifies a location where the temporary setup of the levelling instrument is changed. This is necessary to extend the survey line or bypass obstructions.
Key actions at a Change Point:
- A Foresight (FS) reading is taken on the staff held at the CP location from the instrument's prior position.
- The instrument is moved to a new location.
- A Backsight (BS) reading is taken on the staff held at the *same* CP location from the instrument's new position.
This process ensures continuity in elevation calculations across different instrument setups. Taking both BS and FS readings at the CP allows surveyors to accurately determine height differences between points separated by the instrument's relocation.
Therefore, a Change Point is defined by the procedure involving both backsight and foresight readings.
Was this answer helpful?
Important Questions from Levelling Methods
- Which one of the following is the purpose of taking a backsight observation in levelling?
- The observations of a reciprocal levelling operation carried out from two stations A and B are given in table. It is known that the instrument has collimation error. The correct staff reading over station B when the instrument is set very near to station A is ________ m (Rounded off to three decimal places).
Assume all other errors are negligible.Staff readings at station Instrument set very near to station A (m) B (m) A 1.275 2.005 B 1.040 1.660 - A level with the height of the instrument being 2.550 m has been placed at a station having a Reduced Level (RL) of 130.565 m. The instrument reads 3.665 m on a levelling staff held inverted at the bottom of a bridge deck. The RL of the bottom of the bridge deck is __________ m (rounded off to 3 decimal places).
- In levelling between two points P and Q on opposite banks of a river, the level was set up near P, and the staff reading on P and Q were 2.165 m and 3.810 m, respectively. The level was then moved and set up near Q and the respective staff readings on P and Q were 0.910 m and 2.355 m. The true difference of level between P and Q is __________ m (rounded off to 3 decimal places).
- At a fixed instrument location in levelling, if the backsight reading at a point P is more than the foresight reading at a point Q, then
Need Expert Advice?
