Surveying 4 Flashcards
(18 cards)
What is chainage?
Chainage is a method of measuring distance along a straight line from a starting point, usually marked at 0 meters.
Why is chainage useful in surveying?
It helps create a site framework when high accuracy isn’t needed and is useful for referencing features along a line.
What does BM stand for in levelling?
BM stands for Benchmark – a point with a known elevation.
What is HPC (Height of Plane of Collimation)?
HPC = Benchmark Elevation + Backsight (BS) Reading.
What is a Backsight (BS)?
The first staff reading taken after setting up the instrument, on a known elevation point (BM).
What is a Foresight (FS)?
The final staff reading taken before moving the instrument.
What is an Intermediate Sight (IS)?
Any staff reading taken between BS and FS.
How do you calculate the elevation of a point using the HPC method?
Elevation = HPC – FS or IS reading.
What does the Rise and Fall method calculate?
Changes in elevation between points.
How is a “Rise” identified?
When the next point has a lower staff reading than the previous one.
How is a “Fall” identified?
When the next point has a higher staff reading than the previous one.
How is elevation calculated using Rise and Fall method?
Elevation = Previous Elevation + Rise – Fall.
What are the steps to set up a levelling instrument?
Place tripod, attach instrument, level it using foot screws, and center the bubble.
What is important when reading a levelling staff?
Ensure the staff is vertical, read the crosshair intersection, and classify the reading (BS, IS, FS).
How do you calibrate a level instrument?
Take readings from opposite sides and compare for errors.
What is profile levelling used for?
Collecting elevation data along a line (e.g., road, pipe trench) to plot ground slope.
What is done with profile levelling data?
It’s used to create a ground profile by plotting elevations against distances.
