FUNDAMENTAL SURVEYING Leveling & Differential Leveling 3 — Questions and Answers
Question 1: What is 'trigonometric leveling'?
- Leveling using water tubes connected between two points
- Computing elevation differences from measured slope distances and vertical angles (Correct answer)
- A method using only a hand level and stadia rod
- Leveling by averaging many barometric readings
Correct answer: Computing elevation differences from measured slope distances and vertical angles
Trigonometric leveling calculates elevation differences using V = S times sin(vertical angle), where S is the slope distance.
Question 2: Which datum is used as the standard vertical datum in the United States?
- NGVD 29
- NAVD 88 (Correct answer)
- WGS 84
- NAD 83
Correct answer: NAVD 88
NAVD 88 (North American Vertical Datum of 1988) is the current official vertical datum for the US, replacing the older NGVD 29.
Question 3: A Philadelphia rod reads 4.756 ft but is not perfectly plumb. The reading will be:
- Too small
- Too large (Correct answer)
- Exactly correct
- Negative
Correct answer: Too large
A tilted rod appears longer in the line of sight than a plumb rod, so the reading will be erroneously large.
Question 4: What is the purpose of the 'peg test' (two-peg test) for a level instrument?
- To check if the tripod is stable
- To detect and measure collimation error in the line of sight (Correct answer)
- To calibrate the rod interval factor
- To check if the bubble tube is centered
Correct answer: To detect and measure collimation error in the line of sight
The two-peg test determines whether the instrument's line of sight is truly horizontal by comparing readings at equal and unequal distances.
Question 5: In barometric leveling, what relationship is used to estimate elevation?
- The decrease in atmospheric pressure with increasing altitude (Correct answer)
- The relationship between temperature and humidity
- The magnetic variation at different elevations
- The curvature of the Earth at different latitudes
Correct answer: The decrease in atmospheric pressure with increasing altitude
Barometric leveling exploits the fact that atmospheric pressure decreases predictably with altitude, allowing elevation differences to be estimated from pressure readings.
Question 6: A level circuit has a total length of 4 miles and a closure error of 0.06 ft. What is the total distance in feet?
- 21,120 ft (Correct answer)
- 5,280 ft
- 10,560 ft
- 2,640 ft
Correct answer: 21,120 ft
Total distance = 4 miles times 5,280 ft/mile = 21,120 ft, giving a precision of 1:352,000.
FUNDAMENTAL SURVEYING Leveling & Differential Leveling 3
What is 'trigonometric leveling'?