LSIT Measurement Technology 4 — Questions and Answers
Question 1: In GPS surveying, 'PDOP' stands for Position Dilution of Precision. A PDOP of 2 versus a PDOP of 6 means:
- PDOP 2 yields better precision because satellites are more favorably distributed (Correct answer)
- PDOP 6 yields better precision because more satellites are visible
- PDOP has no effect on positional accuracy
- PDOP 2 means fewer satellites are available
Correct answer: PDOP 2 yields better precision because satellites are more favorably distributed
Lower PDOP values indicate better satellite geometry, resulting in more precise position estimates.
Question 2: A leveling rod reading of 4.832 ft is taken at a point 500 ft from the instrument. What combined curvature and refraction correction should be applied?
- Approximately 0.010 ft (negligible for most surveys) (Correct answer)
- Approximately 0.50 ft
- Approximately 0.001 ft
- Approximately 1.00 ft
Correct answer: Approximately 0.010 ft (negligible for most surveys)
Combined curvature and refraction ≈ 0.0206 × d² (miles); at 500 ft (~0.095 mi), correction ≈ 0.0002 ft, which is negligible.
Question 3: What is the purpose of 'balancing in' a level circuit?
- To make backsight and foresight distances equal, minimizing collimation and curvature errors (Correct answer)
- To ensure the rod is held perfectly vertical
- To verify the instrument's compensator is functioning
- To average multiple rod readings at each point
Correct answer: To make backsight and foresight distances equal, minimizing collimation and curvature errors
Equal backsight and foresight distances cancel systematic errors from instrument collimation and Earth curvature.
Question 4: A laser level emits a beam that is 0.003° out of horizontal. At 200 ft, what vertical error does this introduce?
- Approximately 0.010 ft (Correct answer)
- Approximately 0.100 ft
- Approximately 0.001 ft
- Approximately 1.000 ft
Correct answer: Approximately 0.010 ft
Error = 200 × tan(0.003°) ≈ 200 × 0.0000524 ≈ 0.0105 ft ≈ 0.010 ft.
Question 5: Which systematic error in EDM instruments is best detected by measuring over a calibrated baseline of multiple lengths?
- Scale error (cyclic error) (Correct answer)
- Pointing error
- Plumbing error
- Reading error
Correct answer: Scale error (cyclic error)
Cyclic (scale) errors repeat over fixed distance intervals and are revealed by comparing EDM measurements to a known baseline at multiple distances.
Question 6: In a total station traverse, the 'closing error in latitude and departure' is used to:
- Determine the linear misclosure and apply a systematic correction to each leg (Correct answer)
- Set the instrument's horizontal circle to zero at the first station
- Compute the area enclosed by the traverse
- Verify that all interior angles sum to (n–2)×180°
Correct answer: Determine the linear misclosure and apply a systematic correction to each leg
The latitude and departure misclosure defines the linear error of closure, which is then distributed among traverse legs using methods like Compass Rule.
Question 7: What does 'atmospheric correction' to an EDM measurement primarily account for?
- Changes in the speed of light through air due to temperature, pressure, and humidity (Correct answer)
- The physical distance added by the prism housing
- Signal delay caused by ionospheric electrons
- The angular misalignment between the EDM and prism
Correct answer: Changes in the speed of light through air due to temperature, pressure, and humidity
EDM instruments assume a standard atmosphere; actual temperature, pressure, and humidity alter the speed of light and must be corrected.
LSIT Measurement Technology 4
In GPS surveying, 'PDOP' stands for Position Dilution of Precision.
A PDOP of 2 versus a PDOP of 6 means: