RPLS Quality Control Procedures 3 โ Questions and Answers
Question 1: Which statistical measure describes the spread of repeated observations around their mean value?
- Mean absolute error
- Standard deviation (Correct answer)
- Probable error
- Root mean square residual
Correct answer: Standard deviation
Standard deviation (ฯ) quantifies the dispersion of individual observations about the mean and is the fundamental measure of precision.
Question 2: During a control survey, the surveyor computes an angular misclosure of 42 seconds for a 7-sided polygon traverse. What is the per-angle correction?
- +6 seconds per angle
- โ6 seconds per angle (Correct answer)
- +42 seconds to one angle
- โ3 seconds per angle
Correct answer: โ6 seconds per angle
The misclosure of 42 seconds is distributed equally by subtracting 6 seconds (42 รท 7) from each measured interior angle.
Question 3: A 'peg test' on a level instrument is designed to detect and correct which condition?
- Horizontal collimation error
- Vertical circle index error
- The line of sight not being truly horizontal (collimation error) (Correct answer)
- Compensator malfunction in digital levels
Correct answer: The line of sight not being truly horizontal (collimation error)
The peg test determines whether the instrument's line of sight is truly horizontal when the bubble is centered, detecting and correcting the i-angle (collimation error).
Question 4: In a GPS survey, what does a PDOP (Position Dilution of Precision) value greater than 6 indicate?
- Excellent satellite geometry for high accuracy
- Poor satellite geometry that may degrade positional accuracy (Correct answer)
- The receiver has lost lock on all satellites
- The ionospheric correction model is invalid
Correct answer: Poor satellite geometry that may degrade positional accuracy
PDOP > 6 indicates poor satellite geometry where satellites are clustered close together, weakening the three-dimensional position solution.
Question 5: What is the primary QC benefit of computing the 'compass rule' (Bowditch) adjustment vs. simply accepting raw traverse coordinates?
- It eliminates all measurement errors from the traverse
- It distributes linear misclosure proportionally to leg length, producing consistent adjusted coordinates (Correct answer)
- It corrects angular errors before linear errors
- It automatically weights measurements by instrument precision
Correct answer: It distributes linear misclosure proportionally to leg length, producing consistent adjusted coordinates
The compass rule adjusts latitudes and departures in proportion to each leg's length, distributing linear misclosure to produce geometrically consistent final coordinates.
Question 6: A surveyor notices that benchmark elevations derived from a long level circuit differ by 0.08 ft from published NGS values. The best first QC step is to:
- Accept the difference since it is within allowable tolerance
- Re-run the level circuit in the opposite direction to isolate the error (Correct answer)
- File a report with NGS to update the published benchmark
- Average the two values and use the result
Correct answer: Re-run the level circuit in the opposite direction to isolate the error
Running the circuit in reverse provides an independent check that isolates whether the discrepancy is in the surveyor's work or in the published benchmark.
Question 7: Which document type formally defines the accuracy standards that a land survey must meet before being delivered to the client?
- Field notes
- The deed description
- The project specifications or scope of work (Correct answer)
- The plat certificate
Correct answer: The project specifications or scope of work
Project specifications or the scope of work define the required accuracy class, methods, and deliverable standards that QC must verify before project delivery.
RPLS Quality Control Procedures 3
Which statistical measure describes the spread of repeated observations around their mean value?