RPLS Quality Control Procedures 2 — Questions and Answers
Question 1: When performing a closure check on a traverse, what does a closure ratio of 1:5,000 indicate?
- The traverse meets first-order accuracy standards
- For every 5,000 units measured, there is 1 unit of linear error (Correct answer)
- The angular closure error is 5,000 seconds
- The traverse has 5,000 redundant measurements
Correct answer: For every 5,000 units measured, there is 1 unit of linear error
A closure ratio of 1:5,000 means there is one unit of linear misclosure for every 5,000 units of total traverse length.
Question 2: Which QC procedure best detects systematic errors in GPS baseline measurements?
- Increasing the observation session duration
- Comparing independently computed baselines that form closed loops (Correct answer)
- Using a higher-precision receiver
- Collecting data during solar maximum
Correct answer: Comparing independently computed baselines that form closed loops
Closing GPS baselines into loops and computing the loop misclosure is the primary method for detecting systematic errors in GNSS surveys.
Question 3: A surveyor re-measures a distance three times and gets 100.02, 100.03, and 100.01 feet. What is the most probable value?
- 100.01 ft
- 100.02 ft (Correct answer)
- 100.03 ft
- 100.025 ft
Correct answer: 100.02 ft
The arithmetic mean (100.02 + 100.03 + 100.01) / 3 = 100.02 ft is the most probable value for a series of direct measurements.
Question 4: What is the purpose of using a 'check shot' to a known point during a total station survey?
- To calibrate the instrument's EDM
- To verify the instrument setup has not shifted or been disturbed (Correct answer)
- To establish a new control point
- To compute the local magnetic declination
Correct answer: To verify the instrument setup has not shifted or been disturbed
Periodically observing a check shot to a known point confirms that the instrument setup remains undisturbed and the orientation is still valid.
Question 5: In leveling, which check confirms that the sum of backsights minus the sum of foresights equals the change in elevation?
- Page check (Correct answer)
- Double-rodded check
- Reciprocal leveling check
- Three-wire closure check
Correct answer: Page check
A page check verifies arithmetic by confirming that ΣBS − ΣFS = last elevation − first elevation on each page of field notes.
Question 6: A surveyor discovers that a prism pole was not fully extended to 2.000 m during data collection but was set at 1.987 m. This is an example of which error type?
- Random error
- Systematic blunder
- Personal mistake (blunder) (Correct answer)
- Instrumental error
Correct answer: Personal mistake (blunder)
Failing to fully seat a prism pole is a personal mistake or blunder, not a systematic error, because it results from operator carelessness rather than a consistent bias.
Question 7: When should a surveyor perform an independent check of field measurements before leaving a project site?
- Only if the project exceeds one acre in size
- Always, to detect blunders while equipment is still in place (Correct answer)
- Only when the client specifically requests it
- After returning to the office and processing the data
Correct answer: Always, to detect blunders while equipment is still in place
Checking critical measurements before leaving the site allows blunders to be corrected immediately while the setup is intact, saving costly return trips.
RPLS Quality Control Procedures 2
When performing a closure check on a traverse, what does a closure ratio of 1:5,000 indicate?