Certified Photogrammetrist Aerial Triangulation & Bundle Adjustment 2 — Questions and Answers
Question 1: What is the collinearity condition in photogrammetry?
- The object point, perspective center, and image point all lie on a straight line (Correct answer)
- Three ground control points must form a right triangle
- Parallel flight lines must be equidistant
- All tie points must be visible in at least three photos
Correct answer: The object point, perspective center, and image point all lie on a straight line
The collinearity condition states that the object point, the camera's perspective center, and the corresponding image point are collinear—forming the mathematical basis for photogrammetric equations.
Question 2: In AT processing, what is a 'pass point'?
- A point measured in consecutive photos along a flight strip to pass geometry forward (Correct answer)
- A control point verified by the client
- The nadir point directly below the aircraft
- A point where two flight lines cross
Correct answer: A point measured in consecutive photos along a flight strip to pass geometry forward
A pass point is measured in consecutive overlapping photographs along a strip to propagate (pass) the geometry from one model to the next.
Question 3: What is the effect of using too few ground control points in a large photo block?
- Shorter processing time with no accuracy impact
- Systematic deformations and poor absolute accuracy of the final product (Correct answer)
- Increased pixel resolution in the output orthophoto
- Reduced number of tie points required
Correct answer: Systematic deformations and poor absolute accuracy of the final product
Insufficient ground control allows systematic block deformations to go uncorrected, degrading the absolute accuracy of the final mapping products.
Question 4: Which accuracy metric is used to evaluate ground control point residuals after bundle adjustment?
- RMSE (Root Mean Square Error) (Correct answer)
- PDOP (Position Dilution of Precision)
- MTF (Modulation Transfer Function)
- GSD (Ground Sample Distance)
Correct answer: RMSE (Root Mean Square Error)
RMSE is the standard metric for evaluating GCP residuals after bundle adjustment, summarizing the overall positional accuracy of the solution.
Question 5: What is a 'degenerate network' in aerial triangulation?
- A network where all control points are collinear or poorly distributed, making the solution unstable (Correct answer)
- A photo block with 100% forward overlap
- A network solved without any tie points
- A block processed without GPS data
Correct answer: A network where all control points are collinear or poorly distributed, making the solution unstable
A degenerate network occurs when control points are poorly distributed (e.g., all collinear), creating rank-deficient normal equations and an unstable or non-unique solution.
Question 6: Airborne GPS/IMU data integrated into bundle adjustment primarily improves which aspect?
- Image radiometric quality
- Reduction in the number of required ground control points (Correct answer)
- Tie point matching speed
- Film flatness during exposure
Correct answer: Reduction in the number of required ground control points
Integrating airborne GPS/IMU (direct georeferencing) data into bundle adjustment drastically reduces the number of ground control points needed while maintaining accuracy.
Certified Photogrammetrist Aerial Triangulation & Bundle Adjustment 2
What is the collinearity condition in photogrammetry?