Photogrammetric parallax — contributors to measured parallax on a photograph The stereoscopic parallax of a point measured on overlapping aerial photographs is influenced by which factors?
Civil Engineering
Advanced Surveying
Difficulty: Easy
Choose an option
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AGround elevation of the point
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BFlying height above datum/ground
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CLength of the air base (or photo base)
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DCamera focal length
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EAll of the above
Answer
Correct Answer: All of the above
Explanation
Introduction / Context:Parallax is the apparent displacement of image points between two overlapping photos and is central to height determination in photogrammetry.
Given Data / Assumptions:
- A standard vertical aerial photography setup with overlap.
- Rigid camera geometry with known focal length.
Concept / Approach:
Parallax p is commonly related by p ≈ (B f)/(H − h), where B is air base, f is focal length, H is flying height above datum, and h is ground elevation. Thus, each listed factor directly influences measured parallax values.
Step-by-Step Solution:
Increase h (higher ground) → denominator decreases → parallax increases.Increase H → denominator increases → parallax decreases.Increase B or f → numerator increases → parallax increases.Verification / Alternative check:
Analytical stereotriangulation models and mapping camera geometry yield the same dependencies.
Why Other Options Are Wrong:
- Each single factor is indeed influential; the comprehensive option is therefore correct.
Common Pitfalls:
- Confusing photo base (on image) with air base (in space); both relate via scale.
Final Answer:
All of the above.