In terrestrial photogrammetry, the base–height ratio is a critical parameter. For a given camera focal length and object distance, a larger base–height ratio improves
- Athe scale of the photograph
- Bthe overlap between successive photographs
- Cthe resolution of the image
- Dthe accuracy of depth measurementCorrect
Solution
Concept
Base-height ratio effect on depth measurement accuracy
Formula
σZ = (Z2 / (B × f)) × σp
Step-by-step solution
1. The error in depth or distance Z in photogrammetry is inversely proportional to the base length B (σZ proportional to 1/B). 2. Increasing the base-height ratio (B/H or B/Z) increases the intersection angle of conjugate camera rays. 3. This greater convergence increases parallax difference per unit depth, substantially improving depth measurement accuracy. Answer: D
Explanation
In terrestrial photogrammetry, increasing the base-height (or base-to-distance) ratio widens the parallax intersection angle of optical rays intersecting on the object. A wider convergence angle significantly enhances stereoscopic parallax sensitivity, directly improving the precision and accuracy of depth (Z-coordinate) measurement. Therefore, option D is correct.
Why the other options are wrong
A) Photograph scale is governed by focal length and object distance (f/H), not air base. B) Increasing base length reduces the photographic overlap area. C) Image resolution depends on camera sensor optics and distance, not base spacing.
Shortcut
Larger B/H = Wider ray intersection = Higher vertical and depth accuracy.
Common mistake
Thinking larger base-height ratio increases photograph overlap; increasing base actually reduces stereo overlap.
Correct answer: D) the accuracy of depth measurement