Homologous points – identify the correct description Which statement correctly describes homologous points in a stereoscopic pair of aerial photographs?

Difficulty: Easy

Correct Answer: They are corresponding images of the same ground point on the two overlapping photographs

Explanation:


Introduction / Context:
Correctly identifying homologous points is the cornerstone of stereo compilation, height determination, and aerotriangulation. This question checks the conceptual definition applied in practical stereoscopic analysis.



Given Data / Assumptions:

  • Two overlapping aerial photos form a stereo pair.
  • Each ground point within overlap appears twice, once in each photo.
  • Parallax arises due to different camera positions.



Concept / Approach:
Homologous points are the corresponding image points on the left and right photographs that represent the same physical feature on the ground. Their horizontal displacement along the flight direction (parallax) is exploited to recover elevation through photogrammetric formulas and model intersections.



Step-by-Step Solution:
Identify the nature of correspondence: one real-world feature → two photo images.Reject single-photo special points (principal, nadir) and lens nodal points.Select (c) as the correct descriptive statement.



Verification / Alternative check:
Stereoplotters and modern dense-matching algorithms automatically search for homologous points to reconstruct 3D point clouds, validating the definition.



Why Other Options Are Wrong:

  • (a) Opposite corners of a single photo are unrelated to stereo correspondence.
  • (b) Nodal points are optical-system constructs, not image correspondences.
  • (d) Plumb points (nadir) are unique points per photo; they are not “correspondences” of arbitrary terrain features.



Common Pitfalls:
Assuming a ground-photo pair constitutes “homologous” points; the term applies to two photos, not ground vs. photo.



Final Answer:
They are corresponding images of the same ground point on the two overlapping photographs

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