Stereophotography — “want of correspondence” and its dependencies In overlapping aerial photographs, the want of correspondence (difficulty in matching homologous image points) has which characteristic?

Introduction / Context:
“Want of correspondence” describes the inability to locate matching points on a stereo pair due to image distortions or scale differences. Minimizing it is essential for accurate stereo-compilation and parallax measurement.

Given Data / Assumptions:

• Two overlapping photos intended for stereoscopic viewing.
• Potential causes include camera tilt, height differences, lens distortions, time gap changes, and relief.

Concept / Approach:

Tilt introduces perspective differences and non-uniform scale across the photos, making homologous points harder to match. Differences in flying height between exposures also change scale, increasing want of correspondence. Therefore, want of correspondence is indeed a function of tilt (among other factors) and must be minimized by good flight planning and camera stabilization.

Step-by-Step Solution:

Verification / Alternative check:

Photogrammetric specifications set limits on average and differential tilt to control this problem, and require nominally constant flying height to maintain scale consistency.

Why Other Options Are Wrong:

• (a) It is detrimental, not desirable.
• (c) False: flying height changes do affect correspondence via scale change.
• (d) No special minimum at 3°; lower tilt is generally better.
• (e) Focal length alone does not govern the effect.

Common Pitfalls:

• Assuming large overlaps alone solve correspondence; attitude and height consistency also matter.

Final Answer:

It is a function of tilt.