Stereoscopic parallax sensitivity – independence from acquisition settings For a given difference in elevation between two ground points, the measured difference in stereoscopic parallax on overlapping aerial photos is independent of which acquisition choice?

Introduction / Context:
In aerial triangulation and contouring from stereo pairs, the difference in parallax between two points (dp) is used to compute the difference in height (dh). It is important to understand which factors govern dp and which do not, because this informs flight planning and the interpretation of imagery products of different print sizes and overlaps.

Given Data / Assumptions:

• Stereo pair with baseline B, focal length f, and flying height H.
• Parallax–height relation in the usual form p ≈ fB/(H - h) for near-vertical photos.
• Same negatives but prints may be enlarged/reduced; overlap percentage can vary as a planning parameter.

Concept / Approach:

The geometric parallax on the negative is governed by f, B, and H. Overlap percentage is a planning issue that affects how much common area two photos share, but it does not change the parallax magnitude at a given point—provided the point lies within the common overlap. Print/enlargement size uniformly scales parallax measured on paper; the measured dp in millimetres will change with enlargement, but the underlying geometric dp on the negative (and hence dp converted to ground units) is unaffected. Therefore, among the listed choices, percentage of overlap is the factor that does not influence parallax values for points inside the overlap.

Step-by-Step Solution:

Verification / Alternative check:

Two flights with different endlaps (say 55% vs 65%) over the same terrain yield the same parallax for a given point if the point appears in both photos; only the available shared region changes.

Why Other Options Are Wrong:

• Focal length influences image scale and hence parallax directly.
• Overall print size alters the measured parallax in millimetres (though not the normalized geometric value).
• “All of the above” cannot be correct because focal length is not independent.

Common Pitfalls:

Confusing image measurement units (mm on print) with geometric invariants; assuming that higher overlap somehow produces larger parallax—overlap only improves redundancy and coverage.

Final Answer:

Percentage of overlap along the flight