Photogrammetry and stereoscopy — standard value of human eye base In stereoscopic plotting and visual perception calculations, what average interpupillary distance (eye base) is typically assumed for a normal adult observer?

Introduction / Context:
In air-photo interpretation and stereoscopic vision, the eye base (interpupillary distance) is used when relating stereo parallax to perceived depth. A standard average value allows consistent calculations for stereoscopes and ergonomic setup of plotting instruments.

Given Data / Assumptions:

• Question asks for the typical average eye base used in practice.
• Normal adult population; specialized clinical variations are ignored.
• Conventional photogrammetric assumptions are applied.

Concept / Approach:
The interpupillary distance in adults commonly ranges from roughly 58 mm to 70+ mm. For design and calculation purposes, most photogrammetry texts take a representative mean value near the center of this range. The widely adopted standard is approximately 62 mm, which is used to model comfortable stereo viewing geometry and to scale stereo parallax–depth relations in simple calculations.

Step-by-Step Solution:

Verification / Alternative check:
Manufacturers of stereoscopes and training manuals often cite 62–65 mm as practical settings, with 62 mm being the canonical default for calculations.

Why Other Options Are Wrong:

• 58 mm, 60 mm, 64 mm, 72 mm are plausible individual IPDs but are not the typical standard assumption used in stereoscopic calculation references.

Common Pitfalls:
Confusing a device's adjustable eyepiece spacing with the standard value used for theoretical calculations; using an extreme IPD that does not represent the average observer.

Final Answer:
62 mm