Photogrammetric nomenclature — “plate parallel” on the negative In aerial photo geometry, a plate parallel is defined as the line on the plane of the negative that is how oriented relative to the principal line?

Introduction / Context:
Precise terminology in aerial photogrammetry helps practitioners describe geometry on a photograph. Key lines include the principal line (through the principal point and isocentre), the horizon (tilt) line, and named parallels used in setting up instruments and interpreting tilt effects. Misnaming these lines can lead to orientation mistakes and measurement errors.

Given Data / Assumptions:

• We are working on the plane of a photographic negative or its positive print.
• The principal line is known: it passes through the principal point and the isocentre (and also aligns with the plumb point on a tilted photo).
• The term “plate parallel” must be related unambiguously to this principal line.

Concept / Approach:
By common photogrammetric convention, a plate parallel is a line on the photograph that is parallel to the principal line. While the horizon (tilt) line has its own definition (perpendicular to the direction of maximum tilt and related to vanishing points), the plate parallel specifically follows the direction of the principal line, serving as a convenient reference for layout and analysis.

Step-by-Step Solution:

Verification / Alternative check:
Orientation diagrams in standard photogrammetry texts depict plate parallels as auxiliary lines parallel to the principal line to aid in geometric constructions and reductions for tilt.

Why Other Options Are Wrong:

• Perpendicular or angular bisector relations describe other constructions, not the plate parallel.
• “None of these” is incorrect because a simple, direct definition exists.
• Linking it only to the horizon line confuses distinct geometrical entities.

Common Pitfalls:
Confusing principal, horizon, and tilt lines; assuming definitions change between negative and print (they do not, aside from orientation reversals).

Final Answer:
Parallel to the principal line