Aerial photo geometry: identify the correct statements about photographic tilt, principal line direction, and the principal plane on a tilted photograph.

Introduction / Context:
Even small departures from strict verticality in aerial photography introduce tilt, which affects scale, relief displacement patterns, and orientation procedures. Understanding the geometric elements—tilt angle, principal line, principal plane—is essential for accurate photogrammetric corrections.

Given Data / Assumptions:

• Tilted photograph with perspective centre (camera station), principal point, and plumb point identifiable.
• Perspective axis is the line through the lens perpendicular to the image plane (at exposure).

Concept / Approach:

• Tilt: angle between the negative plane and a horizontal plane that contains the perspective axis.
• Principal line: intersection of the photograph plane with the principal plane; it gives the direction of maximum tilt.
• Principal plane: truly vertical plane through the perspective centre that contains the principal point and the plumb point; it defines the geometry of tilt.

Step-by-Step Solution:
Identify definitions: (a) tilt definition matches standard photogrammetric usage.(b) Principal line indicates maximum tilt direction on the photo.(c) Principal plane includes perspective centre, principal point, and plumb point and is vertical.All three statements are correct.

Verification / Alternative check:
Photogrammetry texts depict these relationships consistently; tilt corrections rely on these definitions.

Why Other Options Are Wrong:
Any subset (e.g., only (a) and (c)) omits a correct statement; hence “All the above” is required.

Common Pitfalls:
Confusing the principal point with the nadir point; misidentifying the plumb point location.

Final Answer:
All the above