Question:
The point, where the perpendicular, projected through the centre of the lens intersects the photo image is known as
The point, where the perpendicular, projected through the centre of the lens intersects the photo image is known as
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Several special points are defined on an aerial photograph based on different reference lines passing through the lens centre (perspective centre).
Updated On: Jun 16, 2026
- Plumb point
- Isocentre
- Nadir
- Principal point
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The Correct Option is D
Solution and Explanation
Concept:
Several special points are defined on an aerial photograph based on different reference lines passing through the lens centre (perspective centre).
Step 1:
The plumb point (nadir point) is where the vertical (plumb) line through the lens meets the photo, and the isocentre lies on the bisector of the angle between the vertical and the optical axis. These are defined by gravity or the bisector, not by the perpendicular from the lens to the photo plane.
Step 2:
The principal point is the foot of the perpendicular dropped from the centre of the lens onto the photograph, that is, where the optical axis intersects the photo image. This matches the given description exactly.
Answer: Option (4) — Principal point.
Several special points are defined on an aerial photograph based on different reference lines passing through the lens centre (perspective centre).
Step 1:
The plumb point (nadir point) is where the vertical (plumb) line through the lens meets the photo, and the isocentre lies on the bisector of the angle between the vertical and the optical axis. These are defined by gravity or the bisector, not by the perpendicular from the lens to the photo plane.
Step 2:
The principal point is the foot of the perpendicular dropped from the centre of the lens onto the photograph, that is, where the optical axis intersects the photo image. This matches the given description exactly.
Answer: Option (4) — Principal point.
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