Surveying
The point where a vertical line through the optical centre of the camera lens intersects the ground, is known as

Perspective centre
Ground principal point
Ground plumb point
Iso-centre

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Surveying
In the prismatic compass

the magnetic needle moves with the box
the graduated circle is fixed to the box and the magnetic needle always remains in the N-S direction
the magnetic needle and graduated circle do not move with the box
the line of the sight does not move with the box

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