Dimensional
Analysis through Perspective, by James R. Williamson &
Michael H. Brill
ASPRS, 1990
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Two of the object's principal axes are parallel to the image
plane.
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Verticals of an object remain vertical in the image.
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Horizontals of an object remain horizontal in the image.
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Parallel lines in depth, converge to a vanishing point
VP which is also the Principal Point
(PP). This is due to the fact that the principal ray and
vanishing lines are parallel.
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The image plane and any object-space plane, i.e., at any depth or range, are
parallel. Thus, for any such object-space plane the scale is
constant in that plane: different objects lying in a given plane will
have same scale.
A. Standard Parameters
Two angles are fixed: azimuth and tilt.
To be able to reconstruct the camera parameters, there must be enough
visual cues to create a grid of known width and height, i.e., this is
equivalent to finding the correct spacing for the ground plane grid in
TIP.
For computations ... look here
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One of the object's principal axes (usually the vertical)
is parallel to the image plane.
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The other two sets of parallels (to the 2 other principal axes) of the
object converge to 2 major vanishing points VPX and VPY.
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The line through VPX and VPY defines the True Horizon Line
(THL).
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The Principal
Point (PP) is at the intersection point of the THL and
the line perpendicular to the THL containing the CS.
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The Camera Station
(CS) is on the circle having as its diameter the
line segment on the THL joining VPX to VPY. It is located on the perpendicular
to the THL drawn from the PP.
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Using VPX, VPY, and PP, the focal length of the camera can
be determined.
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With all the above camera parameters, as well as one additional input
(e.g. a known length or angle in the image) exact metric
information can be inferred about the objects.
A. Standard Parameters
One angle is fixed: tilt.
Azimuth describes the rotation of the vertical plane of the object away
from the orthographic vertical plane - a rotation about the Z axis
(object-space).
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None of the object's principal axes are parallel to the image plane.
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Parallel lines converge to tree major vanishing points VPX, VPY and
VPZ.
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Using the three vanishing points, the Principal Point (PP) can be
determined.
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Using any two vanishing points and PP, the focal length of the camera
can be determined.
-
With all the above camera parameters, as well as one additional input
(e.g. a known length or angle in the image) exact metric information
can be inferred about the objects.
A. Standard Parameters
The three angles may vary.
If the tilt is greater than +90 degrees, than the camera is pointing
upward (worm's eye viewpoint), otherwise ti camera point downward
(bird's eye viewpoint).