Converting XSI_FOV 2 real FOV 2004-05-11 - By Sam Cuttriss
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if i remember correctly matt lind posted this a while back...
"Here are two artciles from the Knowledge base:
By design, the SOFTIMAGE 3D camera custom angle is the vertical angle and
not the standard lens angle (which is the horizontal angle). When you use
the SOFTIMAGE 3D camera data (usually for tracking purposes), you must first
convert the vertical angle to the horizontal angle and then use the
resulting data. If you use the camera data before converting it, with the
assumption that the angle is on the horizontal, the resulting scene images
will appear distorted. To avoid this problem, use the following conversion
formula:
* If you have the vertical angle and the aspect ratio, to find the
horizontal angle, apply the two known values to the following formula:
Horizontal = 2 * arctan (aspect * tan(Vertical / 2)
-or-
* If you require the vertical angle, and know the horizontal value and
the aspect ratio, apply the two known values to the following formula:
Vertical = 2 * arctan (tan(Horizontal / 2) / aspect)
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The SOFTIMAGE 3D camera's field of view (FOV) is measured with the vertical
lens angle, not the standard horizontal lens angle. Therefore, if you need
to use the SI3D camera data for other purposes, you must first convert the
vertical lens angle to the horizontal lens angle and then use the data.
MORE INFORMATION
To get the proper FOV for a particular shot you must know: lens focal length
(55mm, 80mm, etc.), media (35mm film, or 16mm film), and type of camera
(vistavision, 4-perf, still, etc - because one type of film is used
differently in different cameras).
Use the following formula to calculate the horizontal and vertical angles
when you know the focal length, and either the width, or the height of the
exposed surface of the film:
Horizontal angle = 2 * arctan (width/(2 * f))
Vertical angle = 2 * arctan (height/(2 * f))
"
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