Sightline
This computes the focal length a surveillance camera needs from its mounting
height, its distance to the scene and the width of scene it has to cover, and then
draws what that lens would see. Both halves need JavaScript.
The arithmetic is one line and is worth having regardless. A lens of focal
length f on a sensor w millimetres wide covers a scene
W metres across at a range of R metres when
f = w · R / W. The range is the straight line from the lens to the
subject — the square root of the ground distance squared plus the height of the
lens above the subject squared — and not the distance along the ground, which is
the step most calculators skip.
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