The Forced Perspective calculator computes the angle based on the height of the object and distance to the object.
INSTRUCTIONS: Choose units and enter the following:
Force Perspective (Θ): The calculator returns the angle in degrees. However this can be automatically converted to compatible units via the pull-down menu.
The formula for force perspective is:
`Θ = 2 tan^(-1)(h/(2D))`
where:
Forced perspective is a technique which employs optical illusion to make an object appear farther away, closer, larger or smaller than it actually is. It manipulates human visual perception through the use of scaled objects and the correlation between them and the vantage point of the spectator or camera. It has applications in photography, filmmaking and architecture.
This is the formula for calculation angular size, where θ is the subtended angle, h is the actual size of the object and D is the distance from the lens to the object.
Source: Wikipedia
https://en.wikipedia.org/wiki/Forced_perspective