[vtkusers] Parallel Projection to Perspective Mode calculation

[David Gobbi]

Basic trigonometry.  Imagine a right triangle with its pointy end at the
camera and its "foot" at the focal point.  If the angle at the foot is
"phi", then the height at the foot is d*tan(phi) where "d" is the camera
distance.

Perspective view angle is 2*phi.  Parallel height is 2*d*tan(phi).

 - David


On Wed, Sep 6, 2017 at 12:16 PM, Doug Hoppes <dhoppes at mbfbioscience.com>
wrote:

> Hey all,
>
>
>
>                 What is the calculation between parallel projection and
> perspective mode?  I have a situation where the user is in Parallel
> Projection Mode and then zooms in on the object in my scene. When he
> switches to Perspective Mode, he would like the scene to look the same
> (i.e. move the camera to that location).
>
>
>
> Dougie
>
>
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