# [Chimera-users] camera horizontal field of view

Tom Goddard goddard at sonic.net
Mon Jul 8 17:06:32 PDT 2013

```Hi Matt,

I agree that limiting the field of view to 179 degrees in the Chimera Camera dialog is a bit wacky.  But the angle does have to be less than (and not equal to) 180 degrees because it is the width of the rectangular graphics window as seen from the position of the camera.  It is mathematically impossible for that to be 180 degrees or more.  The human eye is not a flat rectangular screen perspective projection and it can possibly exceed 180 degrees field of view.

If the virtual camera used by Chimera is positioned at your eye you could compute the field of view using the distance of your eye to the screen and the width of the Chimera graphics window.  For example if I view my screen from 50 centimeters away and my graphics window is 20 centimeters wide, then some trigonometry shows the width of the graphics window as viewed from my eye is 22.6 degrees.  Chimera has in the Camera tab of the Side View dialog parameters called distance to screen and screen width.  Here's the trigonometry formula relating the field of view angle to these.

field of view = 2 * atan(0.5*d/w)

where d = distance to screen and w = graphics window width.  When programming atan() will return radians, and to convert to degrees you'd want to multiply by 180/pi.

After saying all that, I'd say that using the physically correct field of view is not necessary.  You can get as good and sometimes better presentation of data using wider or narrower field of view and the human eye is not confused by this.  With stereo projection it is probably more important to worry about physically realistic viewing geometry to avoid eye strain.

Tom

On Jul 8, 2013, at 3:14 PM, "Dougherty, Matthew T" wrote:

> The camera settings allow for a horizontal field of view of 1-179 degrees.
>
> Wikipedia states that human horizontal field of view is ~180 degree.
> using 179 is not anything I normally recognize, looks like star trek enterprise going to warp.
> In cinematography books, lenses are sometimes referenced at around 20 degrees.
>
> For chimera I have found 10-30 gives nominal viewing on LCD.
> Setting it 1 is effectively orthographic.
> For DTI in a dome projection (as opposed to dome camera), I frequently will use 80-110, unless I am looking for a orthographic look, then lower values.
>
> For the mono & DTI cameras on a flat display, what are the values or the process to determine the values, for the most accurate mapping to normal human vision?
>
>
>
> Matthew Dougherty
> National Center for Macromolecular Imaging
> Baylor College of Medicine
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```