[PyMOL] RE: Stereo parameters, again

[Warren L. D. <wa...@de...>]

> I still do not understand your stereo parameters: the 
> stereo_angle should 
> define the rotation (around the y-axis) between the pictures 
> for the left and 
> right eye, whereas the stereo_shift should define whether the 
> origin or 
> midpoint of the picture is within the plane of the screen or 
> in front of or 
> behind it. However, changing the settings of these parameters lead to 
> completely unexpected results: setting the stereo_shift to 
> "0" and the 
> stereo_angle to "3.0" results in a mono picture with no 
> separation at all, 
> whereas setting the stereo_shift to "3.0" and the 
> stereo_angle to "0" leads 
> also to a mono picture shifted to the back. So, could you 
> please check this 
> and maybe explain it again to me?

	After looking back at the code, I realize that these parameters
are perhaps misnamed.  These are not the rotations of the objective, but
rather parameters input into the stereo equations.

stereo_shift is the separation between the two cameras observing the
image, expressed as a % of the distance from the objective.  

stereo_angle is a scaling factor applied to the natural angular
difference which would occur between two eyes at that distance, both
looking at the objective.  

Generally speaking stereo_shift is the main depth control parameter, and
stereo_angle should remain close to 2 in order to generate "correct"
stereo geometry.  However, adjusting stereo_angle can reduce ghosting
and change the apparent Z location of the objective.

Detting stereo_shift to zero makes you a Cyclops (you're basically
telling PyMOL that your eyes are superimposed).

The defaults are:

PyMOL>get stereo_shift,
 get: stereo_shift = 2.00000
PyMOL>get stereo_angle,
 get: stereo_angle = 2.10000

which are tuned to minimize CrystalEyes "ghosting" in the foreground.

The actual translation(+/-) and rotation(+/-) of the camera at
"distance" are:

translation = distance * (stereo_shift/100)

rotation = (stereo_angle/2) * (arctan(stereo_shift/100))
(default = +/- 1.2 deg)

If you want a stronger stereo effect, set stereo_shift to 3, 4, or 5
(resulting in rotations of 1.8, 2.4, and 3.0 degrees, respectively).

Cheers,
Warren