[Chimera-users] Stereo angle value

Greg Couch gregc at cgl.ucsf.edu
Tue May 2 13:17:06 PDT 2006

On Wed, 26 Apr 2006, Prof. Fabrizio Briganti wrote:

> I have not been able to find any reference to the value for the angle
> difference between Right and Left views in Stereo Images made with Chimera.
> Can you help me find it?
> Is there any way to change such angle value?

To control the viewing angle and stereo separation, chimera uses 3 
distances which must be given in the same units (e.g., cm, mm, inches). 
They are the distance between the viewer's eye, the distance from the eyes 
to the screen, and the width of the screen.  Currently, there is no GUI to 
change those distances, but you can change them via a Python script, or 
interactively by typing in the the IDLE dialog window (Tools / General 
Controls / IDLE).

The distances are:


And they default to 2.0, 30.0, and 13.0, respectively (inches).  Your 
brain is amazingly good at compenstating for inaccurate values, so the 
only distance that you should modify is the viewDistance.  Adjusting the 
view distance will change how much depth is perceived in the image -- from 
either too much or too little to "just right".  Small viewing distances 
also give a wide-angle effect.

So typing into the IDLE window:

 	chimera.viewer.camera.viewDistance = 15

Will move the eye halfway to the screen and increase the angle.  Smaller 
values give more depth.

Another important part of stereo perception is the amount of positive and 
negative parallax -- i.e., how much of the molecule is behind or in front 
of the screen.  By default, chimera puts the center of the molcule in the 
plane of the screen for half positive and half negative parallax.  The 
smaller the view distance, the more likely that is too much negative 
parallax to comfortably view the image, so translate the molecule away 
from you to increase the positive parallax and reduce the negative 

 	Hope this helps,

 	Greg Couch
 	UCSF Computer Graphics Lab

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