[Chimera-users] Zooming and orthographic projection mode

Thomas Goddard goddard at cgl.ucsf.edu
Mon Sep 14 11:24:47 PDT 2009

Hi James,

   I see sometimes zooming in close in orthographic projection is not 
possible while it works fine in perspective in the current daily build. 
      That is a bug and I'll create a bug report.

   Zooming behavior has changed between Chimera 1.3 and 1.4.  Here are 
some details that may help you.  Zooming moves your view closer to a 
point at a certain depth in the center of the screen.  What depth?  In 
Chimera 1.3 the point to zoom in on was a hidden parameter (called 
"center") not shown in the Camera panel.  It was set when you used the 
focus, window, or center commands and when you first opened a model to 
the center of the bounding sphere.  In 1.4 I changed this to zoom in 
towards the center of rotation.  The default location for the center of 
rotation also changed from 1.3 to 1.4.  In 1.3 it was the center of the 
bounding sphere of the displayed models.  In 1.4 if you are zoomed in it 
rotates about the closest visible object in the center of the screen and 
if you are zoomed out it uses the older center of bounding sphere.  By 
"zoomed in" I mean that the bounding sphere of the displayed models is 
at least twice as big as the window width.  The result is that in 1.4 
daily builds you should zoom in on the closest visible object in the 
center of the window.  In 1.3 you would zoom in on a point that may be 
in front of the closest visible object (so you could never get close) or 
  may be behind the closest visible object (so you would collide with 
the object when zooming).  What I've described seems to be working 
correctly for perspective projection (the default projection mode). 
Something seems slightly wrong (but not too far wrong) for orthographic 
projection where you can't get as close as you want.

   Last week I fixed a bug that may be causing your problem.  It was a 
bug where the center of rotation point was not calculated correctly but 
was put in front of the closest visible object in the center.  That 
would prevent zooming in (in both perspective and orthographic 
projection).  It only occurred when multiple models were shown in 
certain spatial arrangements (a model in front had no object in center 
of window, but its center of bounding box was in front of closest 
visible object).  That was fixed September 8.


-------- Original Message --------
Subject: [Chimera-users] Zooming and orthographic projection mode
From: James Conway
To: chimera-users
Date: 9/11/09 12:45 PM

> I am struggling a bit and would be interested in any pointers from the  
> knowledgeable folk here. It seems that I cannot use the mouse to get  
> arbitrarily close to a surface in orthographic mode, but I can in  
> perspective mode. In orthographic mode (Viewing -> Camera ->  
> Projection) if I try to zoom in, the camera instead moves in until the  
> front surface clips, but without much actually zooming. (True for the  
> different "Center of Rotation" methods). In the Viewing -> Side View  
> panel, the width of the field is represented by red lines that I  
> cannot control but which I really want to move close together.
> According to the help for the Viewing -> Camera panel:
>      horizontal field of view (allowed range 1.0-179.0°) - how much
>         perspective is used; does not affect the orthographic
>         projection. The vertical field of view will change along
>         with the horizontal field of view, but their exact
>         relationship depends on the aspect ratio of the graphics
>         window.
> In fact, with the nightly builds of 1.4 this parameter *does* affect  
> the orthographic projection, and does zoom in (or out) without  
> clipping. Is there an updated explanation of how this works, and if it  
> has changed since 1.3 as I seem to find? Am I looking in the wrong  
> place for help on nightly builds?
> Thanks,
> James Conway
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> Chimera-users at cgl.ucsf.edu
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