[vtkusers] Speed of zoom

James C. Robinson j.robinson at kepler-systems.com
Wed Apr 21 16:44:34 EDT 2004


Lisa,

Many thanks for the tip. The problem in using the view angle is exactly that
to which you alluded.... the position of the viewer (camera) in the space. I
assume that the implication is that if the camera is turned left or right,
the viewer would not, in fact, have moved from his/her position (and thus,
if moving through a scene, the user, in changing the camera viewing angle,
would have had the impression of moving along a line further into the scene,
but in fact would effectively have used a zoom analogous to using a real
camera zoom).

Is it not possible to either (a) invoke a method that ensures that the focal
point is always suitable far away from the camera or (b) set the focal point
to a position that is far enough away from the camera that it is never an
issue (I assume that this is what happens when I "approach" my object from
an angle such that the zoom slowdown is never an issue)?

Regards,

Jim

______________________

James C. Robinson, PhD,
Chartered Engineer,
Kepler Simulation Systems Ltd.,
42 Rivergrove,
Glanmire, Co. Cork,
Eire

Tel:         +353-21-4822028
Tel:         +353-87-2393010
Fax:        +353-21-4822028
E-mail:     j.robinson at kepler-systems.com
______________________

-----Original Message-----
From: Lisa Avila [mailto:lisa.avila at kitware.com]
Sent: 21 April 2004 17:54
To: j.robinson at kepler-systems.com; Vtk Users
Subject: Re: [vtkusers] Speed of zoom


When you "zoom" by moving the camera closer / farther from the focal point
(called "dolly") this will happen. The movement is a fraction of the
current distance from the camera position to the focal point - hence when
you get really close to the focal point you are only moving very small
distances.

An alternate way to "zoom" is to change the view angle - here you can get a
smoother effect, but keep in mind that your camera doesn't actually move
(which can be confusing when a user tries to navigate through the scene
using your "zoom" functionality)

Lisa


At 11:25 AM 4/21/2004, James C. Robinson wrote:
>Dear All,
>
>I may have posted this query already (as it is an ongoing wish list
member).
>I refer to the use of the mouse for zooming, panning etc. in a window.
>Sometimes, for reasons I have not quite figured out (although I suspect it
>has something to do with either the position of the camera focal point or
>the object origin) the zoom capability (or pan) slows down such that a
large
>movement in the mouse cursor position results in a very small change (zoom
>or pan) on the view. That is, I might be zoomed in to a certain distance
>from an object (or detail of an object) and, depending on "how" I zoomed
in,
>the subsequent zoom power can vary from strong to very slight.
>
>Has anybody (a) any idea what I am talking about and (b) any suggestions as
>to what is going on and what one can do to control this apparently (though
I
>am sure it is not) arbitrary behaviour. NB: I cannot find any detailed
>reference to the interactor type control involved here in the doc (it
refers
>only to "dolly" etc. when explaining zooming).
>
>Many thanks,
>
>Jim
>
>______________________
>
>James C. Robinson, PhD,
>Chartered Engineer,
>Kepler Simulation Systems Ltd.,
>42 Rivergrove,
>Glanmire, Co. Cork,
>Eire
>
>Tel:         +353-21-4822028
>Tel:         +353-87-2393010
>Fax:        +353-21-4822028
>E-mail:     j.robinson at kepler-systems.com
>______________________
>
>
>
>_______________________________________________
>This is the private VTK discussion list.
>Please keep messages on-topic. Check the FAQ at:
><http://public.kitware.com/cgi-bin/vtkfaq>
>Follow this link to subscribe/unsubscribe:
>http://www.vtk.org/mailman/listinfo/vtkusers






More information about the vtkusers mailing list