[vtkusers] Speed of zoom

[James C. Robinson]

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
>______________________
>
>
>
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