[vtk-developers] Strange behavoir in vtkCamera

[Lisa Avila]

Hello Silvano,

Changing vtkCamera::ComputePerspectiveTransform would change more than just 
the reset camera functionality - it would change the notion of how the view 
angle is measured. Of course, looking at the code I now see that there is a 
UseHorizontalViewAngle flag (default 0) that can be used to consider the 
view angle in the x rather than the y direction. You could then write your 
own reset functionality that switched this variable based on whether the 
width or the height of the window was greater.

One other note - it looks like Chris Volpe made the change to add the 
horizontal option - but it does not seem to be propagated to the parallel 
case (just in perspective). I suspect this is a bug and I will correct it. 
I am suspicious of this change - there are places outside of vtkCamera that 
assume that the field of view defines the angle in Y and unless all of 
these were changed as well then it is likely that using the horizontal flag 
will result in bad images.

Lisa



At 12:48 PM 3/25/2003, Silvano Imboden wrote:
>Lisa Avila wrote:
>
>>Hello Silvano,
>>This is actually the expected behavior of vtkCamera - the field of view 
>>is defined as view frustum angle in the Y direction and is therefore 
>>solely dependent on the height of the window.
>>Lisa
>
>First I'll thank you for your real-time-feedback.
>
>I think that it is a common aspectation
>that ResetCamera bring everything in view
>whatever is the aspect-ratio
>of the RenderWindow.
>So in my modest opinion this behavoir is wrong.
>
>Anyway
>
>- Do you think that change implementation of
>   vtkCamera::ComputePerspectiveTransform
>   like I show in my previous mail
>   may have some bad side-effect ?
>
>- can you make vtkCamera::ComputePerspectiveTransform
>   virtual ?
>
>Many thanks -- Silvano
>======================
>s.imboden at cineca.it
>======================
>
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