[vtkusers] Distance from eye to viewplane

[Vinicius Rogério Araujo Silva]

Actually, R is not the radius of the cone's base. Rather, the radius is
calculated based on the values of R and H.
One more thing. A question about your example:

Renderer->SetDisplayPoint(x, y, z);
Renderer->DisplayToWorld();
double p[3];
Renderer->GetWorldPoint(p);

Let me see if I understood it correctly.
If I set Z to a value that is equal to the Near Clipping Plane's distance,
then the output will be a point that lies on the near clipping plane?

Thank you for your answers!

Em 17 de dezembro de 2010 20:30, David Gobbi <david.gobbi at gmail.com>escreveu:

> 2010/12/17 Vinicius Rogério Araujo Silva <vinicius.ras at gmail.com>
>
>> Well, these conversion functions will help me a lot.
>> But I got a little confused about the viewplane now..
>>
>> Can I consider the near clipping plane as the viewplane?
>> Are they the same thing?
>>
>
> As far as I know, any plane that is parallel to the near or
> far clipping planes can be considered a "view plane".  But since you need to
> know the distance, you have to choose one specific plane: usually the near
> plane, the far plane, or the focal plane.
>
> I'll try to explain my problem a bit further.
>> I'm trying to implement a selection algorithm which involves a cone. The
>> user should be able to select points that lie inside of that "virtual cone".
>> Because of my application's requirements, the user should be able to
>> provide two things to the application: a radius R and an height H.
>> Then the application should then be able to calculate the cone in the
>> following way: the height of the cone will be given by H, and the radius
>> will be calculated as a value proportional to H, in such a way that if H
>> equals the distance from the camera to the viewplane, the radius of the
>> cone's base will be R.
>>
>
> You lost me here.  First you say that the user chooses R and H, and then
> you say that R will be calculated.
>
>
>> That is why it is so important to me to find the distance from the camera
>> to the viewplane.
>> Also, I've tried using the near clipping plane as the "viewplane" of my
>> problem, but unfortunately it did not produce the results I've expected.
>>
>
> The viewplane that you choose should be the plane at the base of your cone.
>  I'm guessing that your cone has its tip at the camera position, and has its
> base either at the far clipping plane or at some position in between the
> near and far clipping plane.  Wherever its base is, I'm guessing that you
> should use that position as your view plane.  So the distance to the view
> plane is H, i.e. whatever you choose as the height of the cone.  I might be
> misunderstanding, though.
>
>   David
>
>
>
>>
>> Em 17 de dezembro de 2010 02:02, David Gobbi <david.gobbi at gmail.com>escreveu:
>>
>> 2010/12/16 Vinicius Rogério Araujo Silva <vinicius.ras at gmail.com>:
>>> > Hi all,
>>> > I'm new to VTK and after spending some time searching, I've decided to
>>> join
>>> > the mailing list to see if you guys can help solving my questions.
>>> > It seems pretty simple, yet I just couldn't find a way to solve it.
>>> > Question is:
>>> > Is there any way to retrieve the distance between the eye of projection
>>> > ("camera") and the view plane?
>>> > Or is there any way I can retrieve the plane equation for the view
>>> plane?
>>> > Any help is really apreciated. Thank you.
>>>
>>> Camera->GetClippingRange() is probably what you want, it will return the
>>> distance from the camera to the near and the far clipping planes.  You
>>> can
>>> use Camera->GetViewPlaneNormal() to get the normal.
>>>
>>> The renderer also has methods for doing coordinate conversion between
>>> display coordinates (i.e. pixels at the view plane) and world coordinates
>>> (i.e. 3D coordinates in the scene):
>>>
>>> Renderer->SetDisplayPoint(x, y, z);  // use z = 0 for view plane
>>> Renderer->DisplayToWorld();
>>> double p[3];
>>> Renderer->GetWorldPoint(p);
>>>
>>> So you can, for instance, give the display coords for the four corners of
>>> your window, and this will provide the 3D coords corresponding to the
>>> corners of the view plane.  Display coords start from (0,0) in the lower
>>> left corner of the window.
>>>
>>>   David
>>>
>>
>>
>
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