[vtkusers] How to preserve objects size when moving camera

[Andrey Ivanov]

I forgot to mention that I am already working with orthogonal projection.
The problem is not with preserving shapes and avoiding perspective
deformations. I would like to fix screen size of objects, so when I
increase height and width of camera frustum they will occupy the same
number of pixels.

Best regards,
Andrey Ivanov


On Fri, 14 Dec 2018 at 19:41, David E DeMarle <dave.demarle at kitware.com>
wrote:

> Will turning off perspective do what you want?
>
> https://www.vtk.org/doc/nightly/html/classvtkCamera.html#a5b0e647798e7f45d358d8039ff41b378
> void vtkCamera::SetParallelProjection(vtkTypeBool
> <https://www.vtk.org/doc/nightly/html/vtkABI_8h.html#a663dee2c85b2a185fb34cb877d5208da>
>  flag)
>
> David E DeMarle
> Kitware, Inc.
> Principal Engineer
> 21 Corporate Drive
> Clifton Park, NY 12065-8662
> Phone: 518-881-4909
>
>
> On Fri, Dec 14, 2018 at 10:55 AM Andrey Ivanov <andrei.ivanov at phystech.edu>
> wrote:
>
>> Hello!
>>
>> I am trying to draw a lot of objects with the same shape for CAD system.
>> Let it be stars or circles for example.
>> The number of such circles can be about 1000-10000.
>> I would like to *preserve their size* when moving the camera, scaling
>> frustrum and changing distance to objects.
>>
>> For now I found two approaches:
>>
>> 1. Use vtkDistanceToCamera
>> An example from
>> https://lorensen.github.io/VTKExamples/site/Cxx/Visualization/DistanceToCamera/
>> is great
>> for low number of objects, however when their numer grows, the interface
>> starts to freeze due to
>> rescaling of shapes on each interaction with camera.
>>
>> 2. Use points (squares with width equal to 4 pixels).
>> It works fast and points size is fixed, but I would like to have more
>> complex shapes, like triangles and circles.
>>
>>
>> Is there another approach to solve this problem? It seems that with pure
>> OpenGL this can be implemented rather efficiently,
>> so I am looking for a way to do it in VTK.
>>
>> Best regards,
>> Andrey Ivanov
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