[vtk-developers] bounds calculation in vtkActor

[Aashish Chaudhary]

Bill,

On Wed, Oct 27, 2010 at 8:35 PM, Bill Lorensen <bill.lorensen at gmail.com> wrote:

What Rusty (in his reply) +

> Rusty,
>
> I would think it should be consistent across ImageActor and Volume.

I agree but I guess it would be nice to know if someone else ran into
similar issues (yes / no). It is hard to imagine though but not
impossible. When I worked on a project (8 months back with Rusty) I
took control over the matrix multiplication and division by
homogeneous coordinate and hence this problem never showed up.

> I
> also suggest you push it to Gerrit for code review. And you should
> provide or modify a test to illustrate it.

Would you prefer test to go to the Gerrit or  in the email thread?
>
> Bill
>
> On Wed, Oct 27, 2010 at 8:29 PM, Rusty Blue <rusty.blue at kitware.com> wrote:
>> Folks,
>>
>>
>>
>> We're setting the UserMatrix of an actor to... surprise, surprise...
>> transform the actor.  Nothing exciting, right?
>>
>>
>>
>> Wrong, because the last row of our matrix is not the trivial [0 0 0 1].
>> This is handled well enough in OpenGL, but the bounds calculation (in
>> vtkActor::GetBounds()) is seriously wrong because it is doing a linear
>> transformation of the bbox it gets from the mapper (Transform is a
>> vtkLinearTransform):
>>
>>
>>
>>     fptr = bbox;
>>
>>     for (n = 0; n < 8; n++)
>>
>>       {
>>
>>       this->Transform->TransformPoint(fptr,fptr);
>>
>>       fptr += 3;
>>
>>       }
>>
>>
>>
>> The easiest fix I found for the issue was the following (force call to
>> InternalTransformPoint of vtkHomogeneousTransform):
>>
>>
>>
>>     fptr = bbox;
>>
>>     this->Transform->Update();
>>
>>     for (n = 0; n < 8; n++)
>>
>>       {
>>
>>
>> this->Transform->vtkHomogeneousTransform::InternalTransformPoint(fptr,fptr);
>>
>>       fptr += 3;
>>
>>       }
>>
>>
>>
>> The change doesn't cause any tests to fail (for me)... and it seems like a
>> reasonable change (perhaps should be made in vtkImageActor and vtkVolume as
>> well?)... but I wanted to put it out there (before I committed and pushed
>> the change), because it is seriously likely that I'm not considering some
>> other special "situations", or perhaps the "right" way to fix this, or ????
>>
>>
>>
>> Rusty
>>
>>
>>
>>
>>
>> _______________________________________________
>> Powered by www.kitware.com
>>
>> Visit other Kitware open-source projects at
>> http://www.kitware.com/opensource/opensource.html
>>
>> Follow this link to subscribe/unsubscribe:
>> http://www.vtk.org/mailman/listinfo/vtk-developers
>>
>>
>>
> _______________________________________________
> Powered by www.kitware.com
>
> Visit other Kitware open-source projects at http://www.kitware.com/opensource/opensource.html
>
> Follow this link to subscribe/unsubscribe:
> http://www.vtk.org/mailman/listinfo/vtk-developers
>
>



-- 
| Aashish Chaudhary
| R&D Engineer
| Kitware Inc.
| www.kitware.com