[vtkusers] vtkTransform::Concatenate followed by Inverse results in Identity (VTK 6.3.0)

[Torsten Sadowski]

Hi David,

no, Update() does not change the result. I came across this issue 
because I found the vtkTDxInteractorStyleCamera to be utterly useless. 
The reason is that this snippet from vtkTDxInteractorStyleCamera does 
nothing:

//Gettherotationaxisinworldcoordinates.

this->Transform->Identity();

this->Transform->Concatenate(eyeToWorld);

this->Transform->Inverse();

this->Transform->TransformVector(axisEye,axisWorld);

axisEye is identical to axisWorld. The vtkTDxInteractorStyleGeo has something similar.
There is either a bug in vtkTransform or in the InteractorStyles. I could make a bug report for either.

Cheers,
Torsten


Am 21.01.2016 um 18:04 schrieb David Gobbi:
> Hi Torsten,
>
> I suspect that it will work if you do this:
>
>   this->Transform->Identity();
> this->Transform->Concatenate(eyeToWorld->GetMatrix());
>   this->Transform->Inverse();
>
> The "Concatenate" method has two signatures with different behavior:
>   Concatenate(vtkMatrix4x4 *)
>   Concatenate(vtkTransform *)
>
> The second one establishes a connection between the two transforms,
> so if you do "this->Transform->Concatenate(eyeToWorld)" then any
> future changes to "eyeToWorld" will also cause "this->Transform" to
> change.
>
> If you call "this->Transform->Update()" before PrintSelf, is the correct
> matrix printed?  The TransformVector() method implicitly calls Update().
>
>  - David
>
>
> On Thu, Jan 21, 2016 at 9:28 AM, Torsten Sadowski 
> <torsten.sadowski at windnovation.com 
> <mailto:torsten.sadowski at windnovation.com>> wrote:
>
>     Hello,
>
>     I am trying to design my own vtkTDxInteractorStyle. When I looked
>     into vtkTDxInteractorStyleCamera as an example I found something
>     puzzling which might be a bug in either vtkTransform or
>     vtkTDxInteractorStyleCamera.
>
>     This snippet from voidvtkTDxInteractorStyleCamera::OnMotionEvent
>
>     //Gettherotationaxisinworldcoordinates.
>
>     this->Transform->Identity();
>
>     this->Transform->Concatenate(eyeToWorld);
>
>     this->Transform->Inverse();
>
>     this->Transform->TransformVector(axisEye,axisWorld);
>
>     does nothing useful because the Transform returns the identity after Inverse (checked with PrintSelf).
>     This on the other hand works:
>
>     //Gettherotationaxisinworldcoordinates.
>     this->Transform->SetMatrix(eyeToWorld->GetMatrix());
>     this->Transform->Inverse();
>     this->Transform->TransformVector(axisEye,axisWorld);
>
>     I'm baffled.
>
>     Best Regards,
>     Torsten Sadowski
>
>
>     -- 
>
>
>     Dr.-Ing. Torsten Sadowski
>     Turbine Design/System Integration
>
>     WINDnovation Engineering Solutions GmbH
>     Stralauer Platz 33-34
>     10243 Berlin
>     Germany
>     Phone: +49 30 547195 34 <tel:%2B49%2030%20547195%2034>
>     Fax: +49 30 547195 39 <tel:%2B49%2030%20547195%2039>
>     Managing directors:
>     Dr.-Ing. Roland Stoer, Dipl.-Ing. Albrecht Kantelberg
>     Registered at Amtsgericht Charlottenburg, HRB 110081 B
>
>     www.windnovation.com <http://www.windnovation.com>
>
>     Certified according to ISO 9001:2008
>
>

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