[vtkusers] Rotating a vtk actor using world coordinates

[David Gobbi]

Hi Chiranjib,

The actor's Rotate methods are inherited from vtkProp3D, but the code that
you
show is from vtkTransform.

The actor's RotateWXYZ method commutes the matrices (i.e. multiplies them in
a different order) as compared to the RotateX,Y,Z methods.  The original
author
might have had a reason for doing this, but I doubt it was a good enough
reason
to justify the confusion that this method causes...

You can use SetUserMatrix as follows:

actor->SetUserMatrix(transform->GetMatrix());

 - David


On Tue, Sep 29, 2015 at 4:46 AM, Chiranjib Sur <sur.chiranjib at gmail.com>
wrote:

> Hi,
> The implementation of the rotation transform are as follows (from
> vtkTransform.h file : URL
> https://github.com/Kitware/VTK/blob/master/Common/Transforms/vtkTransform.h
> )
>
> void RotateX(double angle) { this->RotateWXYZ(angle, 1, 0, 0); }; void
> RotateY(double angle) { this->RotateWXYZ(angle, 0, 1, 0); }; void RotateZ(
> double angle) { this->RotateWXYZ(angle, 0, 0, 1); }; Therefore, how there
> going to be a difference between
>
> actor->RotateX(45);
> actor->RotateY(45);
>
> and
>
> actor->RotateWXYZ(45, 1, 0, 0);
> actor->RotateWXYZ(45, 0, 1, 0);
>
> Can anyone please explain this a bit? David, Is there any example of the
> SetUserMatrix() available to learn about it?
>
> Thanks,
> Chiranjib
>
> On Mon, Aug 10, 2015 at 10:38 PM, David Gobbi <david.gobbi at gmail.com>
> wrote:
>
>> Hi Drak,
>>
>> Generally it's better design to build a transform or matrix and then
>> apply that to the actor via SetUserTransform() or SetUserMatrix().  That
>> way, the transform or matrix is available to you if you have to move other
>> points or actors between coordinate systems.
>>
>> To rotate around a point in space, you have to apply a translation to put
>> that point at the origin, then do the rotation, and then translate back
>> again.
>>
>>  - David
>>
>> On Mon, Aug 10, 2015 at 10:53 AM, Drak <draktharrblorf at gmail.com> wrote:
>>
>>> I should add that I'm using the vtkImageActor with a vtkImageData as a
>>> source. It seems that my point of rotation is the bottom left of my image
>>
>>
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