[vtkusers] Difficulty keeping volume within vtkBoxWidget

[Zamir Khan]

I should add: even purely scaling the box to a smaller size, with the 
right mouse button, will cause the volume to leave the box. It seems 
that they are not centered on the same point. I have verified that the 
volume remains in place - both position and origin remain at (0,0,0) - 
is it possible that the box's scaling is not centered on (0,0,0), even 
though it was bounded to the volume through SetProp3D()?

Zamir Khan wrote:
> Thanks for the response. I would like to continue to allow rotation,
> could I perhaps apply an inverse of the box transform to its bounds and
> then use that for cropping? Also, the reason that translation fails, I
> believe, is that when you grow or shrink one of the faces of the box,
> this appears to be a scaling & translation operation and, perhaps
> because I am always negating the scaling operation in my transform on
> the volume, by moving the faces of the box back and forth, I can get the
> volume to leave the bounds of the box.
>
> I will keep trying some different solutions (unfortunately disabling
> rotation is not an acceptable one for my application), but if anyone has
> accomplished this task before (with or without a vtkBoxWidget!) -
> example code would be much appreciated.
>
> Thanks,
> Zamir
>
> Karthik Krishnan wrote:
> > On Mon, Dec 7, 2009 at 5:26 PM, Zamir Khan <zkhan at modusmed.com> 
> <mailto:zkhan at modusmed.com%3E>
> > <mailto:zkhan at modusmed.com%3E> <mailto:zkhan at modusmed.com%3E%3E> wrote:
> > > Hi all,
> > >
> > > I have been attempting to use a vtkBoxWidget for what appears to be
> > a fairly
> > > common task: bounding and cropping a volume. My end goal is to have
> > the all
> > > user actions (translation, rotation) on the box be passed onto the
> > volume
> > > within, except for scaling. When the box is scaled, I need the
> > volume within
> > > to remain the same size, but be cropped by the planes of the box.
> > >
> > > I have been attempting to accomplish this with the following code (C#
> > > snippets, using Activiz.NET personal edition):
> > >
> > > // this callback gets called on the vtkBoxWidget's (outlineBox)
> > > InteractionEvt
> > > private void transformCallback( vtkObject sender,
> > vtkObjectEventArgs e
> > > )
> > > {
> > > vtkTransform boxTransform = vtkTransform.New();
> > > outlineBox.GetTransform( boxTransform );
> > >
> > > // remove the scaling from the transform before passing it on
> > > double[] scale = boxTransform.GetScale();
> > > boxTransform.Scale( 1.0 / scale[ 0 ], 1.0 / scale[ 1 ], 1.0 /
> > > scale[ 2 ] );
> > > volume.SetUserTransform( ( vtkLinearTransform )
> > boxTransform );
> > >
> > > // crop the volume
> > > vtkPlanes planes = vtkPlanes.New();
> > > outlineBox.GetPlanes(planes);
> > > double[] bounds = planes.GetPoints().GetBounds();
> > > volumeMapper.SetCroppingRegionPlanes( bounds[ 0 ], bounds[ 1 ],
> > bounds[ 2 ],
> > > bounds[ 3 ], bounds[ 4 ], bounds[ 5 ] ); }
> > >
> > > Now, a few things go wrong with this (probably over-simplified)
> > > implementation.
> > >
> > > 1) The volume does not stay within the box for all manipulations. 
> I have
> > > tried various approaches to remedy this, including not allowing
> > translation
> > > on the box (which is not critical to my application), but even so, I
> > have
> > > not been able to come up with a solution that guarantees that the 
> volume
> > > stays inside the box.
> >
> > See answer to (2) below..
> >
> >
> > >
> > > 2) The cropping does not always occur on the expected plane. When I
> > take a
> > > particular plane on the box and shrink the box w.r.t. that plane,
> > especially
> > > after having rotated the box, the volume will be cropped, but on it's
> > > corresponding plane. It appears that the "bounds" coordinates of 
> the box
> > > that I am passing to the mapper are not in agreement with the volume
> > - am I
> > > missing a transformation?
> >
> > The bounds specified via
> > volumeMapper.SetCroppingRegionPlanes()
> >
> > specify an axis-aligned aligned bounding box. You mention below that
> > they are out of sync after rotating the box, which is natural, since
> > the box widget no longer remains axis-aligned. Disable rotation on it.
> >
> > Translation should have worked just fine.. Perhaps a bug in your code..
> > ------------------------------------------------------------------------
>
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