[vtkusers] vtkImageViewer2 show zoom factor and visible coordinates

[Dean Inglis]

Hi Christian,

the way you  are using vtkCoordinate looks reasonable to me ...

- Dean


On Thu, Sep 12, 2013 at 12:15 PM, Christian Lackas <lackas at invicro.com>wrote:

> * Dean Inglis <inglis.dl at gmail.com> [130912 10:05]:
>
> Dear Dean,
>
> thanks for your vtkCoordinate hint, this go me on the right track again.
>
> I now do this to calculate the zoom with which my image is displayed:
>
>     float getZoom( vtkRenderer *R, vtkImageData *I ) {
>         int *dim = I->GetDimensions();
>         vtkSmartPointer<vtkCoordinate> c = vtkCoordinate::New();
>         c->SetValue( 0, 0, 0 );
>         int *res = c->GetComputedDisplayValue( R );
>         int a = res[0];
>         c->SetValue(dim[0], 0, 0);
>         res = c->GetComputedDisplayValue( R );
>         return static_cast<float>(res[0]-a)/dim[0];
>     }
>
> This is what you had in mind, right, or am I still doing this overly
> complicated?
>
> Adding another image actor for the small preview is also a good idea, will
> look
> into this.
>
> Christian
>
> --
> Dr. Christian Lackas, Managing Partner
> inviCRO, LLC -- In Imaging Yours
> http://www.invicro.com/  http://www.spect-ct.com/
>
> > Hi Christian,
> >
> > I wrote a class for querying image pixel/voxeld data a while back and I
> > could make it available
> > to you off-line at your request.
> > In the meantime, have a look at http://www.vtk.org/Wiki/VTK/Examples/Cxxin
> > particular
> > http://www.vtk.org/Wiki/VTK/Examples/Cxx/Images/PickingAPixel2
> > and
> > http://www.vtk.org/Wiki/VTK/Examples/Cxx/Images/PickingAPixel
> >
> > For displaying a minimap, I would try adding a second vtkRenderer with a
> > smaller viewport
> > in your main vtkRenderWindow and place a vtkImageActor within it.
> >
> > To compute zoom, have a look at vtkCoordinate class, which allows
> conversion
> > between numerous kinds of coordinate types (viewport, normalized
> viewport,
> > world etc.),
> > probably make use of the extrema of your viewing window and those of the
> > image.
> >
> > Dean
> >
> >
> >
> > On Thu, Sep 12, 2013 at 4:47 AM, Christian Lackas <lackas at invicro.com
> >wrote:
> >
> > > Hi Everybody,
> > >
> > > I display a large 2D image (larger then typical screen resolutions) in
> a
> > > a vtkImageViewer2 and would like to give the user some guidance as to
> > > which part she is currently looking at.
> > >
> > > My questions are:
> > > * What is the easiest way to get the zoom (ratio of image to world
> pixels)?
> > > * How can I get the coordinates (in image pixels) of the par of the
> > >   image that is currently visible?
> > >
> > > Details:
> > >
> > > In a first steps, I would like to show the zoom level (100% = one pixel
> > > on screen contains exactly one pixel of the image). I looked at
> > > vtkCamera and found the Zoom(double) function, pointing me to
> > > ParallelScale() (ParallelProjection: On), and this variable seems to be
> > > indeed related to the zoom (larger values indicate lower zoom),
> however,
> > > I was not able to derive an absolute number from this (e.g. 50%, so two
> > > image pixels are shown in 1 pixel on screen). In my example 100% is
> > > around ParallelScale=140.
> > > Also vtkCamera::Get(Model)ViewTransformObject()->GetScale() does not
> > > work (always returns 1,1,1).
> > > I tried to use vtkCamera's Print(stream) method, however, could not
> find
> > > any other values that change with the zoom, and I could not figure out
> > > how to use GetProjectionTransformObject(double,double,double) properly.
> > >
> > > In a next step, I would like to show a small minimap in one corner,
> just
> > > consisting of two rectangles showing the full image and the current
> view
> > > port. For this I would need to know which coordinates (in image pixels)
> > > are currently shown.
> > > Unfortunately, ImageActors DisplayExtent just contains the full
> > > dimensions, and I have not found any other value that seems to be
> useful
> > > (also not in vtkCamera).
> > >
> > > Any help on this is highly appreciated.
> > >
> > > Thanks,
> > >  Christian
> > >
> > > --
> > > Dr. Christian Lackas, Managing Partner
> > > inviCRO, LLC -- In Imaging Yours
> > > http://www.invicro.com/  http://www.spect-ct.com/
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