[vtkusers] question about "ImageSlicing.cxx"

Tue Nov 11 13:23:40 EST 2008

Thank you David,

I am going to inquire about vtkCamera and vtkViewPort to better
understand...

I completely agree with you with the fact that I can easily resolve the
problem of my example with a simple zoom of the camera...

=> if I was sure to be in the case 1 (27,5 < 60), I could resolve all my
problems with a zoom, and after that it would be easy to convert the
coordinates of the window(mouse) to coordinates of the images.

But what about the case 2 (80>60)...?
Even if I do a "negative zoom", I have the impression that it would be "too
late", I mean the image had already been cropped and a "negative" zoom would
just display new black borders top and down (instead of the 10 cm top and
down of the coronal image)

I hope you understand, it's not so easy to explain...

Concerning this case, I just wanted to ask you a last question...

I think I found something interresting in the vtkImageReslice documentation
(
http://www.vtk.org/doc/nightly/html/classvtkImageReslice.html#ce80eced5f32389efe97e72612dec960)
:

virtual void vtkImageReslice::SetAutoCropOutput ( int
 )  [virtual]

Turn this on if you want to guarantee that the extent of the output will be
large enough to ensure that none of the data will be cropped (default: Off).

I'm a newbie in vtk and I wanted to have your opinion : don't you think it's
what I'm looking for (to resolve the "case 2")?

I think it's the last time that I annoy you today with my problem ;-)

Have a very nice day,

Stéphane

2008/11/11 David Gobbi <david.gobbi at gmail.com>

> Hi Stephane,
>
> I think that I understand what you are trying to do, but I really
> think that your problem is because of the camera and not because of
> vtkImageReslice.
>
> The output of vtkImageReslice does have its own physical coordinate
> system: if we say that matrix "A" is the ResliceAxes, and (x,y,z)
> define the physical space of the axial image, and (x',y',z') define
> the physical space of the coronal image, the the following simple
> equation holds true:
>
>  [x;y;z] = A [x';y';z']  (pretend these are column vectors)
>
> In this equation, (x,y,z) and (x',y',z') are real physical coordinates
> (i.e. in millimetres).
>
> These real, physical coordinates are being mapped to screen
> coordinates according to transformations that are done by the
> vtkCamera and by the ViewPort of the renderer.  Unless you understand
> what the Camera and ViewPort are doing, you won't be able to map mouse
> coordinates to physical coordinates.
>
>   David
>
> On Tue, Nov 11, 2008 at 10:37 AM, Stéphane CALANDE <scalande at gmail.com>
> wrote:
> > Thank you David, I'll try to change the background.
> >
> > But in fact, even if I saw that the borders were red, it wouldn't resolve
> my
> > problem. I'm going to explain you why...
> >
> >
> > Here's what I'd like :
> >
> > If I call something like :
> >
> > "window.SetSize(x,y)" (with x,y proportionnal to 60 x 27.5 => if you
> > remember it is the real proportions of the coronal image)
> >
> > Have a look at http://info.fundp.ac.be/~scalande/borders2.PNG<http://info.fundp.ac.be/%7Escalande/borders2.PNG>to
> > understand...
> >
> >
> >
> > It is so important for me because I'm creating an interface that allow
> the
> > select a region of the image with the mouse...
> > So I have to do a conversion between the mouse coordinates and the image
> > coordinates.
> >
> >
> > I've another thing to say. In my example, the height of the coronal image
> is
> > smaller than the height of the axial image. (60 > 27.5)
> > And so there are borders... But if it was the contrary, if the coronal
> image
> > height was 80, for example...
> >
> > Would the image be croped of 10 on top and 10 on down?
> >
> >
> > To avoid the borders in the first case (<60) and the possible crop in the
> > second case (>60), it would be really nice if the coronal views created
> by
> > ImageReslice were represented in their own "physical space" (instead of
> the
> > axial views physical space).
> >
> >
> >
> > Do you understand better ?
> >
> >
> >
> > I thank you one more time for the help,
> >
> >
> >
> > Stéphane
> >
> >
> >
> > 2008/11/11 David Gobbi <david.gobbi at gmail.com>
> >>
> >> Hi Stephane,
> >>
> >> When you get back to you office, try setting the background of the
> >> renderer to red and I'm sure that you will see that the borders are
> >> not part of the image.
> >>
> >> The reason that the borders don't disappear when you resize the window
> >> is that everything in the vtkRenderer gets resized when you resize the
> >> window.  That is always the behavior of vtkImageActor or any other
> >> actor that is not a 2D actor: everything gets scaled relative to the
> >> window size.
> >>
> >>   David
> >>
> >>
> >>
> >> On Tue, Nov 11, 2008 at 9:29 AM, Stéphane CALANDE <scalande at gmail.com>
> >> wrote:
> >> > Hi vtk-list, hi David,
> >> >
> >> >
> >> >
> >> > Thank you very much for your answer.
> >> >
> >> > I had already fixed the problem of zoom (that is not 1.0 by default)
> >> > before.
> >> >
> >> > About the problem of the borders, I understand what you say, but I
> think
> >> > that the borders are "really" included in the image.
> >> > To be honnest, I can't try your advice beacuse I'm not in my office
> >> > today,
> >> > but I can give you other details to prove that the borders are
> included
> >> > in
> >> > the image.
> >> >
> >> > Even if I re-sized manually the window with the mouse (for example the
> >> > height), all the image (the coronal subject and the borders) are
> >> > proportionally reduced.
> >> >
> >> > (I've tinkered a PNG to explain this. Have a look at :
> >> > http://info.fundp.ac.be/~scalande/borders.PNG<http://info.fundp.ac.be/%7Escalande/borders.PNG>
> >> > But it's obviously not the real images because I'm not in my office
> >> > today,
> >> > it's just to give an example of the same effect...)
> >> >
> >> >
> >> > If the black borders were "just" the background, they should slowly
> >> > disappear during the re-sizing of the window... But it's not the
> case...
> >> >
> >> >
> >> > I really have the impression that the coronal views created by
> >> > ImageReslice
> >> > are represented in the same "physic space" than the basic axial views
> >> > (representing the volume).
> >> >
> >> >
> >> > Can my explanation help you to understand the problem?
> >> >
> >> >
> >> >
> >> > Thank you very much for your help,
> >> >
> >> >
> >> > Regards,
> >> >
> >> >
> >> >
> >> > Stéphane
> >> >
> >> >
> >> >
> >> >
> >> >
> >> >
> >> > 2008/11/10 David Gobbi <david.gobbi at gmail.com>
> >> >>
> >> >> Hi Stephane,
> >> >>
> >> >> The black borders that you see in this example are actually the
> >> >> background in the renderer.  If you add
> >> >> "renderer->SetBackground(1.0,0.0,0.0);" to the example, then you will
> >> >> see the black bars turn to red.
> >> >>
> >> >> In other words, it isn't vtkImageReslice that is adding these
> borders.
> >> >>  These borders are present because the RenderWindow is square, and
> >> >> vtkImageReslice has no control over the window size.
> >> >>
> >> >> So what you need to do is call window->SetSize() to set the size of
> >> >> the window to the size of your image.  You can call Update() on
> >> >> ImageReslice and get the size of its output, so that you know what
> >> >> size to make the window.
> >> >>
> >> >> Even after you do this, though, you will still have to do one more
> >> >> thing.  By default, the zoom factor for camera is not 1.0.  You will
> >> >> have to call add code like the following:
> >> >>
> >> >>  vtkCamera *camera = renderer->GetActiveCamera();
> >> >>  camera->SetViewAngle(2.0*atan(0.5*height_of_image/camera_distance));
> >> >>
> >> >> Alternatively, you can switch to parallel projections, which makes
> the
> >> >> math easier but I'm not sure if the VTK interactors all work properly
> >> >> in parallel mode:
> >> >>
> >> >>  camera->ParallelProjectionOn();
> >> >>  camera->SetParallelScale(height_of_image);
> >> >>
> >> >> I hope this is what you were looking for,
> >> >>
> >> >>    David
> >> >>
> >> >>
> >> >>
> >> >>
> >> >>
> >> >>
> >> >>
> >> >>
> >> >>
> >> >>
> >> >>
> >> >> On Mon, Nov 10, 2008 at 9:38 AM, Stéphane CALANDE <
> scalande at gmail.com>
> >> >> wrote:
> >> >> > Hi,
> >> >> >
> >> >> >
> >> >> > I'm trying "ImageSlicing.cxx" to display an "coronal" slice from a
> >> >> > volume
> >> >> > (multiple axial slices).
> >> >> >
> >> >> > It works well, but there is just a problem.
> >> >> >
> >> >> >
> >> >> > Information about my axial slices :
> >> >> >
> >> >> > SIZE : 512 x 512
> >> >> > SPACING : (1,17188 ; 1,17188)
> >> >> >
> >> >> > "REAL" SIZE = 60 cm x 60 cm
> >> >> >
> >> >> >
> >> >> > Information about the coronal slices that SHOULD be created
> >> >> >
> >> >> > SIZE : 512 x 55
> >> >> > SPACING : (1,17188 ; 5)
> >> >> >
> >> >> > "REAL" SIZE = 60 cm x 27.5 cm
> >> >> >
> >> >> >
> >> >> > But the problem is that the image created by "ImageSlicing" has the
> >> >> > shape of
> >> >> > a square.
> >> >> > I mean it has the same shape than the axial images.
> >> >> >
> >> >> > The representation of the coronal object is correct (good
> >> >> > proportions)
> >> >> > but
> >> >> > there are 2 black borders (top and down)
> >> >> >
> >> >> > Something like that :
> >> >> >
> >> >> > +++++++++++++++++++
> >> >> > +++++++++++++++++++
> >> >> > +++++++++++++++++++
> >> >> > ---CORONAL IMAGE---
> >> >> > ---CORONAL IMAGE---
> >> >> > ---CORONAL IMAGE---
> >> >> > +++++++++++++++++++
> >> >> > +++++++++++++++++++
> >> >> > +++++++++++++++++++
> >> >> >
> >> >> > ('+' = black)
> >> >> >
> >> >> > In fact, I'd like the image to have the proportion "60 x 27.5 "
> >> >> > (without
> >> >> > any
> >> >> > black borders...)
> >> >> >
> >> >> > ---CORONAL IMAGE---
> >> >> > ---CORONAL IMAGE---
> >> >> > ---CORONAL IMAGE---
> >> >> >
> >> >> >
> >> >> > Do you see what I mean ?
> >> >> >
> >> >> > I've searched in the methods of vtkImageReslice but I didn't find
> >> >> > what
> >> >> > I'm
> >> >> > looking for...
> >> >> >
> >> >> >
> >> >> >
> >> >> > Do you have any idea to help me ?
> >> >> >
> >> >> > Any help would be appreciated ;-)
> >> >> >
> >> >> > Thank you in advance !
> >> >> >
> >> >> >
> >> >> >
> >> >> > Stéphane
> >> >> >
> >> >> > _______________________________________________
> >> >> > This is the private VTK discussion list.
> >> >> > Please keep messages on-topic. Check the FAQ at:
> >> >> > http://www.vtk.org/Wiki/VTK_FAQ
> >> >> > Follow this link to subscribe/unsubscribe:
> >> >> > http://www.vtk.org/mailman/listinfo/vtkusers
> >> >> >
> >> >> >
> >> >
> >> >
> >
> >
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.vtk.org/pipermail/vtkusers/attachments/20081111/d046a226/attachment.htm>