[vtkusers] Re: vtkTransform again....transforming a point does not work as expected...simple example

[Anja Ende]

So basically the whole thing boils down to identifying the correct
transforms for generating the image coordinates to display coordinates.

I am pretty sure this is a common operation... but has me bamboozled...

So, again this is what I am doing at the moment...

void MyViewer::ImageToDisplaySpace(double x, double y, double z, double
out[4])
{
            // Transform the point using the inverse....
            double * tp = m_transform->GetLinearInverse()->TransformPoint(x,
y, z);
           // Get the reslice axes matrix...
            vtkMatrix4x4 * resliceMat = this->m_slicer->GetResliceAxes();
            out[0] = tp[0];
            out[1] = tp[1];
            out[2] = tp[2];
            out[3] = 0.0;

            resliceMat->Invert(resliceMat, m_indexInv);
            // Multiply the transformed point with the reslice axes
            m_indexInv->MultiplyPoint(out, out);
}

This works perfectly ok, as long as I am only shifting the reslice axes
origins (no rotations)... However, as soon as rotations come into play... I
feel like crying...everything is messed up...

I am going home for today... Please if you read this and have any ideas of
what I need to do...let me know.. I will bake you a cake!

Thanks,

Anja


On 23/09/06, Anja Ende <anja.ende at googlemail.com> wrote:
>
> Hi,
>
> Another thing that I noticed is that after rotation the image seems to
> jump or internally translate..... However, the position of the actor remains
> the same.... This probably also affects my calculations as I try to
> transform the points to display space correctly...
>
> So, again if someone could suggest how I can adjust to this affect... it
> would be great...
>
> Cheers,
> Anja
>
> On 23/09/06, Anja Ende < anja.ende at googlemail.com> wrote:
> >
> > Ok, I have finally managed to get something working that works for
> > normal transformation to the image->Display and vice versa...
> >
> > However, it returns bogus values when a slice is rotated along an
> > axis...
> >
> > -------------------------------------------------------------------------------------------------------
> >
> > Display ->Image Space...
> >
> > // x, y, z are display coordinates
> >
> > vtkMatrix4x4 * resliceMat = this->m_slicer->GetResliceAxes();
> > double axesTransform[4] = {x, y, z, 0.0};
> > resliceMat->MultiplyPoint(axesTransform, axesTransform);
> > double * tp = m_transform->TransformPoint(axesTransform[0],
> > axesTransform[1], axesTransform[2]);
> >
> > // Out will contain the image coordinates
> >
> > out[0] = tp[0];
> > out[1] = tp[1];
> > out[2] = tp[2];
> > out[3] = 0.0;
> >
> >
> > --------------------------------------------------------------------------------
> > // Image->Display Space
> > This function works if the slice is not rotated...However, if the slice
> > is rotated then the values are incorrect... I do not understand why as the
> > rotation is reflected in the transformation matrix.
> >
> > // x, y, z are image coordinates
> > // out will contain the values in the display space... or so I hoped!
> >
> > double * tp = m_transform->GetLinearInverse()->TransformPoint(x, y, z);
> > vtkMatrix4x4 * resliceMat = this->m_slicer->GetResliceAxes();
> > out[0] = tp[0];
> > out[1] = tp[1];
> > out[2] = tp[2];
> > out[3] = 0.0;
> > resliceMat->Invert(resliceMat, m_indexInv);
> > m_indexInv->MultiplyPoint(out, out);
> > ---------------------------------------------------------------------------------------------
> >
> >
> > I am really struggling with this, so any help would be really nice!
> >
> > Thanks,
> > Anja
> >
> > On 23/09/06, Anja Ende < anja.ende at googlemail.com> wrote:
> > >
> > > So, trying to use the reslice transform and reslice axes as suggested
> > > by David:
> > >
> > > I have an image with the following dimesnions: 256 X 256 X 62. It has
> > > been centered using vtkImageChangeInformation...
> > >
> > > It has been scaled using the vtkTransform object by a factor of 2 in
> > > the X and Y direction..
> > >
> > > So, the transform matrix looks like this:
> > >
> > >   0.5 0 0 0
> > >   0 0.5 0 0
> > >   0 0 1 0
> > >   0 0 0 1
> > >
> > >
> > > So, I click on the center of the image and I expect that the
> > > transformation back should give me the imnage coordinates in the original
> > > input image. So, I do the following:
> > >
> > > Input :255: 255: 62 (in pixels). Ignore the Z value... always 62
> > >
> > > vtkImageData * in = reinterpret_cast<vtkImageData
> > > *>(this->m_slicer->GetInput());
> > > in->UpdateInformation();
> > >
> > > double origin[3];
> > > double spacing[3];
> > > in->GetOrigin(origin);
> > > in->GetSpacing(spacing);
> > >
> > > // x = 255, y = 255, z = 62
> > > // converting to world coordinates
> > > double xt = origin[0] + spacing[0] * x;
> > > double yt = origin[1] + spacing[1] * y;
> > > double zt = origin[2] + spacing[2] * z;
> > >
> > > // Now transform the points....
> > > double * tp = m_transform->TransformPoint(xt, yt, zt);
> > >
> > > // Reslice axes of my reslicer
> > > vtkMatrix4x4 * resliceMat = this->m_slicer->GetResliceAxes();
> > >
> > > // converting the transformed points back to display coordinates
> > > double bx = (tp[0]  - origin[0]) / spacing[0];
> > > double by = (tp[1]  - origin[1]) / spacing[1];
> > > double bz = (tp[2]  - origin[2]) / spacing[2];
> > >
> > > double inout[4] = {bx, by, bz, 0.0};
> > > resliceMat->MultiplyPoint(inout, inout);
> > >
> > > Now, I expected this to return:
> > >
> > > 127.5: 127.5: 62...center of the data...
> > >
> > > Instead it returns:
> > >
> > > 191.75: 191.25: 62 :((((
> > >
> > > I know I am making some fundamental errors here...so if someone could
> > > please help me sort it out... I would be really grateful
> > >
> > > Best,
> > >
> > > Anja
> > >
> > >
> > >  On 22/09/06, Anja Ende <anja.ende at googlemail.com> wrote:
> > > >
> > > > Yes, I, unfortunately, could not get any other way to work... As I
> > > > said, I am trying to get the TransformPoints method to work, but with little
> > > > success so far.
> > > >
> > > > Could you point an example as to how to use the ResliceTransform and
> > > > the ResliceMatrix??
> > > >
> > > > Cheers and thanks,
> > > >
> > > > Anja
> > > >
> > > > On 22/09/06, David Gobbi < dgobbi at atamai.com> wrote:
> > > > >
> > > > > I should point out that the IndexMatrix is not a public member of
> > > > > the
> > > > > class... and if you have a special version of vtkImageReslice that
> > > > > makes
> > > > > this member public, you are using vtkImageReslice in a way that
> > > > > other
> > > > > people don't.
> > > > >
> > > > > Why not just use the ResliceTransform and ResliceMatrix?
> > > > >
> > > > > - David
> > > > >
> > > > >
> > > > >
> > > > > Anja Ende wrote:
> > > > > > Forgot to mention...
> > > > > >
> > > > > > I am using the index matrix in the vtkImageReslice class to do
> > > > > the
> > > > > > input->output mapping and vice versa (by using the inverse of
> > > > > the
> > > > > > matrix).
> > > > > >
> > > > > > Anja
> > > > > >
> > > > > ------------------------------------------------------------------------
> > > > > >
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