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

[Anja Ende]

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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