[vtkusers] world coordinates and image data

[Kall, Bruce A.]

> However, if you are looking to transform the data itself, your only 
> option is to transform the imagedata to polys using 
> vtkImageDataGeometryFilter and then transforming this using 
> vtkTransformPolyDataFilter.

I have been able to accomplish what I think Richard original asked by using

vtkImageReslice *reslice;

I put the transform on this and it transforms all my image data which is 
not axis aligned into world
coordinates correctly.

Small snippet:
-----------------------------------------------------------------------------------------------------------------------------
volume_reader = vtkImageReader::New();
volume_reader->SetFileName(data_filename);
volume_reader->SetFileDimensionality(3);
volume_reader->SetDataExtent(0,(int) xsize - 1,0,(int)ysize - 1,0,(int) 
zsize - 1);
volume_reader->SetDataSpacing(voxel_size,voxel_size,voxel_size);
volume_reader->FileLowerLeftOn();
volume_reader->SetDataOrigin(origin);
volume_reader->SetDataScalarTypeToUnsignedChar();
volume_reader->SetDataByteOrderToBigEndian();

/* You may or may not need a permutation matrix here to have your volume 
put in */
/* correctly. Mine starts at the upper left and not lower left */
permutation_xform = vtkTransform::New();
permutation_matrix = vtkMatrix4x4::New();
permutation_matrix->Identity();
permutation_matrix->SetElement(1,1,-1);
permutation_matrix->SetElement(2,2,-1);
permutation_xform->SetMatrix(permutation_matrix);
volume_reader->SetTransform(permutation_xform);

reslice_matrix = vtkMatrix4x4::New();
/* stuff in your transform here */
reslice_xform = vtkTransform::New();
reslice_xform->SetMatrix(reslice_matrix);
reslice = vtkImageReslice::New();
reslice->SetInputConnection(volume_reader->GetOutputPort());
reslice->SetResliceTransform(reslice_xform);

image_volume = vtkVolume::New();
volume_raycast_mapper = vtkFixedPointVolumeRayCastMapper::New();
volume_raycast_mapper->SetInputConnection(reslice->GetOutputPort());
image_volume->SetMapper(volume_raycast_mapper);
renderer->AddVolume(image_volume);
----------------------------------------------------------------------------------------------------------------------

This works for me.

Bruce


Karthik Krishnan wrote:
> On Wed, Feb 25, 2009 at 11:11 PM, Richard Beare 
> <richard.beare at gmail.com <mailto:richard.beare at gmail.com>> wrote:
>
>     Hi,
>     I'm trying to track down appropriate vtk data representations for
>     displaying multiple image data sets in correct relationships to one
>     another. The source data is MRI slices.
>
>     Does the vtkImageData type have the option of image axes not being
>     aligned to world coordinates?
>
>
> no
>  
>
>     Assuming this isn't possible, what is the most appropriate data
>     structure to use. The approach I'm thinking of is to iterate over the
>     image in ITK, looking up world coordinates for each voxel, and
>     building a large vtk data structure that I'd then save in a paraview
>     compatible format.
>
>
> We tend to keep the image data in its local (axis aligned) coordinate 
> system. You can manage local to world coordinate system mapping at the 
> actor level by setting a user transform (see SetUserTransform) on the 
> actor visualizing your data. 
>
> However, if you are looking to transform the data itself, your only 
> option is to transform the imagedata to polys using 
> vtkImageDataGeometryFilter and then transforming this using 
> vtkTransformPolyDataFilter.
>
>
>
>     Any recommendations?
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> -- 
> Karthik Krishnan
> R&D Engineer,
> Kitware Inc.
> Ph: 518 371 3971 x119
> Fax: 518 371 3971
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