[vtkusers] vtk Coordinate system clarification

[Scott Johnson]

Hi Folks,

 

I'm running into issues trying to spatially coordinate the display of
images and polygons (spheres in this case).  My ultimate goal is to
express all coordinates in the DICOM Frame of Reference.

 

Right now I'm trying to display axial, sagittal, and coronal slices and
the intersection of those image planes with spheres.  I'm using
vtkImageReslice to slice the images, and vtkCutter to extract the
contours of the intersection, but am running into problems getting the
sliced polygons to show up in the right place with respect to the
images.  I can get the spheres to display in the correct location in a
MIP rendering.

 

My difficulty is understanding in what coordinate system everything but
images are expressed in.  (I've read the Coordinate System section in
the new version of the VTK User's guide.)  For example, if I set the
position of a vtkSphereSource with SetCenter is that in pixel
coordinates in the coordinate system, or is it an absolute location in
space?  The same goes for a vtkPlane:  What coordinate system should
locations passed to SetOrigin be in?

 

My thought was that everything was expressed in the World coordinate
system and the world coordinate system was established by the images,
but that doesn't seem to be working for me.

 

Thanks

 

                                -- Scott

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