[vtkusers] GDCM2 + VTK: wrong slice order?

[Paul Melis]

Hello,

I'm using VTK 5.2 together with GDCM 2.0.10 to read in a set of MR 
slices in DICOM format. I was under the impression that the 
vtkGDCMImageReader would sort the files given to it (through 
SetFileNames()) at least by looking at the "Image Position (Patient)" 
tag. However, it seems that when I shuffle list of filenames in a random 
order before giving them to the reader the output of the reader changes 
and I can see the slices appear in the wrong order. I.e., something like 
this

#!/usr/bin/env python
import os, sys, random
import vtk
import vtkgdcm

files = sys.argv[1:]
random.shuffle(files)

sa = vtk.vtkStringArray()
for f in files:
    sa.InsertNextValue(f)

dr = vtkgdcm.vtkGDCMImageReader()
dr.SetFileNames(sa)
dr.Update()

dw = vtk.vtkDataSetWriter()
dw.SetFileName('out.vtk')
dw.SetInputConnection(dr.GetOutputPort())
dw.Write()

produces radically different output across different runs (observed by 
loading them in paraview and browsing the slices).

So this would suggest that my set of DICOM images does not contain 
enough information for them to be correctly sorted by GDCM. However, 
when I check the "Image Position (Patient) (0020,0032)" tag of the files 
these seem to make sense. So what else could be going on here? Any 
strategies to debug why these slices aren't getting ordered correctly?

Thanks,
Paul