[vtkusers] Using vtkExtractVOI with negative extent on a 2D vtkImageData

[Flo]

Dear all:

I actually solved my problem - maybe that s not the best way but I  
just post MY solution (maybe risky).

I made a  change round line 204 of vtkExtractVOI.cxx from outOrigin 
[i] - voi[2*i] ..... to outOrigin[i] = origin[i]
Then recompile VTK and I made sure the example TestImageTracerWidget  
was still working !

Then, to extract a ROI from the Spline considering a 2D  
vtkImageData,  one should modify the vtkImageTracerWidget and the  
vtkSplineWidget to the SetProjectionNormalToZAxes .... as well as the  
extruding vector nomal to the x,y plane, SetVector(0,0,1)

I was missing the update of the last extruding vector.

regards,
Flo.

On 7-Aug-07, at 4:33 PM, Flo wrote:

> Dear all:
>
> I'm using vtkExtractVOI to extract a Region of Interest such as  
> presented in TestImageTracerWidget.
> However, I'm using it to get a ROI out of a 2D vtkImageData  
> (through the ITK2VTK pipeline).
>
> I realized that the vtkExtractVOI does not work (at least for me)  
> with data's negative extent.
> The first thing I noticed was that the Spline Path (the ROI) was  
> always shifted from the original actor to the output actor. Thus, I  
> dug a little bit on vtkusers, saw some ppl reporting a bug - change  
> the line 202 of vtkExtractVOI to outOrigin[i] - origin[i] (one may  
> notice the comments of the vtk programmer - //We might as well make  
> this work for negative extents).
> This solved it and now both Spline ROI are localized identically on  
> both the input and output actor - As well, the VTK example  
> mentionned above still compiles and runs.
>
> HOWEVER, I'm still not able to extract the ROI, meaning I do have  
> the Spline path where it is supposed to be, but it does not extract  
> the ROI. I guess this is because I fixed my issue for a display,  
> but not for the overall extraction process.
>
> Am I the one ont using vtkExtractVOI correctly with a 2D  
> vtkImageData or is there an actual problem using it in such cases ?  
> Is there a fix ?
>
> regards,
> flo.
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