[vtkusers] Relationship between MinZBound and Position for a vtkVolume

[Elvis Stansvik]

2016-09-16 14:15 GMT+02:00 Elvis Stansvik <elvis.stansvik at orexplore.com>:
> 2016-09-16 13:26 GMT+02:00 Elvis Stansvik <elvis.stansvik at orexplore.com>:
>> This is a very basic question, but I feel like I've missed something
>> fundamental.
>>
>> I have a volume which I set the position for using SetPosition. I'm
>> not applying any other transformations such as rotation or scale.
>>
>> What surprises me is that after having set the position, if I look at
>> the MinZBound of the volume, it doesn't correspond to the Z position I
>> set.
>>
>> E.g. if I (after I set the position of the volume) do
>>
>>     qDebug() << "MinZBound:" << volume->GetMinZBound();
>>     qDebug() << "Position[3]" << volume->GetPosition()[2];
>>
>> I can get output such as:
>>
>>     MinZBound: -0.162738
>>     Position[3] -0.165138
>>
>> I thought that the bounds of a volume was in VTK world coordinates. If
>> so, shouldn't MinZBound be exactly the Z position?
>>
>> Thanks for any clarifications, I've probably missed something simple.
>
> I forgot to say that in the X and Y axes, there seems to always be a
> correspondance after my SetPosition(..):
>
> MinXBound: -0.0299
> Position[0] -0.0299
> MinYBound: -0.0299
> Position[1] -0.0299
>
> I can't see what's special about the Z direction. What else affects
> the bounds of the vtkVolume? The reason I'm asking, and what made me
> discover this, is that my volumes don't show up at the positions I
> expect them to.
>
> I'm sure I've missed something trivial, but I'm at a loss as to what it is :/

A perhaps important piece of information is that the vtkVolume uses a
vtkImageData that was the result of a vtkExtractVOI (taking a piece of
the image in the Z direction). So.. is there something special I
should watch out for regarding the bounds of the resulting image when
using vtkExtractVOI?

I found this old and unanswered post from 2006 where someone else was
seeing strange bounds after a vtkExtractVOI:

    http://www.vtk.org/pipermail/vtkusers/2006-December/039113.html

Or perhaps that poster also suffers from the same confusions I am at the moment?

Elvis

>
> Elvis
>
>>
>> Elvis