[Paraview] Interpretation of histogram of deformation field magnitude?

[motes motes]

I have now followed your advise and I no longer get negative values
which is good. But I still cannot make any sense out of the histogram.

I have tried to make a histogram showing the following 3 types of information:

1) bin_values
http://37133.vs.webtropia.com/apache2-default/test/hist1.jpg

2) GlyphVector_total (Magnitude)
http://37133.vs.webtropia.com/apache2-default/test/hist2.jpg

3) GlyphVector_average (Magnitude)
http://37133.vs.webtropia.com/apache2-default/test/hist3.jpg

As I understand the magnitude of the vectors are shown along the
x-axis. This means that no vectors have 0 magnitude and the max
magnitude is 5.11 units.

But what is plotted along the y-axis? The input image contains
512*512= 262144 pixels. But the sum of the blocks in the above
histograms exceeds this number so it cannot be the pixel count. What
is plotted along the y-axis?





On Wed, Nov 4, 2009 at 1:30 PM, Utkarsh Ayachit
<utkarsh.ayachit at kitware.com> wrote:
> On the properties panel for the Histogram filter, you choose the array
> to generate histogram from. Currently the panel doesn't not support
> selecting the magnitude of a vector array (only 1 component). In your
> case, by default the 0th component of the GlyphVector is chosen, which
> can be negative and hence the plot.
>
> To generate a histogram for the magnitude of the vector, apply another
> calculator with the expression:
>
> mag(GlyphVector)
>
> and then generate a histogram using the "Result" array.
>
> Utkarsh
>
> On Tue, Nov 3, 2009 at 8:15 PM, motes motes <mort.motes at gmail.com> wrote:
>> I have loaded a deformation field (.mhd file) in paraview made with itk:
>>
>> 1) open .mhd file
>> 2) connect the calculate and use the below expression:
>>
>>  MetaImage_X*iHat+MetaImage_Y*jHat+0*kHat
>>
>> 3) Add glyph filter.
>>
>> The result looks like this:
>>
>> http://37133.vs.webtropia.com/apache2-default/test/deform.png
>>
>>
>> But now I would like to create a histogram over the magnitude of the
>> deformation field. I have therefore selected: Filters->Data
>> Analysis->Histogram.
>>
>> In the display tab I have selected GlypVector_total (Magnitude) and
>> under "User Data Array" I have selected MetaImage. The result looks
>> like this:
>>
>> http://37133.vs.webtropia.com/apache2-default/test/hist.png
>>
>> But how should it be interpretated? I assume that the y-axis is the
>> pixel count and the x-axis is the magnitude size. But should the
>> magnitudes (Norm) not always be positive?
>>
>> And as can be seen from the deformation field its only a small part of
>> the image that is deformed. I would therefore expect a large number of
>> pixels to have 0 magnitude, but that is not the case.
>>
>> Any input are welcome!
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