[Paraview] About visualizing vtk files in Paraview to show data changes maybe with two layers?

[Utkarsh Ayachit]

Xiao,

You can make ParaView compute a new data array that's the difference
between the values at 0 and the current timestep and then color with
that. To do that, do the following:

+ Open your snapshot000*.vtk file series as before.
+ Now, open just the  snapshoot0000.vtk file (the file for the first
time step) separately. In the file dialog, you can click on the "+"
icon next to the file group to expand the group and select a specific
file instead.
+ Next, select the filter series source as well as the
snapshoot0000.vtk source and create the Python calculator. Your
pipeline browser should like the one in the attached image.
+ Now for the Python calculator select Array Association as "Cell
Data" and setup an expression as follows to compare the quantities of
interest (as shown in the attached image).

    inputs[0].CellData["U"] - inputs[1].CellData["U"]

Now when you color by result, you'll be coloring by the difference in
the quantities  between timestep 0 and the current timestep.

Utkarsh

On Mon, Nov 25, 2013 at 2:47 PM, Utkarsh Ayachit
<utkarsh.ayachit at kitware.com> wrote:
> Xiao Guo,
>
> I am sure what you want could be done. Do you have a sample dataset so
> I can play with it figure out what would be easiest route?
>
> Utkarsh
>
> On Thu, Nov 21, 2013 at 1:19 PM, xiao guo <xiao.guo.math at gmail.com> wrote:
>> Hi all,
>>
>> I am trying to visualize some vtk files which are generally a series of
>> values of wave and sea level of some area. Now I can just save an animation
>> to show some movies of frame1,2,3,....
>> However, it is not clear for some regions that the values there are changed.
>> For example, when the wave goes to land, the value for the land increases
>> from saying 5m to 6m, so there is 1m flood however which is not easy to see
>> such small difference especially the change is even smaller saying 0.2 m..
>> What I am thinking is to 1) keep the first frame which is the initial value
>> for the area as one layer or background with some color scheme; then 2)
>> based on the background from 1), difference between the values at step i
>> (i=2,3,...) and the initial value (step 0, background) are shown with
>> another color scheme, so both the initial image for the area and the changes
>> afterwards can be shown clearly.
>>
>> But I am really not expert in such visualizing work or Paraview, so I come
>> here and ask for help. Anyone knows that if I can do such complicated work
>> in Paraview and how? Thank you all for attention!
>>
>> Cheers,
>> Xiao Guo
>>
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