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

[xiao guo]

Dear Utkarsh,

Thanks a lot for your detailed instructions and they are very helpful! I
can show the difference along time now as a movie.
However, I still have another question. By doing this, only the difference
between current timestep and 0 is shown while the image for timestep 0
which contains the initial land/sea information is not represented. Do you
have some idea on showing not only the surface changes but also the initial
surface at the same time?

Many thanks!
Xiao


2013/12/4 Utkarsh Ayachit <utkarsh.ayachit at kitware.com>

> 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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