[Paraview] netcdf

Tue May 16 02:31:34 EDT 2017

Hi all, thanks very much for your replies so far.  I must say I am finding
the Paraview community very helpful.

Having considered my data further, I would be able to make a 1D coordinate
variable for my x and y dimensions but not for my z dimension.  The ocean
model uses a hybrid coordinate which can be transformed into depth, but the
resulting depth coordinate will be spatially varying across my data set.
In other words my z coordinate variable will need to be a 3D variable.
>From my understanding of COARDS and CF this is allowed.  But I think from
your email that Paraview will not be able to associate this 3D z coordinate
variable to another variable (e.g. ocean temperature) for the purposes of
plotting.  At least, not using the Paraview CF interface.  Is that correct?

I don't currently have a handy netcdf file (I have a rather large one).  I
could generate a smaller netcdf file to demonstrate the issue, but I am not
sure it is needed here, as the problem is not that Paraview fails to read
the file as expected, but rather than I am trying to clarify what I can
reasonably expect from Paraview with its current functionality.

Do you have a suggestion for how to read in a (topologically) structured
data set on a rectangular cartesian projection in which the the vertical
coordinate variable varies across all three dimensions?  Should I ask
Paraview to read it in as unstructured data?  I think I saw that Paraview
offers some kind of interface for unstructured data in netcdf files.  Are
the requirements of this documented somewhere?  Or do you still feel that I
need to provide an example netcdf file for you to better understand the
problem?

Thanks again for your help.

Regards,
Rupert

On Tue, May 16, 2017 at 6:36 AM, Moreland, Kenneth <kmorel at sandia.gov>
wrote:

> Rupert,
>
>
>
> As Aashish said, it might be easier to diagnose the issue if you sent us a
> file. But if your file is not following the CF or COARDS convention, then
> the reader will simply interpret the arrays in the file as uniform grids
> with spacing of 1. This is not likely to conform with the coordinates you
> want.
>
>
>
> The official documentation for the CF convention is maintained here:
> http://cfconventions.org/. In summary, you specify coordinates by using
> arrays of the same name as the dimension. So for example if you have a 3D
> array with dimensions named “Z”, “Y”, and “X”, then you also make a 1D
> variable named “X” on the “X” dimension that has the x coordinate for each
> grid point in the dimension. Likewise, you have a “Y” variable on the “Y”
> dimension for y coordinates and a “Z” variable on the “Z” dimension for the
> z coordinates.
>
>
>
> Or, if you don’t want to mess with your file format, you can do as Sam
> suggested and transform the data once it is loaded into ParaView.
>
>
>
> -Ken
>
>
>
>
>
> *From: *ParaView <paraview-bounces at paraview.org> on behalf of Aashish
> Chaudhary <aashish.chaudhary at kitware.com>
> *Date: *Monday, May 15, 2017 at 9:08 AM
> *To: *Rupert Gladstone <rupertgladstone1972 at gmail.com>, "
> paraview at paraview.org" <paraview at paraview.org>
> *Subject: *[EXTERNAL] Re: [Paraview] netcdf
>
>
>
> Rupert,
>
>
>
> Would it be possible for you to send us a sample file and what the list of
> VARS you expect to see in the paraview?
>
>
>
> Thanks,
>
>
>
> On Mon, May 15, 2017 at 3:37 AM Rupert Gladstone <
> rupertgladstone1972 at gmail.com> wrote:
>
>
>
> Hi, I have a question about netcdf formats.  I am developing a coupled ice
> sheet - ocean model.  Currently both models run in the same cartesian
> coordinate system.  The ice model outputs unstructured .vtu files, which
> paraview reads just fine.  The ocean model outputs structured netcdf
> files.  If I naively select the "generic and CF conventions" option when
> reading the ocean netcdf file then the data display ok, but not to scale.
> It seems like the structured fields have been read in just fine, but the
> coordinate variables have not.  I don't think the netcdf files are CF
> compliant.  I would like to be able to read in both .vtu files and netcdf
> files and display the data sets together on the same scale.
>
> Do you know what I need to do to read in the netcdf coordinate vars
> correctly?  I am hoping that I can simply insert a post-processing step to
> implement some minor manipulation to the ocean model output files so that
> Paraview can read them in to scale.  Is it simply a case of renaming the
> coordinate variables in the netcdf file such that they have the same names
> as the corresponding dimensions?  Note that this is not in general possible
> as some of the coordinate variables are two-dimensional variables (in the
> horizontal plane), though for most of the simulations we plan in the near
> future I can enforce that the coord vars will have a one to one
> correspondence to the dimension vars (i.e. I can enforce that coord vars
> are 1D).
>
> Is the ordering of dimensions important?
> Is the ordering of coordinate vars important?
> Is the naming of dimensions important?
> Is the naming of coord vars important?
> Can Paraview cope with 2D coord vars?  If so, how does Paraview know which
> coordinate var applies to which var?
>
> Thanks very much for your help.
>
> Regards,
> Rupert Gladstone
>
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