Rupert,

It has been multiple years since I really took a look at the CF convention, so 
I don’t remember the details of whether it supports varying coordinates across 
multiple dimensions or whether the ParaView reader supports that. If the 
ParaView reader is missing some corner of the CF convention, let us know and we 
can work on that.

In any case, you can displace a 2D or 3D image by a height value that is stored 
in a field by simply running the “Warp by Scalar” filter.

-Ken


From: Rupert Gladstone <rupertgladstone1...@gmail.com>
Date: Tuesday, May 16, 2017 at 12:31 AM
To: "Moreland, Kenneth" <kmo...@sandia.gov>
Cc: Aashish Chaudhary <aashish.chaudh...@kitware.com>, "paraview@paraview.org" 
<paraview@paraview.org>
Subject: [EXTERNAL] Re: [Paraview] netcdf

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 
<kmo...@sandia.gov<mailto:kmo...@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-boun...@paraview.org<mailto:paraview-boun...@paraview.org>> on behalf 
of Aashish Chaudhary 
<aashish.chaudh...@kitware.com<mailto:aashish.chaudh...@kitware.com>>
Date: Monday, May 15, 2017 at 9:08 AM
To: Rupert Gladstone 
<rupertgladstone1...@gmail.com<mailto:rupertgladstone1...@gmail.com>>, 
"paraview@paraview.org<mailto:paraview@paraview.org>" 
<paraview@paraview.org<mailto:paraview@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 
<rupertgladstone1...@gmail.com<mailto:rupertgladstone1...@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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