[Paraview] netCDF reader

[Moreland, Kenneth]

The netCDF reader in ParaView implements the COARDS convention, which is a subset of the CF convention.  To the best of my knowledge, both conventions define the spherical coordinates in the same way.  So if you have a netCDF file containing the CF convention for latitude and longitude, then the ParaView netCDF reader should understand that.

That said, I see that the netCDF reader will only actually create spherical coordinates for 3D grids.  I am not sure I remember the logic behind that, but I think it was that in general it is usually better to visualize a map surface as a 2D projection to prevent occlusion and that it is ambiguous what the height of the surface should be.  That said, it is easy to implement spherical coordinates to 2D grids.  I just checked in a change that creates a sphere at radius 1.

The idea of the netCDF reader outputting a vtkPolyData is unworkable.  Many netCDF files contain 3D grids, and vtkPolyData is incapable of representing those.  It could always output a vtkUnstructuredGrid, but this is a highly inefficient format for storing the structured arrays stored in netCDF COARDS files.  It is conceivable that the netCDF reader could always output a vtkStructuredGrid.  But that means that non-COARDS files are forced to also output vtkStructuredGrid and they loose the features for using vtkImageData.  I know there are issues with the VTK/ParaView pipeline when you change the output of the reader when you change the dimensions.  But there are also similar problems when you change the extent and dimensionality anyway, so I don't know how much help such a change would make.

-Ken


On 1/12/10 5:52 PM, "Brockmann Patrick" <Patrick.Brockmann at cea.fr> wrote:

Hi all,

Testing the netCDF reader with "spherical coordinates" set, I get
a vtkStructured Grid incomplete. There is no circular topology.
I was expecting a complete sphere where points from first column would be
connected to points from last column in the vtkStructuredGrid created.

Is there a way to do this from an existing filter or from
the python programmable filter ?
Or better could the netCDF reader be corrected
(VTK/IO/vtkNetCDFCOARDSReader.cxx) ?

By the past, I have installed and used the external plugin CSCSnetCDF
reader
from John Biddiscombe of the Swiss National Supercomputing Centre.
I was quite happy with it.
Today, I discover that paraview binairies are distributed with the
netCDFCOARDS reader
with some features I don't like. For example, that fact that the vtk
structure created
are different following the netCDF grid topology (regular spacing or
not, spherical coordinates or not).

I think it would be attractive for all the General Circulation Model
(GCM)/ /community
to provide a netCDF reader, closer to the CF (Climate and Forecast
netCDF convention) widely adopted.
This reader would create for example a same vtkPolydata structure
whatever the netCDF grid read
as in the vtk application described from
http://www.prism.enes.org/Publications/Reports/Report19.pdf

Is there any interest to develop this netCDFCF reader among offcial dev
team ?

Thanks
Patrick
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   ****      Kenneth Moreland
    ***      Sandia National Laboratories
***********
*** *** ***  email: kmorel at sandia.gov
**  ***  **  phone: (505) 844-8919
    ***      web:   http://www.cs.unm.edu/~kmorel

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