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Reading unstructured ICON NetCDF data

This page will guide you through the very first steps of reading and visualizing unstructured ICON NetCDF data files using ParaView on Mistral.

ParaView is a great choice for working with original grid ICON data or resampled lon/lat NetCDF data. To load ICON data, just select open file in ParaView, select the ICON NetCDF file, and choose from the NetCDF selector list CDI netCDF Reader (ICON):

netCDF Selector

Figure 1: Selecting the correct netCDF file type.

For regular lon/lat data or curvilinear MPI-OM ocean data, you would select NetCDF Files Generic and CF Conventions instead.

The plugin to load the ICON data has several options to chose from. Figure 2 shows a closeup of the plugin. The options are (in descending order from the top):

Dimensions: If the data contains data with different dimensions, for instance 2D and 3D, or 2D sampled at different height levels, the respective data can be selected here.

Point/Cell/Domain Array Status: These fields list the available variables to chose from. If your specific variable is not visible, check if the dimensions are correct (step above).

Project Lat/Lon: If enabled, the data will be displayed in lon/lat, i.e. equidistant cylindrical projection, compare with Figure 3.

Project Cassini: If enabled, the data will be displayed in Cassini (rotated lon/lat) projection. If neither Lon/Lat nor Cassini is selected, the data will be displayed using a spherical projection.

Use Topography (wet_c): This is only available for ocean data, in which, if enabled, the wet_c mask will be used to stencil out the land mass, compare with Figure 3.

Use Land/Sea for Masking: If the switch is enabled the above step will be inverted, and only the land and bathymetry data will be shown.

Invert Z-Axis: This function inverts the ordering of the vertical layer (z-axis).

Show 3D Surface: If 3D variables are available, This function allows to load and visualize the entire 3D variable, compare with Figure 3.

Read/Output Double Precision: Although single precision is fully sufficient for data visualization, sometimes it is necessary to load and visualize the data using double precision, e.g. for visualizing very tiny differences.

3D Surface Thickness: This is an additional parameter for the 3D data and allows to scale the thickness of the vertical layers. Their varying thickness (for instance in the ocean) is already considered, compare with Figure 3.

Vertical Level: The 3D data can also be visualized slice by slice with the vertical level set by this slider.

 CDI netCDF Reader (ICON)

Figure 2: Options of the ParaView ICON Reader Plugin.

After clicking Apply, the data will be loaded and the grid reconstructed. The variables loaded can then be selected for visualization from the ParaView main menu bar. If one or more parameters need to be changed, just make the modifications and click on the green Apply button again. Figure 3 shows a simple ocean simulation data set in which all point and cell variables have been loaded. Additional options that have been set are Lon/Lat Projection, Use Topography (wet_c), and Show 3D Surface. Within ParaView, the variable t_acc (i.e. ocean water temperature) has been chosen for display.

ParaView with ICON Ocean Data

Figure 3: ParaView with ICON Ocean Data.

Similar procedures apply for all other data sets, such as the ones from HD(CP)². Our old ParaView tutorial, which explains several workflows that are still valid, can be found here. Although some aspects of the user interface and ParaView's functionality have changed, the vast majority of this tutorial should still be up to date. If you have any questions, please contact .