a bit more on PV pre-processing

source/Paraview/Examples/PalMod_combined/index.rst

@@ -18,7 +18,7 @@ This example will show how to create an animation based on ocean, vegetation, so
 .. image:: combined-image.png
 
 
-In this example we assume a very basic level of familiarity with Paraview. If you feel lost in between, consider looking at :ref:`create-image-sea-surface-speeds`.
+In this example we assume a very basic level of familiarity with Paraview. If you feel lost in between, consider looking at :ref:`create-image-sea-surface-speeds`. This multi-variable visualization requires a substantial amount of :ref:`paraview-palmod-pre-processing`.
 
 * :ref:`vegetation-data`
 

source/Paraview/Examples/PalMod_combined/pre-processing.rst

+.. _paraview-palmod-pre-processing:
+
+Pre-Processing for a multi-variable image / animation
+============================================================
+
+* For general advice on the NetCDF CF reader see :ref:`netcdf-cf-reader`
+* All files need the same time axis. Different models will usually use different specifications, sending you straight to hell. One solution that works: resample all files to the same number of time steps, then use::
+
+    ncks -Av time MASTER_FILE FILE1
+    ncks -Av time MASTER_FILE FILE2
+    ...
+
+  to get all on the same time axis. If that causes trouble (e.g. because of float/double conversions), look into ``cdo -settaxis``.
+
+  .. warning::
+     The time axis must not contain negative values (don't ask how long it took to figure this out)
+
+
+* For extruding with topography it's best to have the topography in the same file as the data of interest. See :ref:`extrude-land-surface` for hints.
+
+* MPI-OM 2d data needs::
+
+    cdo -setzaxis,surface IN OUT
+
+  to get rid of the layer-dimension that does not have any content.

source/Paraview/Readers/cf-reader.rst

@@ -12,7 +12,9 @@ Issues:
 * The reader cannot display distorted grids in the plane (e.g. most ocean models)
 * The reader cannot handle a 2D field that has a depth axis (use ``cdo -setzaxis,surface INFILE OUTFILE`` or ``ncwa -a NAME_OF_DEPTH_DIMENSION INFILE OUTFILE`` to prepare files; affects a lot of MPI-OM output).
 * Ocean models tend to give positive values for depth. That requires a couple switches in the reader, see :ref:`load-nemo`.
+* For MPI-OM velocities, first use ``cdo -mrotuvb`` to get data to North/South East/West orientation, and interpolate u and v onto the cell centers.
 * Nemo grids cause weird hick-ups.
+* One file with many time steps tends to be a lot faster than many files with one timestep each.
 
 .. _open-with-cf-reader: