New docs multi-layer plotting example

docs/source/reference/gallery/examples/spatial/plot_spatial_multi.py

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+"""
+Overlay plots
+=============
+
+Generate spatial map with overlays of multiple 2D fields.
+
+.. admonition:: References
+
+   General functionality is provided using the following :doc:`CSET recipes </usage/operator-recipes>`:
+
+   * ``multi_surface_spatial_plot_sequence.yaml`` for 3-layer plots (base layer, masked overlay layer, contour layer)
+   * ``multi_overlay_spatial_plot_sequence.yaml`` for base-layer with masked pcolormesh overlay
+   * ``multi_contour_spatial_plot_sequence.yaml`` for base-layer with contour overlay
+
+   The following CSET operators are used:
+
+   * :py:mod:`CSET.operators.read.read_cubes`
+   * :py:mod:`CSET.operators.filters.generate_mask`
+   * :py:mod:`CSET.operators.filters.apply_mask`
+   * :py:mod:`CSET.operators.plot.spatial_multi_pcolormesh_plot`.
+
+Using *cset bake* on the command line
+-------------------------------------
+
+* Access recipe file using ``cset cookbook``.
+* Set required recipe inputs on command line.
+
+Example to generate 3-layer full-domain spatial maps of ``temperature_at_screen_level``, with overlay of ``microphysical_surface_rainfall_rate`` masked to show only values greater than or equal to 0.05, and overlay of contours of ``air_pressure_at_sea_level`` for all output times::
+
+    cset cookbook multi_surface_spatial_plot_sequence.yaml
+    cset -v bake -i "/path/to/input/data" -o "./output_path" \\
+                 -r multi_surface_spatial_plot_sequence.yaml \\
+                 --VARNAME_BASE="temperature_at_screen_level" \\
+                 --VARNAME_OVER="surface_microphysical_rainfall_rate" \\
+                 --OVERLAY_MASK_CONDITION="ge" \\
+                 --OVERLAY_MASK_VALUE="0.05" \\
+                 --VARNAME_CONTOUR="air_pressure_at_mean_sea_level" \\
+                 --MODEL_NAME="my_model_label" \\
+                 --METHOD="SEQ" \\
+                 --SUBAREA_TYPE='None' --SUBAREA_EXTENT='None' --SUBAREA_NAME='None'
+
+Similar examples can be generated using recipe ``multi_overlay_spatial_plot_sequence.yaml`` for outputs with only ``VARNAME_BASE`` and ``VARNAME_OVER`` shown.
+
+Alternatively, examples can be generated using recipe ``multi_contour_spatial_plot_sequence.yaml`` for outputs with only ``VARNAME_BASE`` and ``VARNAME_CONTOUR`` shown.
+
+
+Configuring the *cset_workflow*
+-------------------------------
+
+* Update workflow configuration settings via ``rose edit`` GUI or in ``rose-suite.conf`` file.
+* Complete ``General setup options`` and ``Cycling and Model options`` details - see :doc:`/usage/workflow-configure`.
+* Set required configuration options on ``Diagnostics / Multi-variable plots`` panel
+* A list of different variables can be specified as python lists to generate multiple different output plot combinations using the same workflow run.
+* If all variables are set, 3-layer overlay plots are generated. If either ``OVERLAY`` or ``CONTOUR`` variables are not set, the relevant 2-layer outputs are generated.
+::
+
+    SPATIAL_MULTI_VARIABLE = True
+    MULTI_BASE_FIELDS = ["temperature_at_screen_level", ...]
+    MULTI_OVERLAY_FIELDS = ["surface_microphysical_rainfall_rate", ...]
+    MULTI_OVERLAY_MASK_CONDITIONS = ["ge", ...]
+    MULTI_OVERLAY_MASK_VALUES = ["0.05", ...]
+    MULTI_CONTOUR_FIELDS = ["air_pressure_at_mean_sea_level", ...]
+    SPATIAL_MULTI_FIELD_METHOD = ""
+
+
+Example python code
+-------------------
+"""
+
+from CSET import sample_data_path
+from CSET.operators import plot, read
+
+# Set path to input data
+filename = sample_data_path("air_temperature_global.nc")
+
+# Read selected variable(s) of interest
+# Select sub-region to better illustrate output plot
+cube = read.read_cube(
+    filename,
+    ["temperature_at_screen_level"],
+    subarea_type="realworld",
+    subarea_extent=[-40.0, 40.0, -120.0, -55.0],
+)
+
+# Plot single time using spatial_multi_pcolormesh_plot
+# Here only contours of cube are shown for simplest illustration
+# See operator documentation to generate more complex multi-layer examples
+plot.spatial_multi_pcolormesh_plot(cube, contour_cube=cube)