Replicate percentile collapse functionality.

This commit also addresses many of the review comments
though the expansion / rewriting of the unit tests will
be undertaken separately.

The BasicThreshold plugin is also renamed to Threshold.

doc/source/Code-Style-Guide.rst

@@ -342,7 +342,7 @@ Plugins (classes) should be an example of a non-trivial algorithm or set
 of algorithms for a particular purpose. They should be set up via the
 ``__init__`` method and then invoked on a particular iris Cube ``cube``
 using a ``process`` method - e.g. using ``process(cube)``. See
-e.g. `BasicThreshold <https://github.com/metoppv/improver/blob/master/lib/improver/threshold.py>`_
+e.g. `Threshold <https://github.com/metoppv/improver/blob/master/lib/improver/threshold.py>`_
 class. In some limited cases an iris ``CubeList`` may be preferable.
 Avoid writing code that can do both. Class names use
 `PascalCase <https://en.wikipedia.org/wiki/PascalCase>`_ whilst

improver/cli/threshold.py

@@ -45,7 +45,7 @@ def process(
     threshold_units: str = None,
     comparison_operator=">",
     fuzzy_factor: float = None,
-    collapse_realizations: bool = False,
+    collapse_coord: str = None,
     vicinity: cli.comma_separated_list = None,
     fill_masked: float = None,
 ):
@@ -96,9 +96,14 @@ def process(
             indicating a narrower fuzzy factor region / sharper threshold.
             A fuzzy factor cannot be used with a zero threshold or a
             threshold_config file.
-        collapse_realizations (bool):
-            If set, the realization coordinate is collapsed to calculate an
-            ensemble average threshold exceedance value.
+        collapse_coord (str):
+            An optional ability to set which coordinate we want to collapse
+            over. The only supported options are "realization" or "percentile".
+            If "percentile" is requested, the percentile coordinate will be
+            rebadged as a realization coordinate prior to collapse. The percentile
+            coordinate needs to be evenly spaced around the 50th percentile
+            to allow successful conversion from percentiles to realizations and
+            subsequent collapsing over the realization coordinate.
         vicinity (list of float / int):
             List of distances in metres used to define the vicinities within
             which to search for an occurrence. Each vicinity provided will
@@ -115,13 +120,8 @@ def process(
         ValueError: If threshold_config and threshold_values are both set
         ValueError: If threshold_config is used for fuzzy thresholding
         ValueError: Cannot apply land-mask cube without in-vicinity processing.
-        ValueError: Can only collapse over a realization coordinate or a percentile
-            coordinate that has been rebadged as a realization coordinate.
     """
-    from improver.ensemble_copula_coupling.ensemble_copula_coupling import (
-        RebadgePercentilesAsRealizations,
-    )
-    from improver.threshold import BasicThreshold
+    from improver.threshold import Threshold
 
     if threshold_config and threshold_values:
         raise ValueError(
@@ -133,13 +133,13 @@ def process(
     if fill_masked is not None:
         fill_masked = float(fill_masked)
 
-    return BasicThreshold(
+    return Threshold(
         threshold_values=threshold_values,
         threshold_config=threshold_config,
         fuzzy_factor=fuzzy_factor,
         threshold_units=threshold_units,
         comparison_operator=comparison_operator,
-        collapse_realizations=collapse_realizations,
+        collapse_coord=collapse_coord,
         vicinity=vicinity,
         fill_masked=fill_masked,
     )(cube, land_sea_mask)

improver/precipitation_type/shower_condition_probability.py

@@ -44,7 +44,7 @@
     create_new_diagnostic_cube,
     generate_mandatory_attributes,
 )
-from improver.threshold import BasicThreshold
+from improver.threshold import Threshold
 from improver.utilities.cube_manipulation import collapse_realizations
 
 from .utilities import make_shower_condition_cube
@@ -171,10 +171,10 @@ def process(self, cubes: CubeList) -> Cube:
         cloud, convection = self._extract_inputs(cubes)
 
         # Threshold cubes
-        cloud_thresholded = BasicThreshold(
+        cloud_thresholded = Threshold(
             self.cloud_threshold, comparison_operator="<="
         ).process(cloud)
-        convection_thresholded = BasicThreshold(self.convection_threshold).process(
+        convection_thresholded = Threshold(self.convection_threshold).process(
             convection
         )
 

improver/regrid/landsea.py

@@ -45,7 +45,7 @@
 from improver.metadata.constants.attributes import MANDATORY_ATTRIBUTE_DEFAULTS
 from improver.metadata.constants.mo_attributes import MOSG_GRID_ATTRIBUTES
 from improver.regrid.landsea2 import RegridWithLandSeaMask
-from improver.threshold import BasicThreshold
+from improver.threshold import Threshold
 from improver.utilities.cube_checker import spatial_coords_match
 from improver.utilities.spatial import OccurrenceWithinVicinity
 
@@ -288,9 +288,9 @@ def _get_matches(
         # Identify nearby points on regridded input_land that match the
         # selector_value
         if selector_val > 0.5:
-            thresholder = BasicThreshold(0.5)
+            thresholder = Threshold(0.5)
         else:
-            thresholder = BasicThreshold(0.5, comparison_operator="<=")
+            thresholder = Threshold(0.5, comparison_operator="<=")
         in_vicinity = self.vicinity(thresholder(self.input_land))
 
         # Identify those points sourced from the opposite mask that are