Nemobug2 - bug fixes for a certain set of NEMO output

CHANGELOG.md

@@ -14,12 +14,13 @@ of being developed elsewhere.
 -----
 
 
-### Version `3.5.X`, first released 2026-10-09
+### Version `3.5.X`, first released XXXXXX
 
 #### Version `3.5.1`, released 2026-??-??
 
 * Update code to prevent deprecation-related warnings
   (https://github.com/NCAS-CMS/cf-plot/issues/72)
+* Prevent striped artefacts on curvilinear longitude/latitude grids such as NEMO.
 
 #### Version `3.5.0`, released 2026-10-09
 

cfplot/blockfill.py

@@ -108,9 +108,11 @@ def _bfill(
                 colarr[pts] = np.size(levels) - 2
 
     if isinstance(field, np.ma.MaskedArray):
-        pts = np.ma.where(field.mask)
-        if np.size(pts) > 0:
-            colarr[pts] = -1
+        # np.ma.where on a scalar False mask raises on newer NumPy.
+        # Use a normalized boolean mask array instead.
+        mask = np.ma.getmaskarray(field)
+        if np.any(mask):
+            colarr[mask] = -1
 
     norm = matplotlib.colors.BoundaryNorm(levels, cmap.N)
 

cfplot/contour.py

@@ -682,7 +682,7 @@ def render_filled(
         runtime.image = runtime.mymap.contourf(
             lons,
             lats,
-            self.data.field * self.data.fmult,
+            _mask_curvilinear_contour_seams(self.data) * self.data.fmult,
             self.data.levels,
             extend=scale.levels_extend,
             cmap=cmap,
@@ -792,10 +792,11 @@ def render_lines(
 
         runtime = plotvars.runtime
         dec = plotvars.decoration
+        field = _mask_curvilinear_contour_seams(self.data) * self.data.fmult
         cs = runtime.mymap.contour(
             self.data.x,
             self.data.y,
-            self.data.field * self.data.fmult,
+            field,
             self.data.levels,
             colors=colors,
             linewidths=linewidths,
@@ -825,7 +826,7 @@ def render_lines(
             cs0 = runtime.mymap.contour(
                 self.data.x,
                 self.data.y,
-                self.data.field * self.data.fmult,
+                field,
                 [-1e-32, 0],
                 colors=colors,
                 linewidths=zero_thick,
@@ -1697,6 +1698,70 @@ def _window_irregular_map_data(
     return field_irregular, lons_irregular, lats_irregular
 
 
+def _is_curvilinear_map_grid(data: ContourData) -> bool:
+    """Return True for map plots using 2D lon/lat coordinates.
+
+    Curvilinear grids (for example NEMO/ORCA ocean meshes) are prone to
+    severe contourf/contour artefacts. These are better rendered through
+    blockfill/pcolormesh.
+    """
+    if data.ptype != 1 or data.x is None or data.y is None:
+        return False
+    if np.ndim(data.field) != 2:
+        return False
+    return np.ndim(data.x) == 2 and np.ndim(data.y) == 2
+
+
+def _mask_curvilinear_contour_seams(data: ContourData) -> np.ndarray:
+    """Exclude vertices adjoining longitude jumps from structured contours."""
+    if not _is_curvilinear_map_grid(data):
+        return data.field
+
+    mask = np.ma.getmaskarray(data.field).copy()
+    for axis in (0, 1):
+        jumps = np.abs(np.diff(data.x, axis=axis)) > 180.0
+        before = [slice(None), slice(None)]
+        after = before.copy()
+        before[axis] = slice(None, -1)
+        after[axis] = slice(1, None)
+        # Mask both ends so corner masking cannot retain a seam-crossing
+        # triangle and interpolate a contour across the whole map.
+        mask[tuple(before)] |= jumps
+        mask[tuple(after)] |= jumps
+
+    return np.ma.array(data.field, mask=mask)
+
+
+def _resolve_curvilinear_render_defaults(
+    *,
+    data: ContourData,
+    kwargs: dict[str, Any],
+    fill: bool,
+    lines: bool,
+    blockfill: bool,
+    blockfill_fast: bool | None,
+) -> tuple[bool, bool, bool, bool | None]:
+    """Adjust renderer defaults for curvilinear lon/lat map grids.
+
+    Returns the possibly updated (fill, lines, blockfill, blockfill_fast)
+    tuple.
+    """
+    if not _is_curvilinear_map_grid(data):
+        return fill, lines, blockfill, blockfill_fast
+
+    # Use robust defaults for 2D map grids unless the caller explicitly
+    # requested alternative behavior.
+    if "blockfill" not in kwargs:
+        blockfill = True
+        fill = False
+    if blockfill and blockfill_fast is None:
+        blockfill_fast = True
+    if "lines" not in kwargs:
+        lines = False
+
+    return fill, lines, blockfill, blockfill_fast
+
+
 def _render_with_new_xy(
     f: Any, x: Any, y: Any, kwargs: dict[str, Any]
 ) -> bool:
@@ -1776,6 +1841,7 @@ def _render_with_new_xy(
     fill = kwargs.get("fill", global_fill)
     lines = kwargs.get("lines", global_lines)
     blockfill = kwargs.get("blockfill", global_blockfill)
+    blockfill_fast = kwargs.get("blockfill_fast", None)
     line_labels = kwargs.get("line_labels", True)
     zero_thick = kwargs.get("zero_thick", False)
     colors = kwargs.get("colors", "k")
@@ -1787,6 +1853,17 @@ def _render_with_new_xy(
     if blockfill:
         fill = False
 
+    fill, lines, blockfill, blockfill_fast = (
+        _resolve_curvilinear_render_defaults(
+            data=data,
+            kwargs=kwargs,
+            fill=fill,
+            lines=lines,
+            blockfill=blockfill,
+            blockfill_fast=blockfill_fast,
+        )
+    )
+
     colorbar = kwargs.get("colorbar", True)
     if not fill and not blockfill:
         colorbar = False
@@ -2171,7 +2248,7 @@ def _render_with_new_xy(
         )
     if blockfill:
         renderer.render_blockfill(
-            fast=kwargs.get("blockfill_fast", None), alpha=alpha, zorder=zorder
+            fast=blockfill_fast, alpha=alpha, zorder=zorder
         )
     if lines:
         renderer.render_lines(
@@ -2350,7 +2427,11 @@ def con(f=None, x=None, y=None, **kwargs):
     |                       6 = rotated pole
     | negative_linestyle='solid' - set to one of 'solid', 'dashed'
     | zero_thick=False - add a thick zero contour line. Set to 3 for example.
-    | blockfill=False - set to True for a blockfill plot
+    | blockfill=False - set to True for a blockfill plot. For 2D lon/lat
+    |                  grids, defaults to fast blockfill without lines.
+    |                  Explicit False selects contours; vertices adjoining
+    |                  longitude wrap jumps are excluded to avoid stripes,
+    |                  leaving a narrow gap at the seam.
     | colorbar_title=colbar_title - title for the colour bar
     | colorbar=True - add a colour bar if a filled contour plot
     | colorbar_label_skip=None - skip colour bar labels. Set to 2 to skip

docs/source/examples/example_1.rst

@@ -14,4 +14,4 @@ Example 1: Basic contour plot in default projection
    cfp.con(f.subspace(time=15))
 
 
-.. figure:: /../../tests/reference-example-images/ref_fig_1.png
+.. figure:: /../../tests/v350-controlled-env-ref-images/ref_fig_1.png

docs/source/examples/example_10.rst

@@ -14,4 +14,4 @@ Example 10: Latitude-time Hovmöller plot
    cfp.con(f.subspace(longitude=0), lines=0)
 
 
-.. figure:: /../../tests/reference-example-images/ref_fig_10.png
+.. figure:: /../../tests/v350-controlled-env-ref-images/ref_fig_10.png

docs/source/examples/example_11.rst

@@ -18,4 +18,4 @@ Example 11: Latitude-time subset view Hovmöller plot
    cfp.con(f.subspace(longitude=0), lines=0)
 
 
-.. figure:: /../../tests/reference-example-images/ref_fig_11.png
+.. figure:: /../../tests/v350-controlled-env-ref-images/ref_fig_11.png

docs/source/examples/example_12.rst

@@ -14,4 +14,4 @@ Example 12: Longitude-time Hovmöller plot
    cfp.con(f.subspace(latitude=0), lines=0)
 
 
-.. figure:: /../../tests/reference-example-images/ref_fig_12.png
+.. figure:: /../../tests/v350-controlled-env-ref-images/ref_fig_12.png

docs/source/examples/example_13.rst

@@ -18,4 +18,4 @@ Example 13: Basic vector plot
 
    cfp.vect(u=u, v=v, key_length=10, scale=100, stride=5)
 
-.. figure:: /../../tests/reference-example-images/ref_fig_13.png
+.. figure:: /../../tests/v350-controlled-env-ref-images/ref_fig_13.png

docs/source/examples/example_14.rst

@@ -26,4 +26,4 @@ Example 14: Vector plot overlaid on a contour map
    cfp.gclose()
 
 
-.. figure:: /../../tests/reference-example-images/ref_fig_14.png
+.. figure:: /../../tests/v350-controlled-env-ref-images/ref_fig_14.png

docs/source/examples/example_15.rst

@@ -37,4 +37,4 @@ Example 15: Polar projection vector plot
    cfp.gclose()
 
 
-.. figure:: /../../tests/reference-example-images/ref_fig_15.png
+.. figure:: /../../tests/v350-controlled-env-ref-images/ref_fig_15.png

docs/source/examples/example_16a.rst

@@ -29,4 +29,4 @@ Example 16a: Zonal vector plot
    )
 
 
-.. figure:: /../../tests/reference-example-images/ref_fig_16a.png
+.. figure:: /../../tests/v350-controlled-env-ref-images/ref_fig_16a.png

docs/source/examples/example_16b.rst

@@ -21,4 +21,4 @@ Example 16b: Basic stream plot
    cfp.stream(u=u, v=v, density=2)
 
 
-.. figure:: /../../tests/reference-example-images/ref_fig_16b.png
+.. figure:: /../../tests/v350-controlled-env-ref-images/ref_fig_16b.png

docs/source/examples/example_16c.rst

@@ -34,4 +34,4 @@ Example 16c: Stream plot in a colour scale
    )
    cfp.gclose()
 
-.. figure:: /../../tests/reference-example-images/ref_fig_16c.png
+.. figure:: /../../tests/v350-controlled-env-ref-images/ref_fig_16c.png

docs/source/examples/example_17.rst

@@ -22,4 +22,4 @@ Example 17: Basic stipple plot
    cfp.gclose()
 
 
-.. figure:: /../../tests/reference-example-images/ref_fig_17.png
+.. figure:: /../../tests/v350-controlled-env-ref-images/ref_fig_17.png

docs/source/examples/example_18.rst

@@ -19,4 +19,4 @@ Example 18: Polar stipple plot
    cfp.gclose()
 
 
-.. figure:: /../../tests/reference-example-images/ref_fig_18.png
+.. figure:: /../../tests/v350-controlled-env-ref-images/ref_fig_18.png

docs/source/examples/example_19a.rst

@@ -29,4 +29,4 @@ Example 19a: Multiple plots
    cfp.gclose()
 
 
-.. figure:: /../../tests/reference-example-images/ref_fig_19a.png
+.. figure:: /../../tests/v350-controlled-env-ref-images/ref_fig_19a.png

docs/source/examples/example_19b.rst

@@ -25,4 +25,4 @@ Example 19b: Multiple plots with user-specified plot positions
    cfp.gclose()
 
 
-.. figure:: /../../tests/reference-example-images/ref_fig_19b.png
+.. figure:: /../../tests/v350-controlled-env-ref-images/ref_fig_19b.png

docs/source/examples/example_19c.rst

@@ -39,4 +39,4 @@ Example 19c: Accomodating more than one colour bar
    cfp.gclose()
 
 
-.. figure:: /../../tests/reference-example-images/ref_fig_19c.png
+.. figure:: /../../tests/v350-controlled-env-ref-images/ref_fig_19c.png

docs/source/examples/example_2.rst

@@ -13,4 +13,4 @@ Example 2: Basic blockfill plot in default projection
    cfp.con(f.subspace(time=15), blockfill=True, lines=False)
 
 
-.. figure:: /../../tests/reference-example-images/ref_fig_2.png
+.. figure:: /../../tests/v350-controlled-env-ref-images/ref_fig_2.png

docs/source/examples/example_20.rst

@@ -15,4 +15,4 @@ Example 20: Case where user-defined axis labels are required
    cfp.con(f.subspace[9])
 
 
-.. figure:: /../../tests/reference-example-images/ref_fig_20.png
+.. figure:: /../../tests/v350-controlled-env-ref-images/ref_fig_20.png

docs/source/examples/example_21a.rst

@@ -21,4 +21,4 @@ Example 21a: User-defined axes
    )
 
 
-.. figure:: /../../tests/reference-example-images/ref_fig_21a.png
+.. figure:: /../../tests/v350-controlled-env-ref-images/ref_fig_21a.png

docs/source/examples/example_21b.rst

@@ -14,4 +14,4 @@ Example 21b: Plot of rotated pole data
 
    cfp.con(f)
 
-.. figure:: /../../tests/reference-example-images/ref_fig_21b.png
+.. figure:: /../../tests/v350-controlled-env-ref-images/ref_fig_21b.png

docs/source/examples/example_22.rst

@@ -16,4 +16,4 @@ Example 22: Plot of rotated pole data on its native grid
    cfp.con(f)
 
 
-.. figure:: /../../tests/reference-example-images/ref_fig_22.png
+.. figure:: /../../tests/v350-controlled-env-ref-images/ref_fig_22.png

docs/source/examples/example_23a.rst

@@ -30,4 +30,4 @@ Example 23a: Rotated pole plot from data which is not CF Compliant
    cfp.gclose()
 
 
-.. figure:: /../../tests/reference-example-images/ref_fig_23a.png
+.. figure:: /../../tests/v350-controlled-env-ref-images/ref_fig_23a.png

docs/source/examples/example_23b.rst

@@ -23,4 +23,4 @@ Example 23b: Overlaying vectors over a rotated pole data plot
    cfp.gclose()
 
 
-.. figure:: /../../tests/reference-example-images/ref_fig_23b.png
+.. figure:: /../../tests/v350-controlled-env-ref-images/ref_fig_23b.png

docs/source/examples/example_24a.rst

@@ -28,4 +28,4 @@ Example 24a: UGRID blockfill plot with LFRic cubed sphere mesh output
    )
 
 
-.. figure:: /../../tests/reference-example-images/ref_fig_24a.png
+.. figure:: /../../tests/v350-controlled-env-ref-images/ref_fig_24a.png

docs/source/examples/example_24b.rst

@@ -30,4 +30,4 @@ Example 24b: UGRID plot in the polar stereographic projection view
    )
 
 
-.. figure:: /../../tests/reference-example-images/ref_fig_24b.png
+.. figure:: /../../tests/v350-controlled-env-ref-images/ref_fig_24b.png

docs/source/examples/example_24c.rst

@@ -17,4 +17,4 @@ Example 24c: UGRID contour plot with LFRic cubed sphere mesh output
    cfp.con(g, lines=False)
 
 
-.. figure:: /../../tests/reference-example-images/ref_fig_24c.png
+.. figure:: /../../tests/v350-controlled-env-ref-images/ref_fig_24c.png

docs/source/examples/example_25.rst

@@ -26,4 +26,4 @@ Example 25: UGRID contour plot with ORCA 2 output
    cfp.con(f=temp.array, x=lons.array, y=lats.array, ptype=1)
 
 
-.. figure:: /../../tests/reference-example-images/ref_fig_25.png
+.. figure:: /../../tests/v350-controlled-env-ref-images/ref_fig_25.png

docs/source/examples/example_26a.rst

@@ -29,4 +29,4 @@ Example 26a: Contour plot based on discrete feature values
    )
 
 
-.. figure:: /../../tests/reference-example-images/ref_fig_26a.png
+.. figure:: /../../tests/v350-controlled-env-ref-images/ref_fig_26a.png

docs/source/examples/example_26b.rst

@@ -43,4 +43,4 @@ Example 26b: Contour plot from discrete feature values with labelling
    cfp.gclose()
 
 
-.. figure:: /../../tests/reference-example-images/ref_fig_26b.png
+.. figure:: /../../tests/v350-controlled-env-ref-images/ref_fig_26b.png

docs/source/examples/example_27.rst

@@ -22,4 +22,4 @@ Example 27: Basic line plot
    cfp.gclose()
 
 
-.. figure:: /../../tests/reference-example-images/ref_fig_27.png
+.. figure:: /../../tests/v350-controlled-env-ref-images/ref_fig_27.png

docs/source/examples/example_28.rst

@@ -58,4 +58,4 @@ Example 28: Line plot with a legend
    cfp.gclose()
 
 
-.. figure:: /../../tests/reference-example-images/ref_fig_28.png
+.. figure:: /../../tests/v350-controlled-env-ref-images/ref_fig_28.png

docs/source/examples/example_29.rst

@@ -22,4 +22,4 @@ Example 29: Time series line plot
    )
 
 
-.. figure:: /../../tests/reference-example-images/ref_fig_29.png
+.. figure:: /../../tests/v350-controlled-env-ref-images/ref_fig_29.png

docs/source/examples/example_3.rst

@@ -17,4 +17,4 @@ Example 3: Contour plot with altered map limits and levels
    cfp.con(f.subspace(time=15))
 
 
-.. figure:: /../../tests/reference-example-images/ref_fig_3.png
+.. figure:: /../../tests/v350-controlled-env-ref-images/ref_fig_3.png

docs/source/examples/example_30.rst

@@ -31,4 +31,4 @@ Example 30: Line plot with two x axes
    cfp.gclose()
 
 
-.. figure:: /../../tests/reference-example-images/ref_fig_30.png
+.. figure:: /../../tests/v350-controlled-env-ref-images/ref_fig_30.png

docs/source/examples/example_31.rst

@@ -15,4 +15,4 @@ Example 31: UKCP projection
 
    cfp.con(f, lines=False)
 
-.. figure:: /../../tests/reference-example-images/ref_fig_31.png
+.. figure:: /../../tests/v350-controlled-env-ref-images/ref_fig_31.png

docs/source/examples/example_32.rst

@@ -23,4 +23,4 @@ Example 32: UKCP projection with blockfill
    )
 
 
-.. figure:: /../../tests/reference-example-images/ref_fig_32.png
+.. figure:: /../../tests/v350-controlled-env-ref-images/ref_fig_32.png

docs/source/examples/example_33.rst

@@ -20,4 +20,4 @@ Example 33: OSGB and EuroPP projections
    cfp.gclose()
 
 
-.. figure:: /../../tests/reference-example-images/ref_fig_33.png
+.. figure:: /../../tests/v350-controlled-env-ref-images/ref_fig_33.png