fix: protect against tiny floating point deltas

CHANGELOG.md

@@ -14,6 +14,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 ### Fixed
 
 - Don't produce meaningless splits when one corner of an input polygon is on the antimeridian ([#49](https://github.com/gadomski/antimeridian/pull/49))
+- Correct tiny floating point deltas on the antimeridian ([#52](https://github.com/gadomski/antimeridian/pull/52))
 
 ## [0.3.0] - 2023-06-29
 

README.md

@@ -9,7 +9,7 @@
 
 Fix shapes that cross the antimeridian.
 See [the documentation](https://antimeridian.readthedocs.io) for information about the underlying algorithm.
-Depends on [shapely](https://shapely.readthedocs.io).
+Depends on [shapely](https://shapely.readthedocs.io) and [numpy](https://numpy.org/).
 
 Can fix:
 

pyproject.toml

@@ -14,7 +14,8 @@ classifiers = [
     "Development Status :: 4 - Beta",
 ]
 dependencies = [
-    "shapely>=2.0"
+    "numpy>=1.16",
+    "shapely>=2.0",
 ]
 
 [project.urls]

src/antimeridian/_implementation.py

@@ -12,6 +12,7 @@
 import warnings
 from typing import Any, Dict, List, Optional, Protocol, Tuple, Union, cast
 
+import numpy
 import shapely
 import shapely.geometry
 from shapely.geometry import (
@@ -426,8 +427,13 @@ def segment(coords: List[Point]) -> List[List[Point]]:
     segment = []
     segments = []
     for i, point in enumerate(coords):
-        # Ensure all longitudes are between -180 and 180
-        if point[0] != 180:
+        # Ensure all longitudes are between -180 and 180, and that tiny floating
+        # point differences are ignored.
+        if numpy.isclose(point[0], 180):
+            coords[i] = (180, point[1])
+        elif numpy.isclose(point[0], -180):
+            coords[i] = (-180, point[1])
+        else:
             coords[i] = (((point[0] + 180) % 360) - 180, point[1])
     for start, end in zip(coords, coords[1:]):
         segment.append(start)

tests/data/input/almost-180.json

@@ -0,0 +1,27 @@
+{
+  "type": "Polygon",
+  "coordinates": [
+    [
+      [
+        -176.78115373,
+        -18.58572933
+      ],
+      [
+        -173.71026732,
+        -14.73835555
+      ],
+      [
+        -176.88248512,
+        -12.82925277
+      ],
+      [
+        179.99999999999997,
+        -15.7250416
+      ],
+      [
+        -176.78115373,
+        -18.58572933
+      ]
+    ]
+  ]
+}

tests/data/output/almost-180.json

@@ -0,0 +1,27 @@
+{
+  "type": "Polygon",
+  "coordinates": [
+    [
+      [
+        -180,
+        -15.7250416
+      ],
+      [
+        -176.78115373,
+        -18.58572933
+      ],
+      [
+        -173.71026732,
+        -14.73835555
+      ],
+      [
+        -176.88248512,
+        -12.82925277
+      ],
+      [
+        -180,
+        -15.7250416
+      ]
+    ]
+  ]
+}

tests/test_polygon.py

@@ -10,6 +10,7 @@
 @pytest.mark.parametrize(
     ("name"),
     [
+        "almost-180",
         "complex-split",
         "crossing-latitude",
         "extra-crossing",