From cc6689a5a8f13f253b060d9c93a4dc7d088d91f6 Mon Sep 17 00:00:00 2001
From: Mark Racette <markracette@gmail.com>
Date: Mon, 18 Sep 2023 19:53:47 -0500
Subject: [PATCH] Lines with a 180 degree angle between them should be
 considered parallel (`turf-boolean-parallel`) (#2475)

* Lines with a 180 degree angle between them are considered parallel

* Add simple verticals test

* Add failing test case for 3d lines

* Fix verticals 3d test
---
 packages/turf-boolean-parallel/index.ts       |  2 +-
 .../test/true/opposites.geojson               | 27 +++++++++++++++++++
 .../test/true/verticals.geojson               | 27 +++++++++++++++++++
 .../test/true/verticals3d.geojson             | 27 +++++++++++++++++++
 4 files changed, 82 insertions(+), 1 deletion(-)
 create mode 100644 packages/turf-boolean-parallel/test/true/opposites.geojson
 create mode 100644 packages/turf-boolean-parallel/test/true/verticals.geojson
 create mode 100644 packages/turf-boolean-parallel/test/true/verticals3d.geojson

diff --git a/packages/turf-boolean-parallel/index.ts b/packages/turf-boolean-parallel/index.ts
index 1c18d58305..5b055138dd 100644
--- a/packages/turf-boolean-parallel/index.ts
+++ b/packages/turf-boolean-parallel/index.ts
@@ -53,7 +53,7 @@ function booleanParallel(
 function isParallel(segment1: Position[], segment2: Position[]) {
   var slope1 = bearingToAzimuth(rhumbBearing(segment1[0], segment1[1]));
   var slope2 = bearingToAzimuth(rhumbBearing(segment2[0], segment2[1]));
-  return slope1 === slope2;
+  return slope1 === slope2 || (slope2 - slope1) % 180 === 0;
 }
 
 /**
diff --git a/packages/turf-boolean-parallel/test/true/opposites.geojson b/packages/turf-boolean-parallel/test/true/opposites.geojson
new file mode 100644
index 0000000000..7911a6359e
--- /dev/null
+++ b/packages/turf-boolean-parallel/test/true/opposites.geojson
@@ -0,0 +1,27 @@
+{
+  "type": "FeatureCollection",
+  "features": [
+    {
+      "type": "Feature",
+      "properties": {},
+      "geometry": {
+        "type": "LineString",
+        "coordinates": [
+          [0, 0],
+          [1, 0]
+        ]
+      }
+    },
+    {
+      "type": "Feature",
+      "properties": {},
+      "geometry": {
+        "type": "LineString",
+        "coordinates": [
+          [1, 0],
+          [0, 0]
+        ]
+      }
+    }
+  ]
+}
diff --git a/packages/turf-boolean-parallel/test/true/verticals.geojson b/packages/turf-boolean-parallel/test/true/verticals.geojson
new file mode 100644
index 0000000000..074b854941
--- /dev/null
+++ b/packages/turf-boolean-parallel/test/true/verticals.geojson
@@ -0,0 +1,27 @@
+{
+  "type": "FeatureCollection",
+  "features": [
+    {
+      "type": "Feature",
+      "properties": {},
+      "geometry": {
+        "type": "LineString",
+        "coordinates": [
+          [0, 0],
+          [0, 1]
+        ]
+      }
+    },
+    {
+      "type": "Feature",
+      "properties": {},
+      "geometry": {
+        "type": "LineString",
+        "coordinates": [
+          [1, 0],
+          [1, 1]
+        ]
+      }
+    }
+  ]
+}
diff --git a/packages/turf-boolean-parallel/test/true/verticals3d.geojson b/packages/turf-boolean-parallel/test/true/verticals3d.geojson
new file mode 100644
index 0000000000..a6ab7a2819
--- /dev/null
+++ b/packages/turf-boolean-parallel/test/true/verticals3d.geojson
@@ -0,0 +1,27 @@
+{
+  "type": "FeatureCollection",
+  "features": [
+    {
+      "type": "Feature",
+      "properties": {},
+      "geometry": {
+        "type": "LineString",
+        "coordinates": [
+          [-10, 20, 0],
+          [-10, 10, 0]
+        ]
+      }
+    },
+    {
+      "type": "Feature",
+      "properties": {},
+      "geometry": {
+        "type": "LineString",
+        "coordinates": [
+          [-20, 20, 0],
+          [-20, 10, 0]
+        ]
+      }
+    }
+  ]
+}