Added special cases to booleanPointOnLine for zero length lines

booleanPointOnLine was returning false positives for points on the same longitude as zero length lines.

Author: smallsaucepan

packages/turf-boolean-point-on-line/index.ts

@@ -97,6 +97,25 @@ function isPointOnLineSegment(
   } else if (cross !== 0) {
     return false;
   }
+
+  // Special cases for zero length lines
+  // https://github.com/Turfjs/turf/issues/2750
+  if (Math.abs(dxl) === Math.abs(dyl) && Math.abs(dxl) === 0) {
+    // Zero length line.
+    if (excludeBoundary) {
+      // To be on a zero length line pt has to be on the start (and end), BUT we
+      // are excluding start and end from possible matches.
+      return false;
+    }
+    if (pt[0] === lineSegmentStart[0] && pt[1] === lineSegmentStart[1]) {
+      // If point is same as start (and end) it's on the line segment
+      return true;
+    } else {
+      // Otherwise point is somewhere else
+      return false;
+    }
+  }
+
   if (!excludeBoundary) {
     if (Math.abs(dxl) >= Math.abs(dyl)) {
       return dxl > 0 ? x1 <= x && x <= x2 : x2 <= x && x <= x1;

packages/turf-boolean-point-on-line/test.ts

@@ -3,7 +3,10 @@ import path from "path";
 import { fileURLToPath } from "url";
 import test from "tape";
 import { loadJsonFileSync } from "load-json-file";
-import { booleanPointOnLine as pointOnLine } from "./index.js";
+import { point, lineString } from "@turf/helpers";
+import booleanPointOnLine, {
+  booleanPointOnLine as pointOnLine,
+} from "./index.js";
 
 const __dirname = path.dirname(fileURLToPath(import.meta.url));
 
@@ -36,3 +39,33 @@ test("turf-boolean-point-on-line", (t) => {
     });
   t.end();
 });
+
+test("turf-boolean-point-on-line - issue 2750", (t) => {
+  // Issue 2750 was that in the first test below where point is on a different
+  // longitude to a zero length line booleanPointOnLine gave the correct result,
+  // while the second test where a point on the SAME longitude, but nowhere
+  // near, that zero length line incorrectly returned true.
+  t.false(
+    booleanPointOnLine(
+      point([2, 13]),
+      lineString([
+        [1, 1],
+        [1, 1],
+      ])
+    ),
+    "#2750 different longitude point not on zero length line"
+  );
+
+  t.false(
+    booleanPointOnLine(
+      point([1, 13]),
+      lineString([
+        [1, 1],
+        [1, 1],
+      ])
+    ),
+    "#2750 same longitude point not on zero length line"
+  );
+
+  t.end();
+});