Fixed a bug in nearestPointOnLine causing duplicate points to be returned from lineSlice

packages/turf-line-slice/test.ts

@@ -59,3 +59,31 @@ test("turf-nearest-point-on-line -- issue 2023", (t) => {
   );
   t.end();
 });
+
+test("issue 2946 - lineSlice didn't introduce duplicate points", (t) => {
+  // Test case copied from https://github.com/Turfjs/turf/issues/2946
+  // Values rounded to lower precision for realism. Same behaviour as
+  // originally reported though.
+  const startPt = point([2, 0]);
+  const endPt = point([2, 2]);
+  const line = lineString([
+    [2.999848, 0.000152],
+    [2, -1],
+    [2, 2],
+  ]);
+
+  const r1 = lineSlice(startPt, endPt, line);
+  t.equal(
+    r1.geometry.coordinates.length,
+    2,
+    "Two points only in the linestring"
+  );
+
+  // This part of the issue report should have already been fixed by the
+  // recent PR #2940.
+  t.doesNotThrow(() => {
+    const r2 = lineSlice(startPt, endPt, r1);
+  }, "Does not throw when called again on first result");
+
+  t.end();
+});

packages/turf-line-slice/test/out/route2.geojson

@@ -6355,7 +6355,6 @@
           [-112.622281, 45.973317],
           [-112.622078, 45.970234],
           [-112.619831, 45.970225],
-          [-112.614288, 45.970203],
           [-112.614288, 45.970203]
         ]
       }

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

@@ -75,6 +75,7 @@ function nearestPointOnLine<G extends LineString | MultiLineString>(
     lines,
     function (line: any, _featureIndex: number, multiFeatureIndex: number) {
       const coords: any = getCoords(line);
+      const maxSegmentIndex = coords.length - 2;
 
       for (let i = 0; i < coords.length - 1; i++) {
         //start - start of current line section
@@ -117,9 +118,11 @@ function nearestPointOnLine<G extends LineString | MultiLineString>(
             ...intersectPt,
             properties: {
               ...intersectPt.properties,
-              // Legacy behaviour where index progresses to next segment # if we
-              // went with the end point this iteration.
-              index: wasEnd ? i + 1 : i,
+              // Legacy behaviour where index progresses to next segment if we
+              // went with the end point this iteration. Though make sure we
+              // only progress to the beginning of the next segment if one
+              // actually exists.
+              index: wasEnd && i + 1 <= maxSegmentIndex ? i + 1 : i,
             },
           };
         }

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

@@ -48,7 +48,7 @@ test("turf-nearest-point-on-line", (t) => {
 
     if (process.env.REGEN)
       writeJsonFileSync(directories.out + filename, results);
-    t.deepEqual(loadJsonFileSync(directories.out + filename), results, name);
+    t.deepEqual(results, loadJsonFileSync(directories.out + filename), name);
   }
   t.end();
 });
@@ -320,7 +320,7 @@ test("turf-nearest-point-on-line - check dist and index", (t) => {
   const pt = point([-92.110576, 41.040649]);
   const snapped = truncate(nearestPointOnLine(line, pt));
 
-  t.equal(snapped.properties.index, 8, "properties.index");
+  t.equal(snapped.properties.index, 7, "properties.index");
   t.equal(
     Number(snapped.properties.dist.toFixed(6)),
     0.823802,

packages/turf-nearest-point-on-line/test/in/end-point-1.geojson

@@ -0,0 +1,30 @@
+{
+  "type": "FeatureCollection",
+  "features": [
+    {
+      "type": "Feature",
+      "properties": {
+        "description": "Result index should be 2 as there is a third segment and matches to an endpoint bump to the start of the next segment"
+      },
+      "geometry": {
+        "coordinates": [
+          [151.12342, -29.776038],
+          [151.112785, -29.783069],
+          [151.119935, -29.764135],
+          [151.107173, -29.768495]
+        ],
+        "type": "LineString"
+      }
+    },
+    {
+      "type": "Feature",
+      "properties": {
+        "marker-color": "green"
+      },
+      "geometry": {
+        "coordinates": [151.12207, -29.761332],
+        "type": "Point"
+      }
+    }
+  ]
+}

packages/turf-nearest-point-on-line/test/in/end-point-2.geojson

@@ -0,0 +1,29 @@
+{
+  "type": "FeatureCollection",
+  "features": [
+    {
+      "type": "Feature",
+      "properties": {
+        "description": "Result index should be 1 as there is no later segment to bump the index to."
+      },
+      "geometry": {
+        "coordinates": [
+          [151.12342, -29.776038],
+          [151.112785, -29.783069],
+          [151.119935, -29.764135]
+        ],
+        "type": "LineString"
+      }
+    },
+    {
+      "type": "Feature",
+      "properties": {
+        "marker-color": "green"
+      },
+      "geometry": {
+        "coordinates": [151.12207, -29.761332],
+        "type": "Point"
+      }
+    }
+  ]
+}

packages/turf-nearest-point-on-line/test/out/end-point-1.geojson

@@ -0,0 +1,47 @@
+{
+  "type": "FeatureCollection",
+  "features": [
+    {
+      "type": "Feature",
+      "properties": {
+        "description": "Result index should be 2 as there is a third segment and matches to an endpoint bump to the start of the next segment"
+      },
+      "geometry": {
+        "coordinates": [
+          [151.12342, -29.776038],
+          [151.112785, -29.783069],
+          [151.119935, -29.764135],
+          [151.107173, -29.768495]
+        ],
+        "type": "LineString"
+      }
+    },
+    {
+      "type": "Feature",
+      "properties": { "stroke": "#F00", "stroke-width": 6 },
+      "geometry": {
+        "type": "LineString",
+        "coordinates": [
+          [151.119935, -29.764135],
+          [151.12207, -29.761332]
+        ]
+      }
+    },
+    {
+      "type": "Feature",
+      "properties": { "marker-color": "green" },
+      "geometry": { "coordinates": [151.12207, -29.761332], "type": "Point" }
+    },
+    {
+      "type": "Feature",
+      "properties": {
+        "dist": 0.373652,
+        "multiFeatureIndex": 0,
+        "location": 3.505821,
+        "index": 2,
+        "marker-color": "#F0F"
+      },
+      "geometry": { "type": "Point", "coordinates": [151.119935, -29.764135] }
+    }
+  ]
+}

packages/turf-nearest-point-on-line/test/out/end-point-2.geojson

@@ -0,0 +1,46 @@
+{
+  "type": "FeatureCollection",
+  "features": [
+    {
+      "type": "Feature",
+      "properties": {
+        "description": "Result index should be 1 as there is no later segment to bump the index to."
+      },
+      "geometry": {
+        "coordinates": [
+          [151.12342, -29.776038],
+          [151.112785, -29.783069],
+          [151.119935, -29.764135]
+        ],
+        "type": "LineString"
+      }
+    },
+    {
+      "type": "Feature",
+      "properties": { "stroke": "#F00", "stroke-width": 6 },
+      "geometry": {
+        "type": "LineString",
+        "coordinates": [
+          [151.119935, -29.764135],
+          [151.12207, -29.761332]
+        ]
+      }
+    },
+    {
+      "type": "Feature",
+      "properties": { "marker-color": "green" },
+      "geometry": { "coordinates": [151.12207, -29.761332], "type": "Point" }
+    },
+    {
+      "type": "Feature",
+      "properties": {
+        "dist": 0.373652,
+        "multiFeatureIndex": 0,
+        "location": 3.505821,
+        "index": 1,
+        "marker-color": "#F0F"
+      },
+      "geometry": { "type": "Point", "coordinates": [151.119935, -29.764135] }
+    }
+  ]
+}

packages/turf-nearest-point-on-line/test/out/multiLine1.geojson

@@ -68,7 +68,7 @@
       "type": "Feature",
       "properties": {
         "dist": 114.725451,
-        "index": 21,
+        "index": 20,
         "multiFeatureIndex": 1,
         "location": 9479.011715,
         "marker-color": "#F0F"