Fixes to multiple modules that were performing scalar (2D) calculations when they should have been doing spherical (3D). Most changes were to nearestPointOnLine. pointToLineDistance now uses nearestPointOnLine for spherical calculations. Flow on corrections impacted lineSlice and nearestPointToLine as well.

Tidied up some tests - fixed module name in test definitions, added a benchmark overall time in a few places for easier comparisons.

Author: smallsaucepan

packages/turf-line-slice/test.ts

@@ -5,7 +5,7 @@ import { fileURLToPath } from "url";
 import { loadJsonFileSync } from "load-json-file";
 import { writeJsonFileSync } from "write-json-file";
 import { truncate } from "@turf/truncate";
-import { featureCollection } from "@turf/helpers";
+import { featureCollection, point, lineString } from "@turf/helpers";
 import { lineSlice } from "./index.js";
 
 const __dirname = path.dirname(fileURLToPath(import.meta.url));
@@ -38,3 +38,24 @@ test("turf-line-slice", (t) => {
   }
   t.end();
 });
+
+test("turf-nearest-point-on-line -- issue 2023", (t) => {
+  const ptStart = point([3.69140625, 51.72702815704774]);
+  const ptEnd = point([0.31936718356317106, 47.93913163509963]);
+  const line = lineString([
+    [3.69140625, 51.72702815704774],
+    [-5.3173828125, 41.60722821271717],
+  ]);
+
+  const slice = lineSlice(ptStart, ptEnd, line);
+
+  t.deepEqual(
+    truncate(slice, { precision: 8 }).geometry.coordinates,
+    [
+      [3.69140625, 51.72702816],
+      [-0.03079923, 48.08596086],
+    ],
+    "slice should be [[3.69140625, 51.72702816], [-0.03079923, 48.08596086]]"
+  );
+  t.end();
+});

packages/turf-line-slice/test/out/line1.geojson

@@ -38,9 +38,9 @@
       "geometry": {
         "type": "LineString",
         "coordinates": [
-          [-97.835729, 22.247393],
+          [-97.835747, 22.247595],
           [-97.820892, 22.17596],
-          [-97.738467, 22.051207]
+          [-97.738477, 22.051413]
         ]
       }
     }

packages/turf-line-slice/test/out/line2.geojson

@@ -37,8 +37,8 @@
       "geometry": {
         "type": "LineString",
         "coordinates": [
-          [0.049987, 0.049987],
-          [0.849858, 0.849858]
+          [0.05, 0.050008],
+          [0.849981, 0.850017]
         ]
       }
     }

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

@@ -3796,7 +3796,7 @@
       "geometry": {
         "type": "LineString",
         "coordinates": [
-          [-111.895792, 48.877416],
+          [-111.895843, 48.877468],
           [-111.878176, 48.860393],
           [-111.867242, 48.849753],
           [-111.866486, 48.849013],

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

@@ -2,7 +2,7 @@ import fs from "fs";
 import path from "path";
 import { fileURLToPath } from "url";
 import { loadJsonFileSync } from "load-json-file";
-import Benchmark from "benchmark";
+import Benchmark, { Event } from "benchmark";
 import { nearestPointOnLine } from "./index.js";
 
 const __dirname = path.dirname(fileURLToPath(import.meta.url));
@@ -29,10 +29,19 @@ const fixtures = fs.readdirSync(directory).map((filename) => {
  * route1 x 195 ops/sec ±2.23% (80 runs sampled)
  * route2 x 218 ops/sec ±2.42% (78 runs sampled)
  */
+let totalTime = 0.0;
 const suite = new Benchmark.Suite("turf-nearest-point-on-line");
 for (const { name, geojson } of fixtures) {
   const [line, point] = geojson.features;
-  suite.add(name, () => nearestPointOnLine(line, point));
+  suite.add(name, () => nearestPointOnLine(line, point), {
+    onComplete: (e: Event) =>
+      (totalTime = totalTime += e.target.times?.elapsed),
+  });
 }
 
-suite.on("cycle", (e) => console.log(String(e.target))).run();
+suite
+  .on("cycle", (e: Event) => console.log(String(e.target)))
+  .on("complete", () =>
+    console.log(`completed in ${totalTime.toFixed(2)} seconds`)
+  )
+  .run();

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

@@ -1,11 +1,8 @@
-import { Feature, Point, LineString, MultiLineString } from "geojson";
-import { bearing } from "@turf/bearing";
+import { Feature, Point, Position, LineString, MultiLineString } from "geojson";
 import { distance } from "@turf/distance";
-import { destination } from "@turf/destination";
-import { lineIntersect as lineIntersects } from "@turf/line-intersect";
 import { flattenEach } from "@turf/meta";
-import { point, lineString, Coord, Units } from "@turf/helpers";
-import { getCoords } from "@turf/invariant";
+import { point, Coord, Units } from "@turf/helpers";
+import { getCoord, getCoords } from "@turf/invariant";
 
 /**
  * Takes a {@link Point} and a {@link LineString} and calculates the closest Point on the (Multi)LineString.
@@ -51,6 +48,8 @@ function nearestPointOnLine<G extends LineString | MultiLineString>(
     throw new Error("lines and pt are required arguments");
   }
 
+  const ptPos = getCoord(pt);
+
   let closestPt: Feature<
     Point,
     { dist: number; index: number; multiFeatureIndex: number; location: number }
@@ -68,80 +67,48 @@ function nearestPointOnLine<G extends LineString | MultiLineString>(
       const coords: any = getCoords(line);
 
       for (let i = 0; i < coords.length - 1; i++) {
-        //start
+        //start - start of current line section
         const start: Feature<Point, { dist: number }> = point(coords[i]);
         start.properties.dist = distance(pt, start, options);
-        //stop
+        const startPos = getCoord(start);
+
+        //stop - end of current line section
         const stop: Feature<Point, { dist: number }> = point(coords[i + 1]);
         stop.properties.dist = distance(pt, stop, options);
+        const stopPos = getCoord(stop);
+
         // sectionLength
         const sectionLength = distance(start, stop, options);
-        //perpendicular
-        const heightDistance = Math.max(
-          start.properties.dist,
-          stop.properties.dist
-        );
-        const direction = bearing(start, stop);
-        const perpendicularPt1 = destination(
-          pt,
-          heightDistance,
-          direction + 90,
-          options
-        );
-        const perpendicularPt2 = destination(
-          pt,
-          heightDistance,
-          direction - 90,
-          options
-        );
-        const intersect = lineIntersects(
-          lineString([
-            perpendicularPt1.geometry.coordinates,
-            perpendicularPt2.geometry.coordinates,
-          ]),
-          lineString([start.geometry.coordinates, stop.geometry.coordinates])
-        );
+        let intersectPos: Position;
+        let wasEnd: boolean;
+
+        // Short circuit if snap point is start or end position of the line
+        // segment.
+        if (startPos[0] === ptPos[0] && startPos[1] === ptPos[1]) {
+          [intersectPos, , wasEnd] = [startPos, undefined, false];
+        } else if (stopPos[0] === ptPos[0] && stopPos[1] === ptPos[1]) {
+          [intersectPos, , wasEnd] = [stopPos, undefined, true];
+        } else {
+          // Otherwise, find the nearest point the hard way.
+          [intersectPos, , wasEnd] = nearestPointOnSegment(
+            start.geometry.coordinates,
+            stop.geometry.coordinates,
+            getCoord(pt)
+          );
+        }
         let intersectPt:
           | Feature<
               Point,
               { dist: number; multiFeatureIndex: number; location: number }
             >
           | undefined;
 
-        if (intersect.features.length > 0 && intersect.features[0]) {
-          intersectPt = {
-            ...intersect.features[0],
-            properties: {
-              dist: distance(pt, intersect.features[0], options),
-              multiFeatureIndex: multiFeatureIndex,
-              location:
-                length + distance(start, intersect.features[0], options),
-            },
-          };
-        }
-
-        if (start.properties.dist < closestPt.properties.dist) {
-          closestPt = {
-            ...start,
-            properties: {
-              ...start.properties,
-              index: i,
-              multiFeatureIndex: multiFeatureIndex,
-              location: length,
-            },
-          };
-        }
-
-        if (stop.properties.dist < closestPt.properties.dist) {
-          closestPt = {
-            ...stop,
-            properties: {
-              ...stop.properties,
-              index: i + 1,
-              multiFeatureIndex: multiFeatureIndex,
-              location: length + sectionLength,
-            },
-          };
+        if (intersectPos) {
+          intersectPt = point(intersectPos, {
+            dist: distance(pt, intersectPos, options),
+            multiFeatureIndex: multiFeatureIndex,
+            location: length + distance(start, intersectPos, options),
+          });
         }
 
         if (
@@ -150,9 +117,15 @@ function nearestPointOnLine<G extends LineString | MultiLineString>(
         ) {
           closestPt = {
             ...intersectPt,
-            properties: { ...intersectPt.properties, index: i },
+            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,
+            },
           };
         }
+
         // update length
         length += sectionLength;
       }
@@ -162,5 +135,126 @@ function nearestPointOnLine<G extends LineString | MultiLineString>(
   return closestPt;
 }
 
+type Vector = [number, number, number];
+
+function dot(v1: Vector, v2: Vector): number {
+  const [v1x, v1y, v1z] = v1;
+  const [v2x, v2y, v2z] = v2;
+  return v1x * v2x + v1y * v2y + v1z * v2z;
+}
+
+// https://en.wikipedia.org/wiki/Cross_product
+function cross(v1: Vector, v2: Vector): Vector {
+  const [v1x, v1y, v1z] = v1;
+  const [v2x, v2y, v2z] = v2;
+  return [v1y * v2z - v1z * v2y, v1z * v2x - v1x * v2z, v1x * v2y - v1y * v2x];
+}
+
+function magnitude(v: Vector) {
+  return Math.sqrt(Math.pow(v[0], 2) + Math.pow(v[1], 2) + Math.pow(v[2], 2));
+}
+
+function angle(v1: Vector, v2: Vector): number {
+  const theta = dot(v1, v2) / (magnitude(v1) * magnitude(v2));
+  return Math.acos(Math.min(Math.max(theta, -1), 1));
+}
+
+function toRadians(degrees: number) {
+  return degrees * (Math.PI / 180);
+}
+
+function toDegrees(radians: number) {
+  return radians * (180 / Math.PI);
+}
+
+function lngLatToVector(a: Position): Vector {
+  const lat = toRadians(a[1]);
+  const lng = toRadians(a[0]);
+  return [
+    Math.cos(lat) * Math.cos(lng),
+    Math.cos(lat) * Math.sin(lng),
+    Math.sin(lat),
+  ];
+}
+
+function vectorToLngLat(v: Vector): Position {
+  const [x, y, z] = v;
+  const lat = toDegrees(Math.asin(z));
+  const lng = toDegrees(Math.atan2(y, x));
+
+  return [lng, lat];
+}
+
+function nearestPointOnSegment(
+  posA: Position,
+  posB: Position,
+  posC: Position
+): [Position, boolean, boolean] {
+  // Based heavily on this article on finding cross track distance to an arc:
+  // https://gis.stackexchange.com/questions/209540/projecting-cross-track-distance-on-great-circle
+
+  // Convert lng/lat to spherical coords
+  const A = lngLatToVector(posA); // the vector from 0,0,0 to posA
+  const B = lngLatToVector(posB);
+  const C = lngLatToVector(posC);
+
+  // Components of target point.
+  const [Cx, Cy, Cz] = C;
+
+  // Calculate coefficients.
+  const [D, E, F] = cross(A, B);
+  const a = E * Cz - F * Cy;
+  const b = F * Cx - D * Cz;
+  const c = D * Cy - E * Cx;
+
+  const f = c * E - b * F;
+  const g = a * F - c * D;
+  const h = b * D - a * E;
+
+  const t = 1 / Math.sqrt(Math.pow(f, 2) + Math.pow(g, 2) + Math.pow(h, 2));
+
+  // Vectors to the two points these great circles intersect.
+  const I1: Vector = [f * t, g * t, h * t];
+  const I2: Vector = [-1 * f * t, -1 * g * t, -1 * h * t];
+
+  // Figure out which is the closest intersection to this segment of the great
+  // circle.
+  const angleAB = angle(A, B);
+  const angleAI1 = angle(A, I1);
+  const angleBI1 = angle(B, I1);
+  const angleAI2 = angle(A, I2);
+  const angleBI2 = angle(B, I2);
+
+  let I: Vector;
+
+  if (
+    (angleAI1 < angleAI2 && angleAI1 < angleBI2) ||
+    (angleBI1 < angleAI2 && angleBI1 < angleBI2)
+  ) {
+    I = I1;
+  } else {
+    I = I2;
+  }
+
+  // I is the closest intersection to the segment, though might not actually be
+  // ON the segment.
+
+  // If angle AI or BI is greater than angleAB, I lies on the circle *beyond* A
+  // and B so use the closest of A or B as the intersection
+  if (angle(A, I) > angleAB || angle(B, I) > angleAB) {
+    if (
+      distance(vectorToLngLat(I), vectorToLngLat(A)) <=
+      distance(vectorToLngLat(I), vectorToLngLat(B))
+    ) {
+      return [vectorToLngLat(A), true, false];
+    } else {
+      return [vectorToLngLat(B), false, true];
+    }
+  }
+
+  // As angleAI nor angleBI don't exceed angleAB, I is on the segment
+  return [vectorToLngLat(I), false, false];
+}
+
 export { nearestPointOnLine };
 export default nearestPointOnLine;

packages/turf-nearest-point-on-line/package.json

@@ -61,12 +61,9 @@
     "write-json-file": "^5.0.0"
   },
   "dependencies": {
-    "@turf/bearing": "workspace:^",
-    "@turf/destination": "workspace:^",
     "@turf/distance": "workspace:^",
     "@turf/helpers": "workspace:^",
     "@turf/invariant": "workspace:^",
-    "@turf/line-intersect": "workspace:^",
     "@turf/meta": "workspace:^",
     "@types/geojson": "^7946.0.10",
     "tslib": "^2.6.2"