fix: randomLineString does not take max_rotation option into account (#2893)

packages/turf-random/index.ts

@@ -15,6 +15,7 @@ import {
   polygon,
   validateBBox,
 } from "@turf/helpers";
+import destination from "@turf/destination";
 
 /**
  * Returns a random position within a {@link BBox|bounding box}.
@@ -233,20 +234,18 @@ function randomLineString(
   for (let i = 0; i < count; i++) {
     const startingPoint = randomPositionUnchecked(bbox);
     const vertices = [startingPoint];
-    for (let j = 0; j < num_vertices - 1; j++) {
-      const priorAngle =
-        j === 0
-          ? Math.random() * 2 * Math.PI
-          : Math.tan(
-              (vertices[j][1] - vertices[j - 1][1]) /
-                (vertices[j][0] - vertices[j - 1][0])
-            );
-      const angle = priorAngle + (Math.random() - 0.5) * max_rotation * 2;
-      const distance = Math.random() * max_length;
-      vertices.push([
-        vertices[j][0] + distance * Math.cos(angle),
-        vertices[j][1] + distance * Math.sin(angle),
-      ]);
+    var priorBearing = Math.random() * 360;
+    for (var j = 0; j < num_vertices - 1; j++) {
+      var newBearing =
+        priorBearing +
+        ((Math.random() - 0.5) * max_rotation * 2 * 180) / Math.PI;
+      if (newBearing > 180) newBearing -= 360;
+      var distance = Math.random() * max_length;
+      const vertex = destination(vertices[j], distance, newBearing, {
+        units: "degrees",
+      });
+      priorBearing = newBearing;
+      vertices.push(vertex.geometry.coordinates);
     }
     features.push(lineString(vertices));
   }

packages/turf-random/package.json

@@ -49,6 +49,8 @@
     "test:tape": "tsx test.ts"
   },
   "devDependencies": {
+    "@turf/bearing": "workspace:*",
+    "@turf/distance": "workspace:*",
     "@types/benchmark": "^2.1.5",
     "@types/tape": "^5.8.1",
     "benchmark": "^2.1.4",
@@ -60,6 +62,7 @@
     "typescript": "^5.8.3"
   },
   "dependencies": {
+    "@turf/destination": "workspace:*",
     "@turf/helpers": "workspace:*",
     "@types/geojson": "^7946.0.10",
     "tslib": "^2.8.1"

packages/turf-random/test.ts

@@ -1,4 +1,6 @@
 import test from "tape";
+import distance from "@turf/distance";
+import bearing from "@turf/bearing";
 import {
   randomPoint,
   randomPolygon,
@@ -30,7 +32,7 @@ test("random(polygons, 10)", (t) => {
   t.end();
 });
 
-test("random(polygons, 1, {num_vertices})", (t) => {
+test("random(polygons, 10, {num_vertices})", (t) => {
   var points = randomPolygon(10, { num_vertices: 23 });
   t.equal(points.type, "FeatureCollection", "is a featurecollection");
   t.equal(points.features.length, 10, "right number of features");
@@ -77,3 +79,106 @@ test("bbox input gets validated", (t) => {
   }, "randomPosition checks bbox validity");
   t.end();
 });
+
+test("random(lines)", (t) => {
+  var lines = randomLineString();
+  t.equal(lines.type, "FeatureCollection", "is a featurecollection");
+  t.equal(lines.features.length, 1, "right number of features");
+  t.equal(
+    lines.features[0].geometry.type,
+    "LineString",
+    "feature type correct"
+  );
+  t.end();
+});
+
+test("random(lines, 10)", (t) => {
+  var lines = randomLineString(10);
+  t.equal(lines.type, "FeatureCollection", "is a featurecollection");
+  t.equal(lines.features.length, 10, "right number of features");
+  t.equal(
+    lines.features[0].geometry.type,
+    "LineString",
+    "feature type correct"
+  );
+  t.end();
+});
+
+test("random(lines, 10, {num_vertices})", (t) => {
+  var lines = randomLineString(10, { num_vertices: 10 });
+  t.equal(lines.type, "FeatureCollection", "is a featurecollection");
+  t.equal(lines.features.length, 10, "right number of features");
+  t.equal(lines.features[0].geometry.coordinates.length, 10, "num vertices");
+  t.end();
+});
+
+test("random(lines, 10, {bbox})", (t) => {
+  var lines = randomLineString(10, { bbox: [0, 0, 0, 0] });
+  t.equal(lines.type, "FeatureCollection", "is a featurecollection");
+  t.equal(lines.features.length, 10, "right number of features");
+  t.equal(
+    lines.features[0].geometry.type,
+    "LineString",
+    "feature type correct"
+  );
+  t.deepEqual(
+    lines.features[0].geometry.coordinates[0],
+    [0, 0],
+    "feature type correct"
+  );
+  t.end();
+});
+
+test("random(lines, 10, {max_length})", (t) => {
+  var lines = randomLineString(10, { max_length: 0.1 });
+  t.equal(lines.type, "FeatureCollection", "is a featurecollection");
+  t.equal(lines.features.length, 10, "right number of features");
+  t.equal(
+    lines.features[0].geometry.type,
+    "LineString",
+    "feature type correct"
+  );
+  let ok = true;
+  for (let i = 1; i < lines.features[0].geometry.coordinates.length; i++) {
+    const length = distance(
+      lines.features[0].geometry.coordinates[i - 1],
+      lines.features[0].geometry.coordinates[i],
+      { units: "degrees" }
+    );
+    if (length > 0.1) ok = false;
+  }
+  t.ok(ok, "randomLineString ensures max_length");
+  t.end();
+});
+
+test("random(lines, 10, {max_rotation})", (t) => {
+  var lines = randomLineString(10, { max_rotation: Math.PI / 10 });
+  t.equal(lines.type, "FeatureCollection", "is a featurecollection");
+  t.equal(lines.features.length, 10, "right number of features");
+  t.equal(
+    lines.features[0].geometry.type,
+    "LineString",
+    "feature type correct"
+  );
+  let ok = true;
+  for (let i = 2; i < lines.features[0].geometry.coordinates.length; i++) {
+    // Compute the differential angle with the previous segment
+    let bearing1 = bearing(
+      lines.features[0].geometry.coordinates[i - 2],
+      lines.features[0].geometry.coordinates[i - 1]
+    );
+    //if (bearing1 < 0) bearing1 += 360;
+    let bearing2 = bearing(
+      lines.features[0].geometry.coordinates[i - 1],
+      lines.features[0].geometry.coordinates[i]
+    );
+    //if (bearing2 < 0) bearing2 += 360;
+    const difference =
+      bearing1 * bearing2 < 0
+        ? bearing2 + bearing1
+        : Math.abs(bearing2 - bearing1);
+    if (difference > 18) ok = false;
+  }
+  t.ok(ok, "randomLineString ensures max_rotation");
+  t.end();
+});