Fix geojson EllipsoidRhumbLine error for duplicated points

CHANGES.md

@@ -1,5 +1,13 @@
 # Change Log
 
+## 1.127 - 2025-03-03
+
+### @cesium/engine
+
+#### Fixes :wrench:
+
+- Fixed error when there are duplicated points in polygon/polyline geometries with `ArcType.RHUMB` [#12460](https://github.com/CesiumGS/cesium/pull/12460)
+
 ## 1.126 - 2025-02-03
 
 ### @cesium/engine

packages/engine/Source/Core/EllipsoidRhumbLine.js

@@ -562,7 +562,7 @@ EllipsoidRhumbLine.prototype.interpolateUsingFraction = function (
 /**
  * Provides the location of a point at the indicated distance along the rhumb line.
  *
- * @param {number} distance The distance from the inital point to the point of interest along the rhumbLine.
+ * @param {number} distance The distance from the initial point to the point of interest along the rhumbLine.
  * @param {Cartographic} [result] The object in which to store the result.
  * @returns {Cartographic} The location of the point along the rhumb line.
  *

packages/engine/Source/Core/PolygonGeometryLibrary.js

@@ -312,6 +312,18 @@ PolygonGeometryLibrary.subdivideTexcoordRhumbLine = function (
   return texcoords;
 };
 
+/**
+ * Subdivide the line between 2 points every minDistance length
+ * If the points are already closer than minDistance the first will be returned
+ *
+ * @private
+ * @param {Ellipsoid} ellipsoid
+ * @param {Cartesian3} p0 start point
+ * @param {Cartesian3} p1 end point
+ * @param {number} minDistance minimum distance between points in radians
+ * @param {number[]} [result] if provided positions will be packed into this array starting at index 0
+ * @returns {number[]} Cartesian3 positions packed into an array
+ */
 PolygonGeometryLibrary.subdivideRhumbLine = function (
   ellipsoid,
   p0,
@@ -323,15 +335,25 @@ PolygonGeometryLibrary.subdivideRhumbLine = function (
   const c1 = ellipsoid.cartesianToCartographic(p1, scratchCartographic1);
   const rhumb = new EllipsoidRhumbLine(c0, c1, ellipsoid);
 
+  if (!defined(result)) {
+    result = [];
+  }
+
+  if (rhumb.surfaceDistance <= minDistance) {
+    // no need to try and subdivide a line that's already shorter than the min distance
+    // this also inherently handles duplicated points which would have 0 distance
+    result.length = 3;
+    result[0] = p0.x;
+    result[1] = p0.y;
+    result[2] = p0.z;
+    return result;
+  }
+
   const n = rhumb.surfaceDistance / minDistance;
   const countDivide = Math.max(0, Math.ceil(CesiumMath.log2(n)));
   const numVertices = Math.pow(2, countDivide);
   const distanceBetweenVertices = rhumb.surfaceDistance / numVertices;
 
-  if (!defined(result)) {
-    result = [];
-  }
-
   const positions = result;
   positions.length = numVertices * 3;
 

packages/engine/Specs/Core/PolygonGeometryLibrarySpec.js

@@ -7,7 +7,58 @@ import {
 } from "../../index.js";
 
 describe("Core/PolygonGeometryLibrary", function () {
-  describe("splitPolygonByPlane", function () {
+  describe("subdivideRhumbLine", () => {
+    it("returns first point if both points are the same", function () {
+      const p0 = new Cartesian3(3813220.0, -5085291.0, 527179.0);
+      const p1 = new Cartesian3(3813220.0, -5085291.0, 527179.0);
+      const positions = PolygonGeometryLibrary.subdivideRhumbLine(
+        Ellipsoid.WGS84,
+        p0,
+        p1,
+        2,
+      );
+      expect(positions.length).toEqual(3);
+      expect(positions).toEqual([3813220.0, -5085291.0, 527179.0]);
+    });
+
+    it("returns first point if the points are closer than minDistance", function () {
+      const p0 = new Cartesian3(3813220.0, -5085291.0, 527179.0);
+      const p1 = new Cartesian3(3813220.0, -5085291.0, 527179.0 + 1);
+      // actual surface distance is ~0.997
+      const positions = PolygonGeometryLibrary.subdivideRhumbLine(
+        Ellipsoid.WGS84,
+        p0,
+        p1,
+        2,
+      );
+      expect(positions.length).toEqual(3);
+      expect(positions).toEqual([3813220.0, -5085291.0, 527179.0]);
+    });
+
+    it("subdivides the line between 2 points", function () {
+      const p0 = new Cartesian3(3813220.0, -5085291.0, 527179.0);
+      const p1 = new Cartesian3(3813220.0, -5085291.0, 527179.0 + 5);
+      // actual surface distance is ~4.983
+      const positions = PolygonGeometryLibrary.subdivideRhumbLine(
+        Ellipsoid.WGS84,
+        p0,
+        p1,
+        2,
+      );
+      expect(positions.length).toEqual(12);
+      expect(positions).toEqualEpsilon(
+        [
+          3813220.447295841, -5085291.596511482, 527179.0622555692,
+          3813220.3851130935, -5085291.513584885, 527180.3036009098,
+          3813220.3229302, -5085291.430658091, 527181.5449462304,
+          3813220.2607471617, -5085291.347731101, 527182.7862915307,
+        ],
+        CesiumMath.EPSILON7,
+      );
+    });
+  });
+
+  describe("splitPolygonsOnEquator", function () {
     it("splits a simple polygon at the equator", function () {
       const positions = Cartesian3.unpackArray([
         3813220.0, -5085291.0, 527179.0, 3701301.0, -5097773.0, -993503.0,