Fix vertical rhumb line when using PolylineGeometry

CHANGES.md

@@ -6,6 +6,7 @@
 
 - Fixed 3D Tileset replacement refinement when leaf is empty. [#8996](https://github.com/CesiumGS/cesium/pull/8996)
 - Fixed a bug in the assessment of terrain tile visibility [#9033](https://github.com/CesiumGS/cesium/issues/9033)
+- Fixed vertical polylines with `arcType: ArcType.RHUMB`, including lines drawn via GeoJSON. [#9028](https://github.com/CesiumGS/cesium/pull/9028)
 
 ### 1.71 - 2020-07-01
 

Source/Core/PolylinePipeline.js

@@ -25,8 +25,10 @@ PolylinePipeline.numberOfPointsRhumbLine = function (p0, p1, granularity) {
   var radiansDistanceSquared =
     Math.pow(p0.longitude - p1.longitude, 2) +
     Math.pow(p0.latitude - p1.latitude, 2);
-  return Math.ceil(
-    Math.sqrt(radiansDistanceSquared / (granularity * granularity))
+
+  return Math.max(
+    1,
+    Math.ceil(Math.sqrt(radiansDistanceSquared / (granularity * granularity)))
   );
 };
 

Specs/Core/PolylineGeometrySpec.js

@@ -5,6 +5,7 @@ import { Ellipsoid } from "../../Source/Cesium.js";
 import { PolylineGeometry } from "../../Source/Cesium.js";
 import { VertexFormat } from "../../Source/Cesium.js";
 import createPackableSpecs from "../createPackableSpecs.js";
+import CesiumMath from "../../Source/Core/Math.js";
 
 describe("Core/PolylineGeometry", function () {
   it("constructor throws with no positions", function () {
@@ -184,6 +185,64 @@ describe("Core/PolylineGeometry", function () {
     expect(geometry).not.toBeDefined();
   });
 
+  it("createGeometry returns positions if their endpoints'longtitude and latitude are the same for rhumb line", function () {
+    var positions = Cartesian3.fromDegreesArrayHeights([
+      30.0,
+      30.0,
+      10.0,
+      30.0,
+      30.0,
+      5.0,
+    ]);
+    var geometry = PolylineGeometry.createGeometry(
+      new PolylineGeometry({
+        positions: positions,
+        width: 10.0,
+        vertexFormat: VertexFormat.POSITION_ONLY,
+        arcType: ArcType.RHUMB,
+      })
+    );
+
+    var attributePositions = geometry.attributes.position.values;
+    var geometryPosition = new Cartesian3();
+
+    Cartesian3.fromArray(attributePositions, 0, geometryPosition);
+    expect(
+      Cartesian3.equalsEpsilon(
+        geometryPosition,
+        positions[0],
+        CesiumMath.EPSILON7
+      )
+    ).toBe(true);
+
+    Cartesian3.fromArray(attributePositions, 3, geometryPosition);
+    expect(
+      Cartesian3.equalsEpsilon(
+        geometryPosition,
+        positions[0],
+        CesiumMath.EPSILON7
+      )
+    ).toBe(true);
+
+    Cartesian3.fromArray(attributePositions, 6, geometryPosition);
+    expect(
+      Cartesian3.equalsEpsilon(
+        geometryPosition,
+        positions[1],
+        CesiumMath.EPSILON7
+      )
+    ).toBe(true);
+
+    Cartesian3.fromArray(attributePositions, 9, geometryPosition);
+    expect(
+      Cartesian3.equalsEpsilon(
+        geometryPosition,
+        positions[1],
+        CesiumMath.EPSILON7
+      )
+    ).toBe(true);
+  });
+
   var positions = [
     new Cartesian3(1, 2, 3),
     new Cartesian3(4, 5, 6),