Fix wall segments for tiny extruded geometry

CHANGES.md

@@ -20,12 +20,12 @@ Change Log
 * Reduces size of approximateTerrainHeights.json by rounding the numbers [#7959](https://github.com/AnalyticalGraphicsInc/cesium/pull/7959)
 * Fixed undefined `quadDetails` error from zooming into the map really close. [#8011](https://github.com/AnalyticalGraphicsInc/cesium/pull/8011)
 * Fixed triangulation bug in polygons using `ArcType.RHUMB`. [#8042](https://github.com/AnalyticalGraphicsInc/cesium/issues/8042)
+* Fixed a bug where extruded polygons would sometimes be missing segments. [#8035](https://github.com/AnalyticalGraphicsInc/cesium/pull/8035)
 * 3D Tiles geometric error now scales with transform. [#8182](https://github.com/AnalyticalGraphicsInc/cesium/pull/8182)
 * Fixed per-feature post processing from sometimes selecting the wrong feature. [#7929](https://github.com/AnalyticalGraphicsInc/cesium/pull/7929)
 * Fixed labels not showing for individual entities in data sources when clustering is enabled. [#6087](https://github.com/AnalyticalGraphicsInc/cesium/issues/6087)
 * Fixed a crash for 3D Tiles that have zero volume. [#7945](https://github.com/AnalyticalGraphicsInc/cesium/pull/7945)
 
-
 ### 1.61 - 2019-09-03
 
 ##### Additions :tada:

Source/Core/PolygonGeometryLibrary.js

@@ -591,7 +591,8 @@ define([
 
             p1 = Cartesian3.fromArray(edgePositions, UL * 3, p1Scratch);
             p2 = Cartesian3.fromArray(edgePositions, UR * 3, p2Scratch);
-            if (Cartesian3.equalsEpsilon(p1, p2, CesiumMath.EPSILON14, CesiumMath.EPSILON6)) {
+            if (Cartesian3.equalsEpsilon(p1, p2, CesiumMath.EPSILON10, CesiumMath.EPSILON10)) {
+                //skip corner
                 continue;
             }
 

Specs/Core/PolygonGeometrySpec.js

@@ -1039,6 +1039,44 @@ describe('Core/PolygonGeometry', function() {
         expect(geometry.attributes.normal).toBeUndefined();
     });
 
+    it('does not include indices for extruded walls that are too small', function() {
+        var positions = Cartesian3.fromDegreesArray([
+            7.757161063097392, 48.568676799636634,
+            7.753968290229146, 48.571796467099077,
+            7.755340073906587, 48.571948854067948,
+            7.756263393414589, 48.571947951609708,
+            7.756894446412183, 48.569396703043992
+        ]);
+
+        var pRhumb = PolygonGeometry.createGeometry(PolygonGeometry.fromPositions({
+            vertexFormat : VertexFormat.POSITION_ONLY,
+            positions : positions,
+            extrudedHeight: 1000,
+            closeTop: false,
+            closeBottom: false,
+            arcType: ArcType.RHUMB
+        }));
+
+        var numVertices = 20;
+        var numTriangles = 10; //5 wall segments, 2 triangles each wall
+        expect(pRhumb.attributes.position.values.length).toEqual(numVertices * 3);
+        expect(pRhumb.indices.length).toEqual(numTriangles * 3);
+
+        var pGeodesic = PolygonGeometry.createGeometry(PolygonGeometry.fromPositions({
+            vertexFormat : VertexFormat.POSITION_ONLY,
+            positions : positions,
+            extrudedHeight: 1000,
+            closeTop: false,
+            closeBottom: false,
+            arcType: ArcType.GEODESIC
+        }));
+
+        numVertices = 20;
+        numTriangles = 10;
+        expect(pGeodesic.attributes.position.values.length).toEqual(numVertices * 3);
+        expect(pGeodesic.indices.length).toEqual(numTriangles * 3);
+    });
+
     it('computing rectangle property', function() {
         var p = new PolygonGeometry({
             vertexFormat : VertexFormat.POSITION_AND_ST,