fix mitering bug with ground polylines over long distances

CHANGES.md

@@ -4,10 +4,11 @@ Change Log
 ### 1.59 - 2019-07-01
 
 ##### Fixes :wrench:
+* Fixed a bug that caused missing segments for ground polylines with coplanar points over large distances and problems with polylines containing duplicate points. [#7885](https:/AnalyticalGraphicsInc/cesium//pull/7885)
 * Fixed a bug where billboards were not pickable when zoomed out completely in 2D View. [#7908](https:/AnalyticalGraphicsInc/cesium/pull/7908)
 
 ### 1.58.1 - 2018-06-03
-_This is an npm-only release to fix a publishing issue__
+_This is an npm-only release to fix a publishing issue_
 
 ### 1.58 - 2019-06-03
 
@@ -22,7 +23,7 @@ _This is an npm-only release to fix a publishing issue__
 ##### Fixes :wrench:
 * Fixed an edge case where Cesium would provide ion access token credentials to non-ion servers if the actual asset entrypoint was being hosted by ion. [#7839](https:/AnalyticalGraphicsInc/cesium/pull/7839)
 * Fixed a bug that caused Cesium to request non-existent tiles for terrain tilesets lacking tile availability, i.e. a `layer.json` file.
-* Fixed memory leak when removing entities that had a `HeightReference` of `CLAMP_TO_GROUND` or `RELATIVE_TO_GROUND`. This includes when removing a `DataSource`. 
+* Fixed memory leak when removing entities that had a `HeightReference` of `CLAMP_TO_GROUND` or `RELATIVE_TO_GROUND`. This includes when removing a `DataSource`.
 * Fixed 3D Tiles credits not being shown in the data attribution box. [#7877](https:/AnalyticalGraphicsInc/cesium/pull/7877)
 
 ### 1.57 - 2019-05-01

Source/Core/GroundPolylineGeometry.js

@@ -353,41 +353,42 @@ define([
  return result;
  }
 
+ function tangentDirection(target, origin, up, result) {
+ result = direction(target, origin, result);
+
+ // orthogonalize
+ result = Cartesian3.cross(result, up, result);
+ result = Cartesian3.normalize(result, result);
+ result = Cartesian3.cross(up, result, result);
+ return result;
+ }
+
  var toPreviousScratch = new Cartesian3();
  var toNextScratch = new Cartesian3();
  var forwardScratch = new Cartesian3();
- var coplanarNormalScratch = new Cartesian3();
- var coplanarPlaneScratch = new Plane(Cartesian3.UNIT_X, 0.0);
  var vertexUpScratch = new Cartesian3();
  var cosine90 = 0.0;
+ var cosine180 = -1.0;
  function computeVertexMiterNormal(previousBottom, vertexBottom, vertexTop, nextBottom, result) {
  var up = direction(vertexTop, vertexBottom, vertexUpScratch);
- var toPrevious = direction(previousBottom, vertexBottom, toPreviousScratch);
- var toNext = direction(nextBottom, vertexBottom, toNextScratch);
-
- // Check if points are coplanar in a right-side-pointing plane that contains "up."
- // This is roughly equivalent to the points being colinear in cartographic space.
- var coplanarNormal = Cartesian3.cross(up, toPrevious, coplanarNormalScratch);
- coplanarNormal = Cartesian3.normalize(coplanarNormal, coplanarNormal);
- var coplanarPlane = Plane.fromPointNormal(vertexBottom, coplanarNormal, coplanarPlaneScratch);
- var nextBottomDistance = Plane.getPointDistance(coplanarPlane, nextBottom);
- if (CesiumMath.equalsEpsilon(nextBottomDistance, 0.0, CesiumMath.EPSILON7)) {
- // If the points are coplanar, point the normal in the direction of the plane
- Cartesian3.clone(coplanarNormal, result);
- return result;
+
+ // Compute vectors pointing towards neighboring points but tangent to this point on the ellipsoid
+ var toPrevious = tangentDirection(previousBottom, vertexBottom, up, toPreviousScratch);
+ var toNext = tangentDirection(nextBottom, vertexBottom, up, toNextScratch);
+
+ // Check if tangents are almost opposite - if so, no need to miter.
+ if (CesiumMath.equalsEpsilon(Cartesian3.dot(toPrevious, toNext), cosine180, CesiumMath.EPSILON5)) {
+ result = Cartesian3.cross(up, toPrevious, result);
+ result = Cartesian3.normalize(result, result);
+ return result;
  }
 
- // Average directions to previous and to next
+ // Average directions to previous and to next in the plane of Up
  result = Cartesian3.add(toNext, toPrevious, result);
  result = Cartesian3.normalize(result, result);
 
- // Rotate this direction to be orthogonal to up
- var forward = Cartesian3.cross(up, result, forwardScratch);
- Cartesian3.normalize(forward, forward);
- Cartesian3.cross(forward, up, result);
- Cartesian3.normalize(result, result);
-
  // Flip the normal if it isn't pointing roughly bound right (aka if forward is pointing more "backwards")
+ var forward = Cartesian3.cross(up, result, forwardScratch);
  if (Cartesian3.dot(toNext, forward) < cosine90) {
  result = Cartesian3.negate(result, result);
  }

Specs/Core/GroundPolylineGeometrySpec.js

@@ -287,7 +287,7 @@ defineSuite([
  positions : Cartesian3.fromDegreesArray([
  0.01, 0.0,
  0.02, 0.0,
- 0.01, 0.0
+ 0.01, CesiumMath.EPSILON7
  ]),
  granularity : 0.0
  });
@@ -299,11 +299,10 @@ defineSuite([
 
  var miteredStartNormal = Cartesian3.unpack(startNormalAndForwardOffsetZvalues, 32);
  var miteredEndNormal = Cartesian3.unpack(endNormalAndTextureCoordinateNormalizationXvalues, 0);
- var reverseMiteredEndNormal = Cartesian3.multiplyByScalar(miteredEndNormal, -1.0, new Cartesian3());
 
- expect(Cartesian3.equalsEpsilon(miteredStartNormal, reverseMiteredEndNormal, CesiumMath.EPSILON7)).toBe(true);
+ expect(Cartesian3.equalsEpsilon(miteredStartNormal, miteredEndNormal, CesiumMath.EPSILON7)).toBe(true);
 
- var approximateExpectedMiterNormal = new Cartesian3(0.0, 1.0, 0.0);
+ var approximateExpectedMiterNormal = new Cartesian3(0.0, -1.0, 0.0);
 
  Cartesian3.normalize(approximateExpectedMiterNormal, approximateExpectedMiterNormal);
  expect(Cartesian3.equalsEpsilon(approximateExpectedMiterNormal, miteredStartNormal, CesiumMath.EPSILON2)).toBe(true);