GeoJSON with vertical line crashes

[silke-boehler]

When loading the folling Sandcastle example, it will crash with following error:

An error occurred while rendering. Rendering has stopped.
undefined
DeveloperError: Expected right to be typeof object, actual typeof was undefined
Error
at DeveloperError (https://sandcastle.cesium.com/CesiumUnminified/Workers/Check-c4f3a3fc.js:62:17)
at Check.typeOf.object (https://sandcastle.cesium.com/CesiumUnminified/Workers/Check-c4f3a3fc.js:238:17)
at Cartesian3.subtract (https://sandcastle.cesium.com/CesiumUnminified/Workers/Cartesian2-a4e73c05.js:530:13)
at PolylineGeometry.createGeometry (https://sandcastle.cesium.com/CesiumUnminified/Workers/createPolylineGeometry.js:389:21)
at createPolylineGeometry (https://sandcastle.cesium.com/CesiumUnminified/Workers/createPolylineGeometry.js:523:13)
at createGeometry (https://sandcastle.cesium.com/CesiumUnminified/Workers/createGeometry.js:60:21)
at callAndWrap (https://sandcastle.cesium.com/CesiumUnminified/Workers/createTaskProcessorWorker.js:61:17)
at Anonymous function (https://sandcastle.cesium.com/CesiumUnminified/Workers/createTaskProcessorWorker.js:106:17)

The example just loads one simple GeoJSON Feature of type LineString. If I change any of the three coordinates slighty, it works

geojson_produces_error = {"type":"Feature","geometry":{"type":"LineString","coordinates":[[7.970063350393387,47.59408093341338,773.65],[7.970063350393387,47.59408093341338,765.55]]}};
geojson_this_works     = {"type":"Feature","geometry":{"type":"LineString","coordinates":[[7.970063350393387,47.59408093341338,773.650001],[7.970063350393387,47.59408093341338,765.55]]}};

Sandcastle example:

Browsers:
Google Chrome Version 80.0.3987.163
Firefox 75.0 (64-Bit)
Internet Explorer 11.719.18362.0

Operating System:
Windows 10

[OmarShehata]

I initially thought this was related to this crash which happens when you have lines that are perfectly straight (sometimes): #8464 but it looks like this issue is specific to vertical lines. Here's a Sandcastle that loads the following GeoJSON:

The first two points are exactly vertical. If you remove the last point, it crashes.

[OmarShehata]

Also reported here with some additional debugging notes: #8974

[TJKoury]

@OmarShehata This could be related to calculating the number of points in a rhumb line; if you have two points in a polyline that differ only in altitude, then the radians distance squared tends to be zero.

For this particular case making a change will fix the issue.
[Core/PolyLinePipeline.js#L28]:(https://github.com/CesiumGS/cesium/blob/master/Source/Core/PolylinePipeline.js#L28)

return Math.max(
    1,
    Math.ceil(Math.sqrt(radiansDistanceSquared / (granularity * granularity))));

I have not tested this for other side effects.