CZML can't reference position with intervals

[emackey]

If one entity has a composite position (a position using time intervals), and another entity attempts to reference that position, the render loop throws. Here's some CZML:

[
  {
    "id":"document",
    "version":"1.0",
    "clock":{
      "interval":"2017-01-05T11:00:00Z/2017-01-05T11:59:59Z",
      "currentTime":"2017-01-05T11:29:59.5Z",
      "multiplier":60,
      "range":"LOOP_STOP"
    }
  },
  {
    "id":"Test Reference Object",
    "availability":"2017-01-05T11:00:00Z/2017-01-05T11:59:59Z",
    "name":"Test Reference Object",
    "path":{
      "show":true,
      "width":2,
      "resolution":300,
      "leadTime":0,
      "trailTime":172800,
      "material":{
        "solidColor":{
          "color":{
            "rgba":[
              255,255,0,255
            ]
          }
        }
      }
    },
    "position":{
      "reference":"Test Main Object#position"
    }
  },
  {
    "id":"Test Main Object",
    "availability":"2017-01-05T11:00:00Z/2017-01-05T11:59:59Z",
    "name":"Test Main Object",
    "label":{
      "text":"Test Main Object",
      "font":"bold 32px \"Droid Sans\",sans-serif",
      "style":"FILL_AND_OUTLINE",
      "scale":0.5,
      "pixelOffset":{
        "cartesian2":[
          5,0
        ]
      },
      "horizontalOrigin":"LEFT",
      "verticalOrigin":"CENTER",
      "fillColor":{
        "rgba":[
          255,255,0,255
        ]
      },
      "outlineColor":{
        "rgba":[
          0,0,0,255
        ]
      },
      "outlineWidth":2.4
    },
    "point":{
      "pixelSize":7,
      "color":{
        "rgba":[
          255,255,0,255
        ]
      }
    },
    "position":[
      {
        "interval":"2017-01-05T11:00:00Z/2017-01-05T11:59:59Z",
        "interpolationAlgorithm":"LAGRANGE",
        "interpolationDegree":5,
        "referenceFrame":"INERTIAL",
        "epoch":"2017-01-05T11:00:00Z",
        "cartesian":[
          0,10775966.0,-40747218.0,-86707.0,
          3599,20984737.0,-36550703.0,-135028.0
        ]
      }
    ]
  }
]

The error thrown is:

TypeError: Cannot read property 'length' of undefined
    at subSampleCompositeProperty (http://c1200610-00.stk.com/Cesium/Source/DataSources/PathVisualizer.js:208:38)
    at reallySubSample (http://c1200610-00.stk.com/Cesium/Source/DataSources/PathVisualizer.js:246:21)
    at subSample (http://c1200610-00.stk.com/Cesium/Source/DataSources/PathVisualizer.js:263:22)
    at PolylineUpdater.updateObject (http://c1200610-00.stk.com/Cesium/Source/DataSources/PathVisualizer.js:369:30)
    at PathVisualizer.update (http://c1200610-00.stk.com/Cesium/Source/DataSources/PathVisualizer.js:472:32)
    at DataSourceDisplay.update (http://c1200610-00.stk.com/Cesium/Source/DataSources/DataSourceDisplay.js:260:41)
    at Viewer._onTick (http://c1200610-00.stk.com/Cesium/Source/Widgets/Viewer/Viewer.js:1483:49)
    at Event.raiseEvent (http://c1200610-00.stk.com/Cesium/Source/Core/Event.js:147:30)
    at Clock.tick (http://c1200610-00.stk.com/Cesium/Source/Core/Clock.js:309:21)
    at CesiumWidget.render (http://c1200610-00.stk.com/Cesium/Source/Widgets/CesiumWidget/CesiumWidget.js:681:43)

To work around this, copy the position block from the main entity above, and replace the position reference in the other entity with a copy-and-paste of the main position block. Then the CZML will work fine. But, there's no easy way to tell the STK Components CZML writer to use this workaround.

[emackey]

From my point of view at least, this is a priority 😄

[mramato]

The fix for this should be trivial, the problem is in reallySubSample in PathVisualizer.js, it unwraps the inner property but then tries to sample the ReferneceProperty instead of the unwrapped property. However, there are dragons here and I found at least 2 other path bugs (one is kind of tricky) while looking at this. I'll see what I can do.