ReferenceValue not allowed in Interpolation?

According to , billboard#alignedAxis is interpolatable.

When I use

“alignedAxis”: [




with 1.36, the CZML is processed without problems. When I cnage one of the values to a velocityReference

“alignedAxis”: [




in order to align the billboard with the path for part of the track, the parser throws the error

“{“interval”:“2014-09-07T23:41:48Z/2014-09-07T23:44:45Z”,“velocityReference”:“Track-16638#position”} is not a valid CZML interval.”


“alignedAxis”: {

   "velocityReference": "Track-16638#position"


works as well without problems, but I need to have the billboard to be ‘Up-Aligned’ for part of the track.

Am I missing something, or is a reference value not allowed as an interpolated value?


I confirmed that “velocityReference” doesn’t work within an interval. This appears to be an error in the implementation and I will open an issue to correct this in the future.

To be clear, this is not related to interpolation, which approximates a continuous function from samples. Interval syntax defines a property as piecewise function of time.

To work around this problem in the code, you can use an extra level of indirection by using the existing “reference” syntax. For the interval of interest, the alignedAxis can be defined as a reference to another fake object’s alignedAxis, which itself can then be defined as the velocityReference value.

See this sandcastle example for a working demonstration.

Thanks, Scott - that did it!