static _computeUniqueEllipsoids(imageryLayers) {
    //>>includeStart('debug', pragmas.debug);
    Check.defined("imageryLayers", imageryLayers);
    //>>includeEnd('debug');

    const ellipsoidsSet = new Set();
    const length = imageryLayers.length;
    for (let i = 0; i < length; i++) {
      const imageryLayer = imageryLayers.get(i);
      const ellipsoid = ModelPrimitiveImagery._getEllipsoid(imageryLayer);
      ellipsoidsSet.add(ellipsoid);
    }
    return [...ellipsoidsSet];
  }
Computes an array containing the <i>unique</i> ellipsoids that
appear in the imagery layers of the given collection.

@param {ImageryLayerCollection} imageryLayers
@returns {Ellipsoid[]} The ellipsoids
@private