get _mappedPositionsNeedUpdate() {
    if (!defined(this._mappedPositionsPerEllipsoid)) {
      return true;
    }
    const model = this._model;
    const lastModelMatrix = this._mappedPositionsModelMatrix;
    if (!Matrix4.equals(model.modelMatrix, lastModelMatrix)) {
      return true;
    }
    return false;
  }
Returns whether the <code>MappedPositions</code> have to be
re-computed with <code>_computeMappedPositionsPerEllipsoid</code>.

This is <code>true</code> when the positions have not yet been
computed, or when the <code>modelMatrix</code> of the model
changed since the previous call.

@returns {boolean} Whether the mapped positions need an update
@private