How to pickPosition on 3dtile set

Hi,everybody.when i pickposition on 3dtile set ,the position height always higher or lower than the turth height of the tile set feature,maybe caused by the camera posiontion. I want get the 3d tile set feature's height ,How can i do that. tahnks

Is this the same problem you’re seeing: https://www.youtube.com/watch?v=9twwwMHbjKU&feature=youtu.be ?

Linked from https://github.com/AnalyticalGraphicsInc/cesium/issues/4368