I discussed this in Github, but I am trying to escalate this to someone that can answer me.
The SoftFilter that is still used in the latest version of ros_astra_camera has not been released and it can be found only in binary version on orbbec/OpenNI2 repository.
Can someone from Orbbec please tell us if:
1) The source code of the filter will be released.
2) What the filter is actually doing, to check if a better implementation can be used or not