RTP and PDEPTH PROCESSINGS

hello
please I am a Geosoft beginner
I will like to know first which type of elevation data is required for RTP processing, I am a little bit confused whether it is the flight elevation or terrain elevation relative to sea level
Besides, when we want to generate Werner solutions in pdepth operator I wish to know what do "elevetion channel and topography" really stand for.
I am sincerly confused with this
best regards