Thanks!
For the method I showed, only one plugin is needed+ - mc AlignEnds, and the native tools (Line, Move, Scale, Wireframe style).
+ If it is desired without any plugin, then AE can be replaced with the Move tool, and move each vertex on Z until the intersection with the terrain.
It is interesting and pleasant to work on landscape projects. 
Do you know what methods professionals in the field apply in this case? Do they have a faster, simpler, more efficient way of working this?
Thank you, mr Coolidge!