I don't know what is a control point, but if you press the Up arrow key, you have constraint on the Z axis If you want draw only vertical lines, you can use the Chris Fullmer plug "3 lines tools" by lenght by elevation line on normal

@unknownuser said: You could setup different scenes that have the axis set differently in each scene. If you uncheck all the options for each scene but the model axis, your scene buttons will do nothing except change the model axis. Interesting use of scenes - nota benissima

Thx i did go through it,just didnt get it at first,ive done it on my work pc but this old horse does not seem to support,will have to try at home.