Greg Esres wrote:



I can buy the idea of a relayed vector, but the person who provided
the vector still must see you on radar.

Yes, they have to be able to see you by a certain point after departure
to be allowed to issue vectors in the takeoff clearance.


When the aircraft is sitting
on the ground, approach control can't see it and therefore can't
vector it.

Well we can see aircraft on the ground, though that has nothing to do
with anything.




Consider that if you take off with the heading and start to wander
into some obstacle, tower won't be able to do anything about it
(because they won't know) and neither will the approach control until
they get you on radar, which will happen at various altitudes,
depending on where you're departing from.

In order to get a vector off the ground you have to be seen by the radar
facility within a half mile of the airport. So you can't wander into
anything.