Is there a way to instruct the Phantom 4 Pro to return to home via a specific waypoint?
(e.g. let's say going home from where I'm flying would go directly over a crowd of people, can I somehow tell it to return to home by following the way it got where it was going, or by going to a waypoint before coming home?)

Have a look at page 15 of the P4P manual under 'Failsafe RTH', it would appear it retraces the route it took to get to the point where RTH is initiated.

http://www.dji.com/phantom-4-pro/info#downloads

Short of flying it yourself, no.

Aardvark Posted at 2017-8-10 16:25
Have a look at page 15 of the P4P manual under 'Failsafe RTH', it would appear it retraces the route it took to get to the point where RTH is initiated.

http://www.dji.com/phantom-4-pro/info#downloads

Failsafe!  Thank-you.  I knew I read it somewhere but coudn't recall what it was called.

mhoppes Posted at 2017-8-10 17:38
Failsafe!  Thank-you.  I knew I read it somewhere but coudn't recall what it was called.

It only retraces for a short time until it regains signal.
It's not going to retrace all the way home.

Labroides Posted at 2017-8-10 17:46
It only retraces for a short time until it regains signal.
It's not going to retrace all the way home.

You could always switch off RC, would that not then force a full RTH retrace ?

mhoppes Posted at 2017-8-10 17:38
Failsafe!  Thank-you.  I knew I read it somewhere but coudn't recall what it was called.

Not quite sure if it could be considered 'failsafe' though certainly much less likely to fail than the  previous 'shortest route home' (straight line) version.
Many have previously lost their pride and joy after pushing RTH, better to fly home manually in View if you can.

Aardvark Posted at 2017-8-11 00:35
You could always switch off RC, would that not then force a full RTH retrace ?

No.  The manual is pretty sketchy about how far it will retrace but the Phantom can't store a full map for a long path and when you lose signal, because you fly behind an obstacle, just coming back a short way is usually enough to reconnect

Here's what the manual says: The Forward Vision System allows the aircraft to create a real-time map of its flight route as it flies.
If the Home Point was successfully recorded and the compass is functioning  normally,  Failsafe  RTH  will  be  automatically  activated  if  the remote controller signal is lost for more than three seconds.  The aircraft will plan its return route and retrace its original flight route home. The aircraft will hover for 10 seconds at its current location.  When it regains signal connection it will wait for pilot commands.  The  Return-to-Home process may be interrupted and the pilot given control of the aircraft if the remote controller signal connection is re-established

Labroides Posted at 2017-8-11 00:54
No.  The manual is pretty sketchy about how far it will retrace but the Phantom can't store a full map for a long path and when you lose signal, because you fly behind an obstacle, just coming back a short way is usually enough to reconnect

Here's what the manual says:  The Forward Vision System allows the aircraft to create a real-time map of its flight route as it flies.

It would be an interesting one to test out in an open area, fly an elaborate route, not necessarily far from home point. And see if it replicates that on RC power off. Or does it use AI  to take it to the last known  point where it can then fly a straight course back to conserve battery ?

Aardvark Posted at 2017-8-11 01:13
It would be an interesting one to test out in an open area, fly an elaborate route, not necessarily far from home point. And see if it replicates that on RC power off. Or does it use AI  to take it to the last known  point where it can then fly a straight course back to conserve battery ?

It goes back for a short time.
I can't remember if it's 10 secs or 30 secs but something like that.
Then it does the normal RTH if signal is not reconnected.
Normally on loss of signal, just moving backwards 10 metres or so should restore signal.

Yes, a good thing to test out in the open to work out what's happening.

As Labroides mentioned, the drone will retrace until it receives the signal. Once re-connected, you can control it again. Also, I would not suggest to turn off the RC to test this feature as it might be dangerous.

SInce the flight route is saved (and can be seen and replayed in the Flight Records along with GPS cohordinates) in theory it should be possible for DJI to add a feature that actually flies the aircraft on the reverse path... Just don't know how complex it would be.