Hey folks,
last few weeks I've been flying in a gully surrounded by trees.  The gps signal comes and goes and the behaviour of the p4 is erratic.  Especially as the signal comes and goes.  It bobs up and down, sometimes meaning I have to fully pull the left stick down to maintain position (and it cant be the wind, its been dead still).

Is there a mode, other that atti, that switches off the gps, but uses the gyro to try to maintain position? (I guess I'm asking for tripod mode, without the GPS!).

Why not ATTI? I fly my P4P in my church's gym occasionally and do it in ATTI (metal building), never had a problem.  The only issue I have is with my Mavic Air, it can't be put in ATTI mode manually so when I get close to an exterior wall and GPS starts bouncing in and out, the Air gets a little wonky. Easy solution, I don't fly close to an exterior wall.

atti mode switches off obstacle avoidance.  In a gully is not inside, there is still shifting air currents and crap loads of branches.

Flying a drone without solid GPS lock is always risky, no matter what. Tripod mode seems to be the best option in your scenario since gains are trimmed down significantly. Therefore if GPS is lost for a while and drone enters ATTI mode automatically, she has relatively low momentum to deal with and to compensate with sticks. Practice ATTI flying first in open field and in different wind conditions to get the feel, baby steps approach. Be aware of small, hard to see branches above when finally flying in your hole. Props may suck them down when too close, with obvious outcome. Good luck!

ok thanks, so are they my only 2 options: atti, or no atti? Isnt there an option for atti + obstacle avoidance?

When you are flying and it loses GPS, that is in effect ATTI mode, the good thing about ATTI opposed to losing GPS is then its height is not effected, only the horizontal, i.e. drifting, but if there is no wind then there should be little drift, if any? (not sure there) If i was you, i would fly ATTI from the get go, and use very tiny stick movements, just remember that there is no braking when you let go of the sticks, you have to pull back (reverse thrusters) to brake. But from the initial it sounds like you are not keen on ATTI, perhaps it would be prudent to practise 1st in the open, you can always flick the switch back to GPS if there is an issue, i.e. gonna crash

gherk Posted at 2018-3-22 16:57
ok thanks, so are they my only 2 options: atti, or no atti? Isnt there an option for atti + obstacle avoidance?

Obstacle avoidance won't work without GPS.
The other mode you are looking for is P-opti which can use the VPS to hold position but only:
1.  Within VPS range - altitude 1-10 metres
2.  In good lighting (not deep shadow)
3.  If the ground surface has a distinct pattern or texture (not plain concrete, grass etc.)

Labroides Posted at 2018-3-22 21:07
Obstacle avoidance won't work without GPS.
The other mode you are looking for is P-opti which can use the VPS to hold position but only:
1.  Within VPS range - altitude 1-10 metres

yes that sounds good, exactly where I'll be flying.  Not sure how it will handle flying over water though, eeek

It is not recommended to fly when GPS is not available as flying in ATTI mode requires high skills. You may practice in Simulator in advance.

gherk Posted at 2018-3-22 22:23
yes that sounds good, exactly where I'll be flying.  Not sure how it will handle flying over water though, eeek

Not sure how it will handle flying over water though
Water is terrible for VPS, there's no  distinct pattern or texture for it to lock on to.

gherk Posted at 2018-3-22 22:23
yes that sounds good, exactly where I'll be flying.  Not sure how it will handle flying over water though, eeek

"In a gully is not inside, there is still shifting air currents and crap loads of branches. "

Can I suggest that you switch on manual Object Avoidance, in other words you the pilot decides that the risks of the aircraft colliding with another object are high and chooses not to fly there.