When taking off, my SOP is:

• Get props turning
• Press joystick forward to get a couple feet off the ground
• Hover in place until Home Point updated
• Fly
  

Works a-ok every time outdoors.
But when I attempt indoors, the craft will not hover in place upon takeoff.  Instead, it drifts in one direction or another until it hits something and does not respond properly to control input.
OTOH, i can take off outside and then fly into the same room where takeoff failed and maitain full control.
Would I be correct in assuming that this is something to do with GOS acquisition?

If there is no GPS the drone will enter ATTI mode, which you'll need to control the aircraft manually, the aircraft itself cannot precisely hover nor autonomous braking under this condition.  Needs GPS to fly stable like it does outside.