The functionality you are describing is within Parking Assistant Professional. Don't think many cars yet been delivered with this functionality, so I'm afraid not many knows..
However, I think I read that the accuracy should be within 30cm.
My car only got Parking Assistant Plus, and the functionality of reversing out in the same track as i drove in is working very well. I would say its well within 30 cm.
Parking Assistant Professional is standard on all iX's (from a dealer document seen last year), Plus adds surround cameras, panorama view etc.
From a press release
The Parking Assistant Professional has been designed to provide
comfortable entry into and exit out of parking spaces in frequently
recurring situations. It can store up to ten manoeuvres with a total
length of up to 600 metres. This assistance is particularly helpful in
twisty courtyard entrances or tight parking situations where several
adjustments are required to guide the car into the space. Driving the
selected route manually just once with Parking Assistant Professional
activated is enough to store the GPS data and trajectories. The route
is then recognised as the vehicle approaches the starting point for the
manoeuvre. The driver can now hand over the driving task to the Parking
Assistant Professional, although they remain responsible for monitoring
Interesting that the i4 can store GPS coordinates to activate the Panorama camera view but the iX does not
Yet it can store a GPS position to lower the driver door window - how useful is that !
The feature mentioned is likely to be a software update
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