I think this helps explains why its so good…
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This means the further apart the antennas are - precission increases?
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Does anyone use Dual around trees? Seems like an IMU would still be handy in those cases.
Also, it still seems bizarre to me that adding another device that deems its position from space & corrections can make a system MORE accurate than fusing with a device that is meant for pitch/roll and is 100& local to the machine.
Not saying Dual isn’t better because I haven’t tried it, but just thoughts 
Almost all my fields have woodland/forest borders.
So outside run on each field there’s heavy shading from trees, I’ve had no problems at all, it was the thing I was most concerned about.
I’m using the white survey type antennaes.
Imus all suffer from drift, interference and vibrations. Hence needing to fuse with GPS.
The only standalone IMU that will beat dual antennae is a Fibre optic gyroscope, but one will cost more than a new tractor!
I can try and drive under some tree canopy and see at one point I loose dual.
The tractor I posted a video of started as a single antenna with IMU. After a year and a half I went dual. Tuning is easier to get it to perform well. With a single antenna I could never completely tune out a faint weave of the front end as it tried to find the line. With dual the weave is gone, the tractor gets on line and runs arrow straight across the field
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To keep this thread updated, I’m still really pleased with how well Dual works, find it just drives really straight,
So as long as you can mount two antennae’s either side of the cab, I’d always opt for Dual. Drives really straight AB lines, steers better on curved lines and makes neater U Turns.
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I get duel antenna side by side give roll data, but duel antenna front back give better Yaw data, which would result in cleaner path data?
The system can have duel antenna and an IMU. So why not great yaw data and still use the IMU?
Yaw data is for anyone wondering heading and can see if the heading in on path or not, you put one antenna over the rear axil of the tractor this sets the centreline of the tractor the other as far forwards as you can to detect what the front of the tractor is doing. If it’s to the left or right or on the path?
So while we can use duel antenna to give better roll data is that the best use of duel antenna?
You will only get better heading accuracy mounting the Antennaes longitudinally if they can be spaced further apart than if mounted transversely.
That would usually mean mounting one on cab roof and mounting the other on the bonnet/hood, this will introduce all sorts of multipath errors and Antennaes seeing different satellites, not what you want with dual.
If you can mount the Antennaes transversely left and right of cab 1.5m or greater apart you will depending on gnss receiver(s) have an absolute heading accuracy around 0.1 degrees and absolute roll accuracy of <0.2
BNO085/TM171 have absolute roll accuracy of 1 degree. With a typical antennae height of 3m on a tractor cab roof that, the IMUs will have a 4.2 cm greater lateral error on the AB line than a Dual system.
I understand the theory associated with what you are asking. I will say in practice side by side dual antennas leave nothing on the table. My average cross track error is consistently measured in the tenths of an inch (2 cm or less)
Knowing the tractor is on unpredictable ground conditions and the system has to take positioning data and translate that in to a correction for the steering system, I don’t think any noticeable improvement could made to the current dual antenna system. It will run in the same tracks all day long. The picture I attached was of a field I strip tilled with a 4 row strip till bar. You can’t tell where the guess row is. It’s perfectly even all the way across the field.
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What dual and steering system is that
Dual F9P’s on an AIO 4.2 board. Steering is hydraulic, I used a Hydraforce valve, but if I ever set up another tractor I will probably just order a Baraki valve. (It works great now, but it took a few modifications to my original hydraulic steering set up to get it dialed in)