Cannon rotation on that one _is_ electric (some are hydraulic), but it has a 360deg rotation so there's no definite "stop" spot for each side.  The operator has to judge when it's sideways every time, so any kind of contact for automatic detection would have to have quite a bit of runout.  Now that I think of it though, magnetic detectors are simple and a fellow could weld a couple of curved bits of pipe to raise the surface of the rotating tower so two "zones" with, say, a 5 or 10 degree hotspot could be detected as left or right by two magnets, but wind direction still controls where the chemical goes after the windblast from the fan loses its force.  The fan's pretty powerful (Cima says the fan on that one absorbs 55hp).  Chemicals are turned on by two electric solenoids, so they should be easy to input. 

 Good idea using the wind direction as chemical direction for, say, a contour pattern or whatever, but I never use those for mistblowing.  Personal preference and the KISS principle I guess.  It also might be a bit harder to define wind direction from the start as coming from, say, the right side of the tractor and at 90degrees to the line of travel if your first line isn't straight.  If the field isn't square (almost nothing I spray is) or if it is and the wind isn't blowing squarely in the direction of the shortest sides (small miracle, because I always spray travelling in the direction that gives me the most long straight lines while still travelling at 90deg to the wind) then I force a straight line pattern and either shut off the top cannon when I'm getting close to an edge or use only the top cannon if I'm trying to avoid something close to me that I've already sprayed.  It gets a little complicated if the field edges have curves and doglegs in them.

 Just think I've come up with a simpler idea to electrically define which side the cannon is shooting towards.  The electric solenoids for the chemical could be cloned, and the operator could flip the "left" switches when he's shooting to the left, and the "right" switches when he's shooting to the right and those lines could be used to toggle the dual implements like you did for that other fellow.  Either that or add a third manual toggle in the cab to tell the mapping system which direction the cannon's shooting towards.  Those still don't solve the problem of the mist always blowing downwind on a contoured pattern though.  Wind direction still should be input somehow, and is probably still the best way to define or select the implement shape after each turn.