it doesn't. most likely, it does the opposite--the display device (cybereyes, smartgoggles, whatever) accept not only trajectory information from the firearm, but gyroscopic positioning data that tells the display device where the gun is and what direction it's pointing in relation to the display device itself. the display device then collates all that data and uses it to create a visual aid that tells the user where his gun's bullets are going to go. just as in non-smartlinked shooting, the gun doesn't need to know where your eyes are, your eyes need to know where the gun is.

Well, in earlier editions of SR Smartlink was a .5 Essence neural implant that actually contained a specialized simrig in order to factor in the user's eye and weapon arm alignment thus calculating from three sets of targetting data (gun, eye, arm).
A non-implanted variant was available but was less effective (-1 TN bonus instead of -2).

As this external variant already existed I'd guess by 2070 the Smartlink technology has been advanced and calculating the targetting points with only two sets of reference data has been perfected:
The POV of the gun is compared to the POV of the Smartlink system (that most likely contains some kind of tiny camera itself).
This should work best with an implant or contact lenses as they move with the eye while glasses or helmet visors only move with the whole head...

I believe it is stated somewhere in the books that GPS doesn't work accurately indoors. The Orientation System from Augmentation is needed for this kind of accuracy, which is not a standard feature of a Smartlink.

...if memory serves me, the old arcade version of Battlezone had a similar feature which indicated which direction the enemy tank was when he wasn't in your sights. It didn't give distance though there was a small radar display at the top centre of the viewscreen. For it's day (1980) this was a fairly sophisticated game even though it was simple "green screen" (with overlay) vector line graphics. The US army actually used a version of the game to train soldiers for the Bradley AFV.

regardless of whether GPS is that accurate, magnetic orientation certainly isn't--and can't be. the magnetic north pole can move as much as 80km in a single day; it's impossible to get centimeter (much less millimeter) resolution off geomagnetism. i wouldn't even think meter resolution would be reliably possible.

another thing that occurs to me is that your solution requires the smartlink to know what you want to shoot at. i've never seen that mentioned in any canon description of the technology, and i don't think it could be done at all without DNI (meaning non-implanted smartlinks would require completely different technology).

and overall, really, it's like going around your elbow to get to your thumb. there's no real need to link smartlink technology to GPS technology; it's much easier to make it self-contained, and linking it to GPS opens up a lot of weaknesses that smartlinks wouldn't otherwise have. for instance, using GPS means you're constantly broadcasting your targeting information. that can reveal your location to the enemy, via triangulation, and of course anybody who can decrypt it will know who you're trying to shoot at. plus, as i mentioned above, it means your smartlink can be jammed.

it's a pretty shiny idea, but i don't think it's the best explanation for smartlink technology.

I think I've just come up with a new Pistols skill specialisation - Smartlink.

Going with the targetting directions idea (which apparently I've ripped off from an eighties arcade game - KK. ), once targets were identified, you wouldn't actually need an image of them in order to fire. SR2070's technology is certainly capable of keeping track of mobile targets. I'm picturing a system whereby all the person has to do is following the tracking pointers with their arm and pull the trigger when the icon flashes red. You would only have to train yourself in the counter-intuitive habit of moving your arm according to directions on a screen, but I'm sure this skill could be acquired quickly and come to the point where it's almost a reflex. The only thing that would limit your aiming would be identifying the targets and the awkwardness of firing at odd angles.

But the image of this is perfect. I can see a Samurai entering a room or lurking in the shadows, looking at each opponent in there and mentally flagging them as targets to his smart-link system. She then walks through the room never turning aside, whilst rapidly shooting people in all directions without looking. Maybe we're talking the betaware systems here, but it's certainly comfortably in SR2070 technology's ability. I'm surprised we didn't see some sort of tactical computer in Augmentation, but presumably there'll be something like it in Arsenal. Which ought to be out soon, I hope.

The Image Link is the Output to the User, the Smart Link device is the AR Input device. That's why you pay for this separate input device as a separate system. Instead of AR gloves, it's an AR SmartGun system.

Since I've never seen one in real life, please describe exactly what action by the user is detected and recognized by the device. I know that a keyboard triggers on fingers pressing keys, I am familiar with devices that trigger on sound produced by the vocal cords, and I'm aware of devices that track motions of the eyeball. In each case, a muscle (or set of muscles) in the human body is contracting and producing motion that the device takes as input. What exactly is the motion that a smartlink recognizes as "when this input happens, eject the clip"?

Even if RAW failed to mention that GPS doesn't work indoors... in real life, and in any fantasy world in which radio signals work the same as real life, a GPS only works when it can pick up signals from GPS satellites. Cloud cover, tree branches, etc. can reduce accuracy or completely block signals.

If smartlink always involves the glasses/goggles/etc including visual sensors, then that's relevant; sure, most people who buy smartlinks are also getting glasses/goggles that have camera-type devices, eg image recorder, vis mag, vis enhance, etc., but not necessarily. And as has been pointed out, a sensor on glasses doesn't match the user's field of vision unless they're always looking straight ahead (and no normal human always does so).

It looks to me as if someone writing for SR3 had a specific concept of how it works, involving interaction with the user's central nervous system, and someone copying material into SR4 only knew or cared about the cost and the functions.

Specialization for smartlink makes sense to me, and seems balanced enough in a street-level campaign, since if you lose your main gun and have to pick up another gun, the odds of it not being smartlinked are generally comparable to it not being a revolver, not being a slivergun, or other typical specialization. In a higher-end campaign, most guns you encounter will have smartlink.

That is way too simple and makes far too much sense.

DNI exists IRL. Not, of course, at the level of a Shadowrun datajack, but surgically implanting wires into people's central nervous system to sense activity in specific areas of the brain, and to stimulate specific areas of the brain, has been in progress since at least the 1980s. I imagine a datajack as a very, very complex and intrusive system of microwires implanted into frontal cortex, a processor to sort out the signals, and a literal jack like a phone jack (or ethernet or FireWire) probably behind the ear. If the smartlink system plugs into *that*, or an induction-based equivalent (trodenet), then of course it can correlate the image from the gun with the image from the eyes, because it has access to both.

But as written, you can just put on specially modified glasses, and if the glasses have microcameras to track your eye motion, that's not clear from the rules; it's only clear that the glasses have extra fancy capacities to overlay the HUD onto the user's field of vision.

I like your idea. It would have to be a little more tricky to avoid inadvertent clip ejection when a sudden noise causes a reflexive glance in that particular direction, but that's doable.

I think it is going to require a bit more then just glancing in the direction of the icon.

But, since the smartlink is quite a large modifier (costing a whoping 3 capacity or 6 avalibility on glasses) it can be assumed that you are paying for a system that is capable of telling where you are looking, and something that allows your eye movements to trigger the gun (perhaps something as simple as two quick blinks to fire the gun, or as complex as two left winks, a right wink, two blinks, and then another left wink). I mean, a simple image link can display virtually anything you want it to, and since it can overlay AR onto your vision (and over particular objects), it must have some means of telling where you are looking. It is quite likely that a small eye motion detector is standard on -all- eyeware. This also requires the glasses themselves to somehow know where they are looking, so this must also be a standard feature of all eyeware. Thus, if your glasses or whatever can tell where they are facing, spesificly where your eye is looking, and where your gun is held in relation, and where your gun's smartgun camera is looking, then smartgun can happen. The other possibility is that all eyeware comes with a small camera that can't record anything, but is used soly to tell where you are looking. It matches this up with the image captured by the smartgun camera, and thus can provide your overlay. Where your eyes are looking is irrelevent except to possably activate features (like auto-eject).

I suppose the end point is that given another 62 or so years, I'm sure that we can come up with the technology to make this sort of thing possable, and although I don't know for sure how it works, that doesn't mean it can't work. Also, once again, keep in mind that you've got a fairly big investment in the smartlink, so it makes sense that that investment is the stuff required to do all this cool stuff for you.

Ok, that is poorly spaced and whatnot, sorry about that everyone. I know I rambled a bit as well.

That's my ruling as well.