Technically they could put a GPS chip in the ball which would calculate initial velocity and final velocity over start and finish position. This could trigger a heat sensor in the ball which if forward, this would make the rugby ball too hot to handle and the receiver would drop the ball. This converts a forward pass into a knock on which the ref and video ref can confirm.........easy.

Apart from the fact that one decision is based on the absolute position of the players and the ball and the other is based on the relative position of the players and the ball, you are right, they are exactly the same

Good quality ones are. They use them in geology to measure land movement of millimetres over long periods of time.

No I said the system you proposed wouldnt be possible. To avoid confusion i mentioned Hawkeye the company, not hawkeye the system.

Even for you Smokey, that's a poor attempt to wriggle out of something you've said!

Its not really complex to say there may be an engineering solution for accurate judgement of forward passes, but your's wasnt it.