VAR is getting close to NFL territory now

Nobody can tell looking at the super slow motion replay what the decision will be.

The second Japan goal looked like the ball was fully across the end line before being crossed. The offside call on Croatia I had assumed was on a different player, because the graphic they showed looked inconclusive at best.

If the sensor is in the center of the ball, how do they tell when the ball is over the line? Are they assuming a standard width of the goal line? Is it possible the actual line drawn on the field does not match this width? Or is goal line technology vision system based and not sensor based?