... on the dummy vehicle proved to be flawed. By rolling the dummy vehicle over it, I found that on sharp reverse curves there were places where short sections of vehicle overlapped the drawn line by a fraction. To work properly, it would need lines drawn from an infinite number of points along the side of the vehicle. No doubt someone with a better geometrical head than mine could have predicted that. So back to the drawing board, and I have now drawn the full vehicle outline at frequent steps along the track: 2_270842_500000001.png Yellow shows the maximum extent anywhere of the area swept by vehicle body, the purple section shows the clearance allowance each side. Rolling the vehicle over it proves it to be correct, but it is not always the corners or mid-points of the body which create the extent, as I found earlier. On a reverse curve such as this S-transition, you get necks in the envelope which look as if they must be wrong, but on rolling the vehicle it proves to be correct. To get a ...