Check user is following the route or not (iphone)

Question

i am making an navigation based application. In this application i am drawing a route from points selected by the user. I have requirement of recalculating route if user is

Answer 1

For each pair of points in each step, you can calculate the distance between them using the Pythagorean Theorem:

distance = sqrt(  pow((point1.x - point2.x), 2)   +   pow((point1.y - point2.y), 2)  )

Then, if the distance is greater than 100m, add intermediary points along the line segment.