Use two points to generate a transform which will rotate one the start point to the angle of the second.

AffineTransformMakeFromPointToPoint.m

CGAffineTransform AffineTransformToPositionOnLines(const CGPoint points[],
                                                   size_t count,
                                                   CGFloat position,
                                                   BOOL rotate)
{
    CGAffineTransform transform = CGAffineTransformIdentity;
    
    if (count > 1)
    {
        for (size_t index = 0;index<count-1;index++)
        {
            CGFloat dx = points[index+1].x - points[index].x;
            CGFloat dy = points[index+1].y - points[index].y;
            CGFloat dh = hypot(dx, dy);
            if (position < dh)
            {
                CGFloat cosA = dx/dh;
                CGFloat sinA = dy/dh;
                
                transform = CGAffineTransformTranslate(transform, points[index].x, points[index].y);
                
                CGFloat fd = position / dh;
                
                transform = CGAffineTransformTranslate(transform, dx * fd, dy * fd);
                if (rotate)
                {
                    transform = CGAffineTransformConcat(CGAffineTransformMake(cosA, sinA, -sinA, cosA, 0, 0), transform);
                }
                break;
            }
            position -= dh;
        }
    }
    
    return transform;
}