If you know your location, and the intersection point it would just be the distance forumla again distance(intersection.x,intersection.y,you.x,you.y)
If what you're saying is that you want a height value for any arbitrary point on the line. You could use lerp, and the gett function of the math plugin so it'd be
If greenx and redx are equal, you'd use y values.
If you're one of those plugin shy people, the formula for math.gett is just