T mid = -inner_product(ray.get_direction(), ray.get_start());
LinAl::Vector<T, D> nearest = ray.get_start()+ray.get_direction()*mid;
T offset_sq = radius*radius-inner_product(nearest, nearest);
T mid = -inner_product(ray.get_direction(), ray.get_start());
LinAl::Vector<T, D> nearest = ray.get_start()+ray.get_direction()*mid;
T offset_sq = radius*radius-inner_product(nearest, nearest);