from __future__ import annotations

import math


def fresnel_radius_m(d1_m: float, d2_m: float, d_total_m: float, freq_mhz: float) -> float:
  if d_total_m <= 0 or freq_mhz <= 0:
    return 0.0
  f_ghz = freq_mhz / 1000.0
  return 17.3 * math.sqrt((d1_m * d2_m) / (f_ghz * d_total_m))


def clearance_m(
  los_height_m: float,
  total_height_m: float,
  fresnel_radius_m: float,
  fresnel_factor: float,
) -> float:
  return los_height_m - total_height_m - fresnel_radius_m * fresnel_factor