docs: def lonlat2xyz(lons, lats):
      """Convert lons and lats to cartesian coordinates."""
      R = 6370997.0
      x_coords = R * da.cos(da.deg2rad(lats)) * da.cos(da.deg2rad(lons))
      y_coords = R * da.cos(da.deg2rad(lats)) * da.sin(da.deg2rad(lons))
      z_coords = R * da.sin(da.deg2rad(lats))
      return x_coords, y_coords, z_coords