Why are the covariance values for position so high in the Odometry message published by swiftnav_ros package (piksi multi RTK setup is being used, with succesful RTK fix.)

header: 
  seq: 420
  stamp: 
    secs: 1525036934
    nsecs: 533197224
  frame_id: "gps"
child_frame_id: ''
pose: 
  pose: 
    position: 
      x: 2.29
      y: 3.038
      z: -0.516
    orientation: 
      x: 0.0
      y: 0.0
      z: 0.0
      w: 0.0
  covariance: [100000000.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 100000000.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 484000000.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 1000.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 1000.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 1000.0]
twist: 
  twist: 
    linear: 
      x: -0.004
      y: 0.008
      z: 0.008
    angular: 
      x: 0.0
      y: 0.0
      z: 0.0
  covariance: [0.015210000000000001, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.015210000000000001, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.03198, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 1000.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 1000.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 1000.0]

Notice the values in the covariance in the position. I notice that in the driver, the covariance fields are populated as such:

// populate the pose covariance matrix if we have a good fix
double h_covariance = (sbp_ned.h_accuracy * sbp_ned.h_accuracy) / 1.0e-6;
double v_covariance = (sbp_ned.v_accuracy * sbp_ned.v_accuracy) / 1.0e-6;

// Pose x/y/z covariance 
rtk_odom_msg->pose.covariance[0]  = h_covariance;   // x = 0, 0 in the 6x6 cov matrix
rtk_odom_msg->pose.covariance[7]  = h_covariance;   // y = 1, 1
rtk_odom_msg->pose.covariance[14] = v_covariance;  // z = 2, 2

Why is there a division by 1.0e-6?