【No.004】2点間の緯度経度の方位は？大量の変換に対応しているツールも限定展開！

<label>点1の緯度y1（10進）:</label>
<input type="text" id="lat1" value="36.1234">
<label>点1の経度x1（10進）:</label>
<input type="text" id="lon1" value="136.2468">
<br>
<label>点2の緯度y2（10進）:</label>
<input type="text" id="lat2" value="36.6789">
<label>点2の経度x2（10進）:</label>
<input type="text" id="lon2" value="136.1357">
<br>
<button type="button" onclick="calculateBearing()">方位を計算する</button>
<div id="result"></div>

<script>
function calculateBearing() {
  const lat1 = parseFloat(document.getElementById("lat1").value);
  const lon1 = parseFloat(document.getElementById("lon1").value);
  const lat2 = parseFloat(document.getElementById("lat2").value);
  const lon2 = parseFloat(document.getElementById("lon2").value);

  const lat1Rad = lat1 * (Math.PI / 180);
  const lon1Rad = lon1 * (Math.PI / 180);
  const lat2Rad = lat2 * (Math.PI / 180);
  const lon2Rad = lon2 * (Math.PI / 180);

  const y = Math.sin(lon2Rad - lon1Rad) * Math.cos(lat2Rad);
  const x = Math.cos(lat1Rad) * Math.sin(lat2Rad) -
            Math.sin(lat1Rad) * Math.cos(lat2Rad) * Math.cos(lon2Rad - lon1Rad);

  let bearing = Math.atan2(y, x);
  bearing = bearing * (180 / Math.PI);
  bearing = (bearing + 360) % 360;

  document.getElementById("result").innerHTML = "方位は " + bearing.toFixed(2) + " ° です。";
}
</script>