通过两个坐标点计算方向(dart 版本)

stackoverflow 看到 JS 版本的实现

https://stackoverflow.com/questions/8502795/get-direction-compass-with-two-longitude-latitude-points

//example obj data containing lat and lng points
//stop location - the radii end point
endpoint.lat = 44.9631;
endpoint.lng = -93.2492;

//bus location from the southeast - the circle center
startpoint.lat = 44.95517;
startpoint.lng = -93.2427;

function vehicleBearing(endpoint, startpoint) {
    endpoint.lat = x1;
    endpoint.lng = y1;
    startpoint.lat = x2;
    startpoint.lng = y2;

    var radians = getAtan2((y1 - y2), (x1 - x2));

    function getAtan2(y, x) {
        return Math.atan2(y, x);
    };

    var compassReading = radians * (180 / Math.PI);

    var coordNames = ["N", "NE", "E", "SE", "S", "SW", "W", "NW", "N"];
    var coordIndex = Math.round(compassReading / 45);
    if (coordIndex < 0) {
        coordIndex = coordIndex + 8
    };

    return coordNames[coordIndex]; // returns the coordinate value
}

翻译成 Dart

import 'dart:math';

void main() {
  String direction = vehicleBearing(39,116, 40, 116);
  print(direction);
}

String vehicleBearing (double start_lat, double start_lng, double end_lat, double end_lng) {
  double radians = atan2((end_lng - start_lng), (end_lat - start_lat));
  double compassReading = radians * (180 / pi);
  List<String> coordNames = ["N", "NE", "E", "SE", "S", "SW", "W", "NW", "N"];
  int coordIndex = (compassReading / 45).round();
  if (coordIndex < 0) {
    coordIndex = coordIndex + 8;
  };
  
  return coordNames[coordIndex];
}

如果需要输出中文，修改方向列表即可

["北", "东北", "东", "东南","南","西南","西","西北","北"];