如何在html5 / ionic中使用平方米或平方公里

Question

这就是我的想法。我想用GPS获取用户位置。我没有发送当前位置，而是想计算平方公里或米。

----------------------------------
|                                |
|                                |
|                                | 
|                                |
|              .                 |
|              ^                 |
|      My current position       |
|                                |
|                                |
|                                |
----------------------------------

正如您在上图中所看到的，我现在的位置，但我想计算HTML5或Ionic周围的整个区域将更受欢迎。

更新

在上图中，红点是我的位置，我需要将整个区域放在红色矩形中。获取数据库中的那个商店。我查看了多边形区域公式，但这需要几个顶点，地理位置我只获得经度和纬度两个坐标。我怎么用这两点来做到这一点？

更新

我找到了解决方案here，但此解决方案是继续跟踪用户的当前位置，并且在calculateDistance函数中公式使用当前位置（经度和纬度）和跟踪位置（经度和纬度），即{ {1}}

这对我的第二个场景非常好，但首先我不想跟踪用户的位置。首先，我简单地获取当前用户位置（经度和纬度），从中计算区域并将其发送到服务器。现在我不确定我将如何实现这一目标。有什么帮助吗？

Answer 1

I've created a circle in google maps and then got his bounds, which return a square bounding boxes.

function getBounds(latLng, radius) {
  /*
  * Params:
  *     latLng: google maps LatLng object or object literal  // example: { lat: -34.397, lng: 150.644 }
  *     radius: Number(int) in Miters. For example 1000 will be 1 sq Kilometer
  * Returns:
  *     object literal in the following format:
  *         {
                northEast: {
                  lat: (float),
                  lng: (float),
                },
                southWest: {
                  lat: (float),
                  lng: (float),
                },
            }
  * */

  const circle = new google.maps.Circle({
    center: latLng,
    radius: radius
  });
  const bounds = circle.getBounds();
  const northEast = bounds.getNorthEast();
  const southWest = bounds.getSouthWest();
  return {
    northEast: {
      lat: northEast.lat(),
      lng: northEast.lng(),
    },
    southWest: {
      lat: southWest.lat(),
      lng: southWest.lng(),
    },
  };
}

I took the library to add a short snippet for you to see if this is the right answer for what you were looking for. Once you click on the map you will see a marker and the triangle around it.

Note: Please copy the code and add your google map API key. Without your API key, the map will fail to load.

let map;
let marker;
let rectangle;

function initMap() {
  const latLng = {
    lat: -34.397,
    lng: 150.644
  };
  const radius = 1000;
  map = new google.maps.Map(document.getElementById('map'), {
    center: latLng,
    zoom: 11,
  });
  google.maps.event.addListener(map, 'click', function(event) {
    const location = event.latLng;
    const bounds = getBounds(location, 1000);
    console.log(bounds);
    addRectangle(bounds);
    addMarker(location);
  });
}

function addMarker(location) {
  if (marker) {
    marker.setMap(null);
  }
  marker = new google.maps.Marker({
    position: location,
    map: map,
  });
}

function addRectangle(bounds) {
  if (rectangle) {
    rectangle.setMap(null);
  }
  rectangle = new google.maps.Rectangle({
    strokeColor: '#FF0000',
    strokeOpacity: 0.8,
    strokeWeight: 2,
    fillColor: '#FF0000',
    fillOpacity: 0.35,
    map: map,
    bounds: {
      north: bounds.northEast.lat,
      south: bounds.southWest.lat,
      east: bounds.northEast.lng,
      west: bounds.southWest.lng,
    },
  });
}

function getBounds(latLng, radius) {
  /*
  * Params:
  *     latLng: google maps LatLng object or object literal  // example: { lat: -34.397, lng: 150.644 }
  *     radius: Number(int) in Miters. For example 1000 will be 1 sq Kilometer
  * Returns:
  *     object literal in the following format:
  *         {
                northEast: {
                  lat: (float),
                  lng: (float),
                },
                southWest: {
                  lat: (float),
                  lng: (float),
                },
            }
  * */

  const circle = new google.maps.Circle({
    center: latLng,
    radius: radius
  });
  const bounds = circle.getBounds();
  const northEast = bounds.getNorthEast();
  const southWest = bounds.getSouthWest();
  return {
    northEast: {
      lat: northEast.lat(),
      lng: northEast.lng(),
    },
    southWest: {
      lat: southWest.lat(),
      lng: southWest.lng(),
    },
  };
}

/* Always set the map height explicitly to define the size of the div
         * element that contains the map. */

#map {
  height: 100%;
}


/* Optional: Makes the sample page fill the window. */

html,
body {
  height: 100%;
  margin: 0;
  padding: 0;
}

<script src="https://maps.googleapis.com/maps/api/js?callback=initMap" async defer></script>
<div id="map"></div>

Answer 2

这是一个函数（使用ES6），它采用方形的平方公里的纬度，经度和面积，并返回一个对象，该对象包含以该位置为中心的四边形（两个纬度和两个经度）。

function getBoundaries(lat, lon, area) {
  // angle conversions
  const toRad = t => t * Math.PI / 180;
  const toDeg = t => t * 180 / Math.PI;

  // radius of the Earth (km)
  const radius = 6371;

  // calculate distance to the sides of the square
  const dist = Math.sqrt(area)/2;

  // calculate change in coordinates
  const dLat = toDeg(dist / (radius * Math.cos(toRad(lon))));
  const dLon = toDeg(dist / radius);

  return {
    north: lat + dLat,
    south: lat - dLat,
    east: lon + dLon,
    west: lon - dLon
  }
}

例如，如果你想要一个面积为10平方公里的正方形，居中于40°N 74°W，那么你的正方形将是

const square = getBoundaries(40, -74, 10);
// {north: 40.051587793956195, south: 39.948412206043805, east: -73.98578047688149, west: -74.01421952311851}