一種在地圖中處理曲線的通用方法

本文分享一種能夠用於處理曲線的算法，是本人在百度地圖開源庫基礎上改造的，能夠用於其餘地圖場景中處理點數據，只要兩個以上的點，就能夠獲得平滑的曲線。例如小程序，將處理後獲得的點賦值給polyline的points便可。

function getCurveByTwoPoints(obj1, obj2) {
    if (!obj1 || !obj2) {
        return null
    }
    var B1 = function (x) {
        return 1 - 2 * x + x * x
    };
    var B2 = function (x) {
        return 2 * x - 2 * x * x
    };
    var B3 = function (x) {
        return x * x
    };
    curveCoordinates = [];
    var count = 30;
    var isFuture = false;
    var t, h, h2, lat3, lng3, j, t2;
    var LnArray = [];
    var i = 0;
    var inc = 0;
    if (typeof(obj2) == "undefined") {
        if (typeof(curveCoordinates) != "undefined") {
            curveCoordinates = []
        }
        return
    }
    var lat1 = parseFloat(obj1.lat);
    var lat2 = parseFloat(obj2.lat);
    var lng1 = parseFloat(obj1.lng);
    var lng2 = parseFloat(obj2.lng);
    if (lng2 > lng1) {
        if (parseFloat(lng2 - lng1) > 180) {
            if (lng1 < 0) {
                lng1 = parseFloat(180 + 180 + lng1)
            }
        }
    }
    if (lng1 > lng2) {
        if (parseFloat(lng1 - lng2) > 180) {
            if (lng2 < 0) {
                lng2 = parseFloat(180 + 180 + lng2)
            }
        }
    }
    j = 0;
    t2 = 0;
    if (lat2 == lat1) {
        t = 0;
        h = lng1 - lng2
    } else {
        if (lng2 == lng1) {
            t = Math.PI / 2;
            h = lat1 - lat2
        } else {
            t = Math.atan((lat2 - lat1) / (lng2 - lng1));
            h = (lat2 - lat1) / Math.sin(t)
        }
    }
    if (t2 == 0) {
        t2 = (t + (Math.PI / 5))
    }
    h2 = h / 2;
    lng3 = h2 * Math.cos(t2) + lng1;
    lat3 = h2 * Math.sin(t2) + lat1;
    for (i = 0; i < count + 1; i++) {
        curveCoordinates.push(
            {
                lng: (lng1 * B1(inc) + lng3 * B2(inc)) + lng2 * B3(inc),
                lat: (lat1 * B1(inc) + lat3 * B2(inc) + lat2 * B3(inc))
            }
        );
        inc = inc + (1 / count)
    }
    return curveCoordinates
}

function getCurvePoints(points) {
    var curvePoints = [];
    for (var i = 0; i < points.length - 1; i++) {
        var p = getCurveByTwoPoints(points[i], points[i + 1]);
        if (p && p.length > 0) {
            curvePoints = curvePoints.concat(p)
        }
    }
    return curvePoints
}

let trackPoints = [{lng:113.281, lat:29.203}, {lng:113.567, lat:29.301}]

let convertPoints = getCurvePoints(trackPoints)

console.log(convertPoints)

最後再給一個微信小程序應用實例

map.wxml

// 舉個小程序應用的例子
<map id="map" longitude="113.324520" latitude="23.099994" scale="14" controls="{{controls}}" bindcontroltap="controltap" markers="{{markers}}" bindmarkertap="markertap" polyline="{{polyline}}" bindregionchange="regionchange" show-location style="width:100vw;height:100vh;"></map>

map.js

Page({
  data: {
    markers: [{
      iconPath: "/resources/marker.png",
      id: 0,
      latitude: 23.099994,
      longitude: 113.324520,
      width: 50,
      height: 50
    }],
    polyline: [],
    controls: [{
      id: 1,
      iconPath: '/resources/location.png',
      position: {
        left: 0,
        top: 300 - 50,
        width: 50,
        height: 50
      },
      clickable: true
    }]
  },
  onLoad() {
    this.setData({
      polyline:[{
        points: this.getCurvePoints([{ lng: 113.3245211, lat: 23.10229 }, { lng: 113.324520, lat: 23.21229 }]),
        color: "#FF0000DD",
        width: 2
      }]
    })
  },
  regionchange(e) {
    console.log(e.type)
  },
  markertap(e) {
    console.log(e.markerId)
  },
  controltap(e) {
    console.log(e.controlId)
  },
  getCurveByTwoPoints(obj1, obj2) {
    if (!obj1 || !obj2) {
      return null
    }
    var B1 = function (x) {
      return 1 - 2 * x + x * x
    };
    var B2 = function (x) {
      return 2 * x - 2 * x * x
    };
    var B3 = function (x) {
      return x * x
    };
    var curveCoordinates = [];
    var count = 30;
    var isFuture = false;
    var t, h, h2, lat3, lng3, j, t2;
    var LnArray = [];
    var i = 0;
    var inc = 0;
    if (typeof (obj2) == "undefined") {
      if (typeof (curveCoordinates) != "undefined") {
        curveCoordinates = []
      }
      return
    }
    var lat1 = parseFloat(obj1.lat);
    var lat2 = parseFloat(obj2.lat);
    var lng1 = parseFloat(obj1.lng);
    var lng2 = parseFloat(obj2.lng);
    if (lng2 > lng1) {
      if (parseFloat(lng2 - lng1) > 180) {
        if (lng1 < 0) {
          lng1 = parseFloat(180 + 180 + lng1)
        }
      }
    }
    if (lng1 > lng2) {
      if (parseFloat(lng1 - lng2) > 180) {
        if (lng2 < 0) {
          lng2 = parseFloat(180 + 180 + lng2)
        }
      }
    }
    j = 0;
    t2 = 0;
    if (lat2 == lat1) {
      t = 0;
      h = lng1 - lng2
    } else {
      if (lng2 == lng1) {
        t = Math.PI / 2;
        h = lat1 - lat2
      } else {
        t = Math.atan((lat2 - lat1) / (lng2 - lng1));
        h = (lat2 - lat1) / Math.sin(t)
      }
    }
    if (t2 == 0) {
      t2 = (t + (Math.PI / 5))
    }
    h2 = h / 2;
    lng3 = h2 * Math.cos(t2) + lng1;
    lat3 = h2 * Math.sin(t2) + lat1;
    for (i = 0; i < count + 1; i++) {
      curveCoordinates.push(
        {
          longitude: (lng1 * B1(inc) + lng3 * B2(inc)) + lng2 * B3(inc),
          latitude: (lat1 * B1(inc) + lat3 * B2(inc) + lat2 * B3(inc))
        }
      );
      inc = inc + (1 / count)
    }
    return curveCoordinates
  },
  getCurvePoints(points) {
    var curvePoints = [];
    for (var i = 0; i < points.length - 1; i++) {
      var p = this.getCurveByTwoPoints(points[i], points[i + 1]);
      if (p && p.length > 0) {
        curvePoints = curvePoints.concat(p)
      }
    }
    return curvePoints
  }
})

獻上效果圖：

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