mapboxGL之风流图

概述

前面的文章说到了Openlayers4中风场的实现,本文将讲述如何在mapbox GL实现类似的效果。

效果

[外链图片转存失败,源站可能有防盗链机制,建议将图片保存下来直接上传(img-ZkUGd75p-1585748579661)(https://upload-images.jianshu.io/upload_images/6826673-a72b98f01e6917fa.gif?imageMogr2/auto-orient/strip)]

实现

实现是在windy-esri的基础上做了和mapboxGL的结合,结合代码如下:

var windyMap = {
  windy: null,
  map: null,
  visible: true,

  initWindy(data, map) {
    const self = this;
    self.visible = true;
    self.map = map;

    // 删除dom
    self.hideWind();

    let canvas = document.createElement('canvas');
    canvas.id = 'windCanvas';
    canvas.width = map.getCanvas().width;
    canvas.height = map.getCanvas().height;
    canvas.style.position = 'absolute';
    canvas.style.top = 0;
    canvas.style.left = 0;
    map.getCanvasContainer().appendChild(canvas);

    self.windy = new Windy({
      canvas: canvas,
      data: data
    });
    self._refreshWindy();
    map.on('render', function() {
      if (self.visible) self._refreshWindy();
    });

  },
  _refreshWindy: function() {
    const self = this;
    const _canvas = self.windy.params.canvas;
    _canvas.style.display = 'block';
    if (!self.windy) return;
    self.windy.stop();
    let bounds = self.map.getBounds();
    let extent = [
      bounds._sw.lng,
      bounds._sw.lat,
      bounds._ne.lng,
      bounds._ne.lat
    ];

    _canvas.width = map.getCanvas().width;
    _canvas.height = map.getCanvas().height;

    self.windy.start(
      [[0, 0], [_canvas.width, _canvas.height]],
      _canvas.width,
      _canvas.height,
      [[extent[0], extent[1]], [extent[2], extent[3]]]
    );
  },

  hideWind: function() {
    let dom = document.getElementById('windCanvas');
    if (dom) dom.parentNode.removeChild(dom);
  },

  setVisible: function(flag) {
    const self = this;
    self.visible = flag;
    let dom = document.getElementById('windCanvas');
    if (!dom) return;
    if (flag) {
      dom.style.display = 'block';
      self._refreshWindy();
    } else {
      if (self.windy) self.windy.stop();
      dom.style.display = 'none';
    }
  }
};

说明:这里面核心用到了mapboxGL的接口有:map.getCanvasContainer()map.getBounds()map.getCanvas()

windy.js的代码如下:

var Windy = function( params ){
  var velocity = params.velocity? params.velocity: 0.012,
    step = params.step? params.step: 1000,
    particle = params.particle? params.particle: 500,
    width = params.width? params.width: 3,
    intensity = params.intensity? params.intensity: 15;

  // scale for wind velocity速度
  var VELOCITY_SCALE =velocity * (Math.pow(window.devicePixelRatio,1/3) || 1);

  // step size of particle intensity color scale颗粒强度色标的步长
  var INTENSITY_SCALE_STEP =step;

  // wind velocity at which particle intensity is maximum (m/s)粒子强度最大的风速 (米/秒)
  var MAX_WIND_INTENSITY = intensity;

  // max number of frames a particle is drawn before regeneration在再生前绘制粒子的最大帧数
  var MAX_PARTICLE_AGE = 50;

  // line width of a drawn particle绘制粒子的线宽
  var PARTICLE_LINE_WIDTH = width;

  // particle count scalar (completely arbitrary--this values looks nice)粒子计数标量
  var PARTICLE_MULTIPLIER = 1/particle;

  // reduce particle count to this much of normal for mobile devices减少对移动设备的这一大部分正常的粒子计数
  var PARTICLE_REDUCTION = 0.5;

  // desired milliseconds per frame每帧所需的毫秒数
  var FRAME_RATE = 10;

  // singleton for no wind in the form: [u, v, magnitude]
  var NULL_WIND_VECTOR = [NaN, NaN, null];

  // interpolation for vectors like wind (u,v,m)
  var bilinearInterpolateVector = function(x, y, g00, g10, g01, g11) {
    var rx = (1 - x);
    var ry = (1 - y);
    var a = rx * ry,  b = x * ry,  c = rx * y,  d = x * y;
    var u = g00[0] * a + g10[0] * b + g01[0] * c + g11[0] * d;
    var v = g00[1] * a + g10[1] * b + g01[1] * c + g11[1] * d;
    return [u, v, Math.sqrt(u * u + v * v)];
  };


  var createWindBuilder = function(uComp, vComp) {
    var uData = uComp.data, vData = vComp.data;
    return {
      header: uComp.header,
      //recipe: recipeFor("wind-" + uComp.header.surface1Value),
      data: function(i) {
        var _uDatai = uData[i],
          _vDatai = vData[i];
        _uDatai = Math.abs(_uDatai)>360?0:_uDatai;
        _vDatai = Math.abs(_vDatai)>360?0:_vDatai;
        return [_uDatai, _vDatai];
      },
      interpolate: bilinearInterpolateVector
    }
  };

  var createBuilder = function(data) {
    var uComp = null, vComp = null, scalar = null;

    data.forEach(function(record) {
      switch (record.header.parameterCategory + "," + record.header.parameterNumber) {
        case "2,2": uComp = record; break;
        case "2,3": vComp = record; break;
        default:
          scalar = record;
      }
    });

    return createWindBuilder(uComp, vComp);
  };

  var buildGrid = function(data, callback) {
    var builder = createBuilder(data);

    var header = builder.header;
    var λ0 = header.lo1, φ0 = header.la1;  // the grid's origin (e.g., 0.0E, 90.0N)
    var Δλ = header.dx, Δφ = header.dy;    // distance between grid points (e.g., 2.5 deg lon, 2.5 deg lat)
    var ni = header.nx, nj = header.ny;    // number of grid points W-E and N-S (e.g., 144 x 73)
    var date = new Date(header.refTime);
    date.setHours(date.getHours() + header.forecastTime);

    // Scan mode 0 assumed. Longitude increases from λ0, and latitude decreases from φ0.
    // http://www.nco.ncep.noaa.gov/pmb/docs/grib2/grib2_table3-4.shtml
    var grid = [], p = 0;
    var isContinuous = Math.floor(ni * Δλ) >= 360;
    for (var j = 0; j < nj; j++) {
      var row = [];
      for (var i = 0; i < ni; i++, p++) {
        row[i] = builder.data(p);
      }
      if (isContinuous) {
        // For wrapped grids, duplicate first column as last column to simplify interpolation logic
        row.push(row[0]);
      }
      grid[j] = row;
    }

    function interpolate(λ, φ) {
      var i = floorMod(λ - λ0, 360) / Δλ;  // calculate longitude index in wrapped range [0, 360)
      var j = (φ0 - φ) / Δφ;                 // calculate latitude index in direction +90 to -90

      var fi = Math.floor(i), ci = fi + 1;
      var fj = Math.floor(j), cj = fj + 1;

      var row;
      if ((row = grid[fj])) {
        var g00 = row[fi];
        var g10 = row[ci];
        if (isValue(g00) && isValue(g10) && (row = grid[cj])) {
          var g01 = row[fi];
          var g11 = row[ci];
          if (isValue(g01) && isValue(g11)) {
            // All four points found, so interpolate the value.
            return builder.interpolate(i - fi, j - fj, g00, g10, g01, g11);
          }
        }
      }
      return null;
    }
    callback( {
      date: date,
      interpolate: interpolate
    });
  };



  /**
   * @returns {Boolean} true if the specified value is not null and not undefined.
   */
  var isValue = function(x) {
    return x !== null && x !== undefined;
  }

  /**
   * @returns {Number} returns remainder of floored division, i.e., floor(a / n). Useful for consistent modulo
   *          of negative numbers. See http://en.wikipedia.org/wiki/Modulo_operation.
   */
  var floorMod = function(a, n) {
    return a - n * Math.floor(a / n);
  }

  /**
   * @returns {Number} the value x clamped to the range [low, high].
   */
  var clamp = function(x, range) {
    return Math.max(range[0], Math.min(x, range[1]));
  }

  /**
   * @returns {Boolean} true if agent is probably a mobile device. Don't really care if this is accurate.
   */
  var isMobile = function() {
    return (/android|blackberry|iemobile|ipad|iphone|ipod|opera mini|webos/i).test(navigator.userAgent);
  }

  /**
   * Calculate distortion of the wind vector caused by the shape of the projection at point (x, y). The wind
   * vector is modified in place and returned by this function.
   */
  var distort = function(projection, λ, φ, x, y, scale, wind, windy) {
    var u = wind[0] * scale;
    var v = wind[1] * scale;
    var d = distortion(projection, λ, φ, x, y, windy);

    // Scale distortion vectors by u and v, then add.
    wind[0] = d[0] * u + d[2] * v;
    wind[1] = d[1] * u + d[3] * v;
    return wind;
  };

  var distortion = function(projection, λ, φ, x, y, windy) {
    var τ = 2 * Math.PI;
    var H = Math.pow(10, -5.2);
    var hλ = λ < 0 ? H : -H;
    var hφ = φ < 0 ? H : -H;

    var pλ = project(φ, λ + hλ,windy);
    var pφ = project(φ + hφ, λ, windy);

    // Meridian scale factor (see Snyder, equation 4-3), where R = 1. This handles issue where length of 1º λ
    // changes depending on φ. Without this, there is a pinching effect at the poles.
    var k = Math.cos(φ / 360 * τ);
    return [
      (pλ[0] - x) / hλ / k,
      (pλ[1] - y) / hλ / k,
      (pφ[0] - x) / hφ,
      (pφ[1] - y) / hφ
    ];
  };



  var createField = function(columns, bounds, callback) {

    /**
     * @returns {Array} wind vector [u, v, magnitude] at the point (x, y), or [NaN, NaN, null] if wind
     *          is undefined at that point.
     */
    function field(x, y) {
      var column = columns[Math.round(x)];
      return column && column[Math.round(y)] || NULL_WIND_VECTOR;
    }

    // Frees the massive "columns" array for GC. Without this, the array is leaked (in Chrome) each time a new
    // field is interpolated because the field closure's context is leaked, for reasons that defy explanation.
    field.release = function() {
      columns = [];
    };

    field.randomize = function(o) {  // UNDONE: this method is terrible
      var x, y;
      var safetyNet = 0;
      do {
        x = Math.round(Math.floor(Math.random() * bounds.width) + bounds.x);
        y = Math.round(Math.floor(Math.random() * bounds.height) + bounds.y)
      } while (field(x, y)[2] === null && safetyNet++ < 30);
      o.x = x;
      o.y = y;
      return o;
    };

    //field.overlay = mask.imageData;
    //return field;
    callback( bounds, field );
  };

  var buildBounds = function( bounds, width, height ) {
    var upperLeft = bounds[0];
    var lowerRight = bounds[1];
    var x = Math.round(upperLeft[0]); //Math.max(Math.floor(upperLeft[0], 0), 0);
    var y = Math.max(Math.floor(upperLeft[1], 0), 0);
    var xMax = Math.min(Math.ceil(lowerRight[0], width), width - 1);
    var yMax = Math.min(Math.ceil(lowerRight[1], height), height - 1);
    return {x: x, y: y, xMax: width, yMax: yMax, width: width, height: height};
  };

  var deg2rad = function( deg ){
    return (deg / 180) * Math.PI;
  };

  var rad2deg = function( ang ){
    return ang / (Math.PI/180.0);
  };

  var invert = function(x, y, windy){
    var mapLonDelta = windy.east - windy.west;
    var worldMapRadius = windy.width / rad2deg(mapLonDelta) * 360/(2 * Math.PI);
    var mapOffsetY = ( worldMapRadius / 2 * Math.log( (1 + Math.sin(windy.south) ) / (1 - Math.sin(windy.south))  ));
    var equatorY = windy.height + mapOffsetY;
    var a = (equatorY-y)/worldMapRadius;

    var lat = 180/Math.PI * (2 * Math.atan(Math.exp(a)) - Math.PI/2);
    var lon = rad2deg(windy.west) + x / windy.width * rad2deg(mapLonDelta);
    return [lon, lat];
  };

  var mercY = function( lat ) {
    return Math.log( Math.tan( lat / 2 + Math.PI / 4 ) );
  };


  var project = function( lat, lon, windy) { // both in radians, use deg2rad if neccessary
    var ymin = mercY(windy.south);
    var ymax = mercY(windy.north);
    var xFactor = windy.width / ( windy.east - windy.west );
    var yFactor = windy.height / ( ymax - ymin );

    var y = mercY( deg2rad(lat) );
    var x = (deg2rad(lon) - windy.west) * xFactor;
    var y = (ymax - y) * yFactor; // y points south
    return [x, y];
  };


  var interpolateField = function( grid, bounds, extent, callback ) {
    var projection = {};
    var velocityScale = VELOCITY_SCALE;

    var columns = [];
    var x = bounds.x;

    function interpolateColumn(x) {
      var column = [];
      for (var y = bounds.y; y <= bounds.yMax; y += 2) {
        var coord = invert( x, y, extent );
        if (coord) {
          var λ = coord[0], φ = coord[1];
          if (isFinite(λ)) {
            var wind = grid.interpolate(λ, φ);
            if (wind) {
              wind = distort(projection, λ, φ, x, y, velocityScale, wind, extent);
              column[y+1] = column[y] = wind;

            }
          }
        }
      }
      columns[x+1] = columns[x] = column;
    }

    (function batchInterpolate() {
      var start = Date.now();
      while (x < bounds.width) {
        interpolateColumn(x);
        x += 2;
        if ((Date.now() - start) > 1000) { //MAX_TASK_TIME) {
          setTimeout(batchInterpolate, 25);
          return;
        }
      }
      createField(columns, bounds, callback);
    })();
  };


  var animate = function(bounds, field) {

    function asColorStyle(r, g, b, a) {
      return "rgba(" + 243 + ", " + 243 + ", " + 238 + ", " + a + ")";
    }

    function hexToR(h) {return parseInt((cutHex(h)).substring(0,2),16)}
    function hexToG(h) {return parseInt((cutHex(h)).substring(2,4),16)}
    function hexToB(h) {return parseInt((cutHex(h)).substring(4,6),16)}
    function cutHex(h) {return (h.charAt(0)=="#") ? h.substring(1,7):h}

    function windIntensityColorScale(step, maxWind) {

      var result = [
        /* blue to red*/
        "rgba(" + hexToR('#178be7') + ", " + hexToG('#178be7') + ", " + hexToB('#178be7') + ", " + 0.5 + ")",
        "rgba(" + hexToR('#8888bd') + ", " + hexToG('#8888bd') + ", " + hexToB('#8888bd') + ", " + 0.5 + ")",
        "rgba(" + hexToR('#b28499') + ", " + hexToG('#b28499') + ", " + hexToB('#b28499') + ", " + 0.5 + ")",
        "rgba(" + hexToR('#cc7e78') + ", " + hexToG('#cc7e78') + ", " + hexToB('#cc7e78') + ", " + 0.5 + ")",
        "rgba(" + hexToR('#de765b') + ", " + hexToG('#de765b') + ", " + hexToB('#de765b') + ", " + 0.5 + ")",
        "rgba(" + hexToR('#ec6c42') + ", " + hexToG('#ec6c42') + ", " + hexToB('#ec6c42') + ", " + 0.5 + ")",
        "rgba(" + hexToR('#f55f2c') + ", " + hexToG('#f55f2c') + ", " + hexToB('#f55f2c') + ", " + 0.5 + ")",
        "rgba(" + hexToR('#fb4f17') + ", " + hexToG('#fb4f17') + ", " + hexToB('#fb4f17') + ", " + 0.5 + ")",
        "rgba(" + hexToR('#fe3705') + ", " + hexToG('#fe3705') + ", " + hexToB('#fe3705') + ", " + 0.5 + ")",
        "rgba(" + hexToR('#ff0000') + ", " + hexToG('#ff0000') + ", " + hexToB('#ff0000') + ", " + 0.5 + ")"
        // "rgba(" + hexToR('#00ffff') + ", " + hexToG('#00ffff') + ", " + hexToB('#00ffff') + ", " + 0.5 + ")",
        // "rgba(" + hexToR('#64f0ff') + ", " + hexToG('#64f0ff') + ", " + hexToB('#64f0ff') + ", " + 0.5 + ")",
        // "rgba(" + hexToR('#87e1ff') + ", " + hexToG('#87e1ff') + ", " + hexToB('#87e1ff') + ", " + 0.5 + ")",
        // "rgba(" + hexToR('#a0d0ff') + ", " + hexToG('#a0d0ff') + ", " + hexToB('#a0d0ff') + ", " + 0.5 + ")",
        // "rgba(" + hexToR('#b5c0ff') + ", " + hexToG('#b5c0ff') + ", " + hexToB('#b5c0ff') + ", " + 0.5 + ")",
        // "rgba(" + hexToR('#c6adff') + ", " + hexToG('#c6adff') + ", " + hexToB('#c6adff') + ", " + 0.5 + ")",
        // "rgba(" + hexToR('#d49bff') + ", " + hexToG('#d49bff') + ", " + hexToB('#d49bff') + ", " + 0.5 + ")",
        // "rgba(" + hexToR('#e185ff') + ", " + hexToG('#e185ff') + ", " + hexToB('#e185ff') + ", " + 0.5 + ")",
        // "rgba(" + hexToR('#ec6dff') + ", " + hexToG('#ec6dff') + ", " + hexToB('#ec6dff') + ", " + 0.5 + ")",
        // "rgba(" + hexToR('#ff1edb') + ", " + hexToG('#ff1edb') + ", " + hexToB('#ff1edb') + ", " + 0.5 + ")"
      ];
      /*
      var result = [];
      for (var j = 225; j >= 100; j = j - step) {
        result.push(asColorStyle(j, j, j, 1));
      }
      */
      result.indexFor = function(m) {  // map wind speed to a style
        return Math.floor(Math.min(m, maxWind) / maxWind * (result.length - 1));
      };
      return result;
    }

    var colorStyles = windIntensityColorScale(INTENSITY_SCALE_STEP, MAX_WIND_INTENSITY);
    var buckets = colorStyles.map(function() { return []; });

    var particleCount = Math.round(bounds.width * bounds.height * PARTICLE_MULTIPLIER);
    if (isMobile()) {
      particleCount *= PARTICLE_REDUCTION;
    }

    var fadeFillStyle = "rgba(0, 0, 0, 0.97)";

    var particles = [];
    for (var i = 0; i < particleCount; i++) {
      particles.push(field.randomize({age: Math.floor(Math.random() * MAX_PARTICLE_AGE) + 0}));
    }

    function evolve() {
      buckets.forEach(function(bucket) { bucket.length = 0; });
      particles.forEach(function(particle) {
        if (particle.age > MAX_PARTICLE_AGE) {
          field.randomize(particle).age = 0;
        }
        var x = particle.x;
        var y = particle.y;
        var v = field(x, y);  // vector at current position
        var m = v[2];
        if (m === null) {
          particle.age = MAX_PARTICLE_AGE;  // particle has escaped the grid, never to return...
        }
        else {
          var xt = x + v[0];
          var yt = y + v[1];
          if (field(xt, yt)[2] !== null) {
            // Path from (x,y) to (xt,yt) is visible, so add this particle to the appropriate draw bucket.
            particle.xt = xt;
            particle.yt = yt;
            buckets[colorStyles.indexFor(m)].push(particle);
          }
          else {
            // Particle isn't visible, but it still moves through the field.
            particle.x = xt;
            particle.y = yt;
          }
        }
        particle.age += 1;
      });
    }

    var g = params.canvas.getContext("2d");
    g.lineWidth = PARTICLE_LINE_WIDTH;
    g.fillStyle = fadeFillStyle;

    function draw() {
      // Fade existing particle trails.
      var prev = g.globalCompositeOperation;
      g.globalCompositeOperation = "destination-in";
      g.fillRect(bounds.x, bounds.y, bounds.width, bounds.height);
      g.globalCompositeOperation = prev;

      // Draw new particle trails.
      buckets.forEach(function(bucket, i) {
        if (bucket.length > 0) {
          g.beginPath();
          g.strokeStyle = colorStyles[i];
          bucket.forEach(function(particle) {
            g.moveTo(particle.x, particle.y);
            g.lineTo(particle.xt, particle.yt);
            particle.x = particle.xt;
            particle.y = particle.yt;
          });
          g.stroke();
        }
      });
    }

    (function frame() {
      try {
        windy.timer = setTimeout(function() {
          requestAnimationFrame(frame);
          evolve();
          draw();
        }, 1000 / FRAME_RATE);
      }
      catch (e) {
        console.error(e);
      }
    })();
  };

  var start = function(bounds, width, height, extent ){
    var mapBounds = {
      south: deg2rad(extent[0][1]),
      north: deg2rad(extent[1][1]),
      east: deg2rad(extent[1][0]),
      west: deg2rad(extent[0][0]),
      width: width,
      height: height
    };

    stop();

    // build grid
    buildGrid( params.data, function(grid){
      // interpolateField
      interpolateField( grid, buildBounds( bounds, width, height), mapBounds, function( bounds, field ){
        // animate the canvas with random points
        windy.field = field;
        animate( bounds, field );
      });

    });
  };

  var stop = function(){
    if (windy.field) windy.field.release();
    if (windy.timer) clearTimeout(windy.timer)
  };

  var windy = {
    params: params,
    start: start,
    stop: stop
  };

  return windy;
};
// shim layer with setTimeout fallback
window.requestAnimationFrame = (function(){
  return  window.requestAnimationFrame       ||
    window.webkitRequestAnimationFrame ||
    window.mozRequestAnimationFrame    ||
    window.oRequestAnimationFrame ||
    window.msRequestAnimationFrame ||
    function( callback ){
      window.setTimeout(callback, 1000 / 20);
    };
})();

参考数据格式可从网盘下载:

链接:https://pan.baidu.com/s/1EiP90AH4YUR4nN79BT6xfw 
提取码:mes9 

调用时,可如下:

map.on('load', function() {
  $.get("../data/windy.json", function(res) {
    windyMap.initWindy(res, map);
  })
});

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