Openlayers4中风场的实现
概述：
本文讲述如何在Openlayers4中结合canvas实现风场的展示。
效果：
代码：
1、数据结构
[lat, lon, wd, ws]，其中：lat为纬度；lon为经度；wd为风向；ws为风速。
2、wind扩展
/**
* @author lzugis
* @Date
* 1.计算矩形4个角的canvas坐标x、y，初始化该区域所有网格点，间距可根据map index设置
* 2.将已有的站点经纬度转换为canvas坐标
* 3.插值法计算出每个网格点的风向、风速
* 4.在该网格区域随机生成width*8个点，重复运动
*/
var Windy = function (options) {
var MAX_PARTICLE_AGE = 100; //粒子最大运动次数
var FRAME_RATE = 20; //重绘帧数
var PARTICLE_MULTIPLIER = 8;
var canvas = options.canvas;
var width = canvas.width;
var height = canvas.height;
var ctx = canvas.getContext('2d');
ctx.lineWidth = .8;
ctx.fillStyle = 'rgba(0,0,0,.97)';
// ctx.strokeStyle = 'rgba(38,173,133,0.8)';
var buildBounds = function (extent, callback) {
var upperLeft = extent[0];
var lowerRight = extent[1];
var bounds = {
x: upperLeft[0],
y: upperLeft[1],
xmax: lowerRight[0],
ymax: lowerRight[1],
width: lowerRight[0] - upperLeft[0],
height: lowerRight[1] - upperLeft[1]
};
callback(bounds);
}
var createField = function (columns, bounds, callback) {
function vector(x, y) {
var column = columns[Math.floor(x)];
return column && column[Math.floor(y)];
}
vector.release = function () {
columns = [];
}
vector.randomize = function (o) {
var x = Math.floor(Math.floor(Math.random() * bounds.width) + bounds.x);
var y = Math.floor(Math.floor(Math.random() * bounds.height) + bounds.y);
o.x = x;
o.y = y;
return o;
}
callback(bounds, vector);
};
var interpolateGrid = function (bounds, stationPoints, callback) {
var columns = [];
var x = bounds.x;
function interpolateColumn(x) {
var column = [];
for (var y = bounds.y; y < bounds.ymax; y += 2) {
var wind = interpolate(x, y);
column[y + 1] = column[y] = wind;
}
columns[x + 1] = columns[x] = column;
}
function interpolate(x, y) {
var angle0 = 0,
angle1 = 0,
speed0 = 0,
speed1 = 0,
wind = {};
stationPoints.forEach(function (s) {
angle0 += s.angle * 1.0 / ((y - s.y) * (y - s.y) + (x - s.x) * (x - s.x));
angle1 += 1.0 / ((y - s.y) * (y - s.y) + (x - s.x) * (x - s.x));
speed0 += s.speed * 1.0 / ((y - s.y) * (y - s.y) + (x - s.x) * (x - s.x));
speed1 += 1.0 / ((y - s.y) * (y - s.y) + (x - s.x) * (x - s.x));
if (angle1 != 0) {
wind.angle = angle0 / angle1;
}
if (speed1 != 0) {
wind.speed = speed0 / speed1;
}
});
return wind;
}
(function batchInterpolate() {
var start = Date.now();
while (x < bounds.xmax) {
interpolateColumn(x);
x += 2;
if ((Date.now() - start) > 1000) { //MAX_TASK_TIME
setTimeout(batchInterpolate, 25);
return;
}
}
createField(columns, bounds, callback);
})();
};
var animate = function (bounds, vector) {
var particleCount = Math.round(bounds.width * PARTICLE_MULTIPLIER);
var particles = [];
for (var i = 0; i < particleCount; i++) {
particles.push(vector.randomize({
age: Math.floor(Math.random() * MAX_PARTICLE_AGE)
}));
}
function evolve() {
particles.forEach(function (particle, i) {
if (particle.age > MAX_PARTICLE_AGE) {
particle = vector.randomize({
age: 0
});
particles.splice(i, 1, particle);
}
var x = particle.x;
var y = particle.y;
var v = vector(x, y);
if (v) {
var xe = x - v.speed * Math.sin(Math.PI / 180 * (180 - v.angle));
var ye = y - v.speed * Math.cos(Math.PI / 180 * (180 - v.angle));
var nextPoint = vector(xe, ye);
if (nextPoint) {
particle.xe = xe;
particle.ye = ye;
} else {
var newParticle = vector.randomize({
age: Math.floor(Math.random() * MAX_PARTICLE_AGE)
});
particles.splice(i, 1, newParticle);
}
} else {
particle.age = MAX_PARTICLE_AGE;
}
particle.age += 1;
});
}
function render() {
var prev = ctx.globalCompositeOperation;
ctx.globalCompositeOperation = "destination-in";
ctx.fillRect(0, 0, width, height);
ctx.globalCompositeOperation = prev;
ctx.beginPath();
// ctx.strokeStyle = 'rgba(23,139,231,.8)';
particles.forEach(function (particle, i) {
ctx.moveTo(particle.x, particle.y);
ctx.lineTo(particle.xe, particle.ye);
particle.x = particle.xe;
particle.y = particle.ye;
});
ctx.stroke();
}
(function frame() {
try {
windy.timer = setTimeout(function () {
requestAnimationFrame(frame);
evolve();
render();
}, 1000 / FRAME_RATE);
} catch (e) {
console.error(e);
}
})();
};
var start = function (extent, stationPoints) {
stop();
buildBounds(extent, function (bounds) {
interpolateGrid(bounds, stationPoints, function (bounds, vector) {
windy.vector = vector;
animate(bounds, vector);
});
});
};
var stop = function () {
ctx.clearRect(0, 0, width, height);
if (windy.vector) windy.vector.release();
if (windy.timer) clearTimeout(windy.timer);
};
var change = function (options) {
ctx.lineWidth = options.size;
ctx.strokeStyle = options.color;
}
var windy = {
options: options,
start: start,
stop: stop,
change: change
};
return windy;
};
window.requestAnimationFrame = (function () {
return window.requestAnimationFrame ||
window.webkitRequestAnimationFrame ||
window.mozRequestAnimationFrame ||
window.oRequestAnimationFrame ||
window.msRequestAnimationFrame ||
function (callback) {
window.setTimeout(callback, 1000 / 20);
};
})();3、调用实现
var canvas, windy;
function addWindMap(){
canvas = document.createElement('canvas');
canvas.id = "windCanvas";
canvas.width = map.getSize()[0];
canvas.height = map.getSize()[1];
canvas.style.position = 'absolute';
canvas.style.top = 0;
canvas.style.left = 0;
map.getViewport().appendChild(canvas);
windy = new Windy({
map: map,
canvas: canvas,
data: windData
});
var options = {
size: .8,
color: 'rgba(71,160,233,0.8)',
};
windy.change(options);
windDraw();
map.getView().on('propertychange',function(){
windy.stop();
$(canvas).hide();
});
map.on("moveend",function(){
windDraw();
});
}
function windDraw(){
$(canvas).show();
var bounds = map.getView().calculateExtent();
var _min = [bounds[0], bounds[1]];
var _max = [bounds[2], bounds[3]];
var py = map.getPixelFromCoordinate([bounds[0], bounds[3]]); //经纬度转成屏幕坐标
canvas.style.left = py.x + 'px';
canvas.style.top = py.y + 'px';
var points = invertLatLon(py); //所有站点经纬度转为canvas坐标
var min = map.getPixelFromCoordinate(_min);
var max = map.getPixelFromCoordinate(_max);
var extent = [
[min[0] - py[0], max[1] - py[1]],
[max[0] - py[0], min[1] - py[1]]
];
windy.start(extent, points);
}
function invertLatLon (py) {
var points = [];
windData.forEach(function (station) {
var px = map.getPixelFromCoordinate([station[1], station[0]]);
points.push({
x: px[0]-py[0],
y: px[1]-py[1],
angle: station[2],
speed: station[3]
});
});
return points;
}———————————————————————————————-
技术博客
CSDN：http://blog.csdn.NET/gisshixisheng
博客园：http://www.cnblogs.com/lzugis/
在线教程
http://edu.csdn.Net/course/detail/799
Github
https://github.com/lzugis/
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转载自：https://blog.csdn.net/GISShiXiSheng/article/details/78130113
