添加相关计算的方法和逻辑

ellipsode.js

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+//椭球相关参数计算
+const a = 6378137; //长半轴 a
+const f = 1 / 298.257223563; //扁率 (a-b)/a
+const b = a * (1 - f);//短半轴 b
+const e = Math.sqrt(a * a - b * b) / a;//椭球第一偏心率
+
+// console.log(a);
+// console.log(f);
+// console.log(b);
+// console.log(e);
+// console.log(e*e);
+
+function degToRad(deg) {
+    return deg / 180 * Math.PI;
+}
+
+function radToDeg(rad) {
+    return rad / Math.PI * 180;
+}
+
+function wgs84ToWebMercator(lat, lon) {
+    let x = a * lon;
+    let y = a * Math.log(Math.tan(Math.PI / 4 + lat / 2));
+    return { x: x, y: y };
+}
+
+function webMercatorToWgs84(x, y) {
+    let lon = x / a;
+    let lat = 2 * Math.atan(Math.pow(Math.E, y / a)) - Math.PI / 2;
+    return { lon: lon, lat: lat }
+}
+
+// console.log(wgs84ToWebMercator(degToRad(50), degToRad(50)));
+// console.log(wgs84ToWebMercator(degToRad(49.99999999999999), degToRad(49.99999999999999)));
+// let wgs = webMercatorToWgs84(5565974.539663678, 6446275.841017158);
+// console.log(wgs);
+// console.log('lat: ' + radToDeg(wgs.lat) + ','
+//     + 'lon:' + radToDeg(wgs.lon));
+
+
+// console.log(2 * Math.atan(Math.pow(Math.E, 0 / a)) - Math.PI / 2);
+// console.log(radToDeg(webMercatorToWgs84(5565974.539663678, 0).lat));
+
+function lon2tile(lon, z) {
+    return (Math.floor((lon + 180) / 360 * Math.pow(2, z)));
+}
+
+function lat2tile(lat, z) {
+    return (Math.floor((1 - Math.log(Math.tan(lat * Math.PI / 180)
+        + 1 / Math.cos(lat * Math.PI / 180)) / Math.PI)
+        / 2 * Math.pow(2, z)));
+}
+
+function lon2x(lon, z) {
+    return ((lon + 180) / 360 * Math.pow(2, z));
+}
+
+function lat2y(lat, z) {
+    return ((1 - Math.log(Math.tan(lat * Math.PI / 180)
+        + 1 / Math.cos(lat * Math.PI / 180)) / Math.PI)
+        / 2 * Math.pow(2, z));
+}
+
+function tile2long(x, z) {
+    return (x / Math.pow(2, z) * 360 - 180);
+}
+function tile2lat(y, z) {
+    var n = Math.PI - 2 * Math.PI * y / Math.pow(2, z);
+    return (180 / Math.PI * Math.atan(0.5 * (Math.exp(n) - Math.exp(-n))));
+}
+
+//test
+//22.7490073, 114.3781213  z=15
+//let mappiece = Math.pow(2, zoom_level); //一个方向的地图块数 1块256个像素
+
+// console.log(lon2tile(long, zoom_level));
+// console.log(lat2tile(lat, zoom_level));
+// console.log(lon2x(long, zoom_level));
+// console.log(lat2y(lat, zoom_level));
+
+// console.log('----------------------');
+// console.log(tile2long(26794, zoom_level));
+// console.log(tile2long(26794 + 1 / 256, zoom_level));
+
+//https://tile.openstreetmap.org/z/x/y.png
+//https://tile.openstreetmap.org/15/26794/14256.png
+
+let zoom_level = 15;
+let lat = 22.7490073;
+let long = 114.3781213;
+let x = lon2x(long, zoom_level);
+let y = lat2y(lat, zoom_level);
+
+let tilex = lon2tile(long, zoom_level);
+let tiley = lat2tile(lat, zoom_level);
+
+let offsetx = Math.floor((x - tilex) * 256);
+let offsety = Math.floor((y - tiley) * 256);
+
+//计算出瓦片地图的基准坐标,假设显示的宽高为1600*900
+let width = 1600;
+let height = 900;
+let minx = width / 2 - offsetx;
+let maxx = minx + 256;
+let miny = height / 2 - offsety;
+let maxy = miny + 256;
+
+//计算出四个方向各需要的块数
+//p1 p2 p3 p4 上 下 左 右
+let p1 = Math.floor(maxy / 256 + 0.5);
+let p2 = Math.floor((height - miny) / 256 + 0.5);
+let p3 = Math.floor(maxx / 256 + 0.5);
+let p4 = Math.floor((width - minx) / 256 + 0.5);
+
+//基于已知条件计算需要的各个tile
+let tiles = new Array();
+tiles.push({ x: tilex, y: tiley });
+for (let i = 1; i < p4; i++) {
+    tiles.push({ x: tilex + i, y: tiley });
+}
+for (let i = 1; i < p3; i++) {
+    tiles.push({ x: tilex - i, y: tiley });
+}
+for (let i = 1; i < p1; i++) {
+    for (let j = 0; j < p3 + p4 - 1; j++) {
+        tiles.push({ x: tilex - p3 + 1 + j, y: tiley - i });
+    }
+}
+for (let i = 1; i < p2; i++) {
+    for (let j = 0; j < p3 + p4 - 1; j++) {
+        tiles.push({ x: tilex - p3 + 1 + j, y: tiley + i });
+    }
+}
+console.log(tiles);
+console.log(tiles.length);
+
+//渲染问题
+//通过与基准之间的位置关系计算渲染的坐标
+//minx miny 即为基准tile当前渲染位置
+
+for (let i = 0; i < tiles.length; i++) {
+    const element = tiles[i];
+    let renderx = (element.x - tilex) * 256 + minx;
+    let rendery = (element.y - tiley) * 256 + miny;
+    console.log({ x: renderx, y: rendery });
+}

index.html

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+<!DOCTYPE html>
+<html lang="en">
+    <head>
+        <meta charset="UTF-8">
+        <meta http-equiv="X-UA-Compatible" content="IE=edge">
+        <meta name="viewport" content="width=device-width, initial-scale=1.0">
+        <title>tilerendertest</title>
+        <style>
+            *{
+                margin: 0;
+                padding: 0;
+            }
+            .main{
+                display: flex;
+                justify-content: center;
+                align-items: center;
+                background-color: white;
+                width: 100vw;
+                height: 100vh;
+            }
+            .container{
+                flex:1;
+                display: flex;
+                justify-content: center;
+                align-items: center;
+            }
+            .map{
+                background-color: rgb(79, 38, 38);
+                width: 1600px;
+                height: 900px;
+            }
+        </style>
+    </head>
+    <body>
+        <div class="main">
+            <div class="container">
+                <canvas class="map" id="map"></canvas>
+            </div>
+        </div>
+        <script src="./ellipsode.js"></script>
+    </body>
+</html>