原文链接及内容

原文链接：https://openlayers.org/en/latest/examples/tissot.html

运行界面

在地图上绘制Tissot指示性椭圆。上方地图的投影为EPSG:4326，下方地图的投影为EPSG:3857。

main.js代码如下：

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
import Feature from 'ol/Feature.js';
import Map from 'ol/Map.js';
import TileWMS from 'ol/source/TileWMS.js';
import VectorSource from 'ol/source/Vector.js';
import View from 'ol/View.js';
import {Tile as TileLayer, Vector as VectorLayer} from 'ol/layer.js';
import {circular as circularPolygon} from 'ol/geom/Polygon.js';

const vectorLayer4326 = new VectorLayer({
  source: new VectorSource(),
});

const vectorLayer3857 = new VectorLayer({
  source: new VectorSource(),
});

const map4326 = new Map({
  layers: [
    new TileLayer({
      source: new TileWMS({
        url: 'https://ahocevar.com/geoserver/wms',
        params: {
          'LAYERS': 'ne:NE1_HR_LC_SR_W_DR',
          'TILED': true,
        },
      }),
    }),
    vectorLayer4326,
  ],
  target: 'map4326',
  view: new View({
    projection: 'EPSG:4326',
    center: [0, 0],
    zoom: 2,
  }),
});

const map3857 = new Map({
  layers: [
    new TileLayer({
      source: new TileWMS({
        url: 'https://ahocevar.com/geoserver/wms',
        params: {
          'LAYERS': 'ne:NE1_HR_LC_SR_W_DR',
          'TILED': true,
        },
      }),
    }),
    vectorLayer3857,
  ],
  target: 'map3857',
  view: new View({
    center: [0, 0],
    zoom: 2,
  }),
});

const radius = 800000;
let x, y;
for (x = -180; x < 180; x += 30) {
  for (y = -90; y <= 90; y += 30) {
    const circle4326 = circularPolygon([x, y], radius, 64);
    const circle3857 = circle4326.clone().transform('EPSG:4326', 'EPSG:3857');
    vectorLayer4326.getSource().addFeature(new Feature(circle4326));
    vectorLayer3857.getSource().addFeature(new Feature(circle3857));
  }
}

界面布局文件index.html代码如下：

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8">
    <title>Tissot Indicatrix</title>
    <link rel="stylesheet" href="node_modules/ol/ol.css">
    <style>
      .map {
        width: 100%;
        height: 400px;
      }
    </style>
  </head>
  <body>
    <h4>EPSG:4326</h4>
    <div id="map4326" class="map"></div>
    <h4>EPSG:3857</h4>
    <div id="map3857" class="map"></div>
    <!-- Pointer events polyfill for old browsers, see https://caniuse.com/#feat=pointer -->
    <script src="https://cdn.jsdelivr.net/npm/elm-pep@1.0.6/dist/elm-pep.js"></script>
    <script type="module" src="main.js"></script>
  </body>
</html>