原文链接及内容

原文链接：https://openlayers.org/en/latest/examples/cog-style.html

运行界面

如果要根据应用程序状态的某些变化来更改WebGL切片图层的样式，则应使用layer.updateStyleVariables()方法。即使在每个渲染帧上更改了样式变量，也可以高效地渲染图层。在需要完全替换图层样式的情况下，可以调用layer.setStyle()方法。不应在响应频繁的用户事件(例如，鼠标移动、拖动滑块等)时调用此方法。

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
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
import GeoTIFF from 'ol/source/GeoTIFF.js';
import Map from 'ol/Map.js';
import TileLayer from 'ol/layer/WebGLTile.js';
import View from 'ol/View.js';

const max = 3000;
function normalize(value) {
  return ['/', value, max];
}

const red = normalize(['band', 1]);
const green = normalize(['band', 2]);
const blue = normalize(['band', 3]);
const nir = normalize(['band', 4]);

const trueColor = {
  color: ['array', red, green, blue, 1],
  gamma: 1.1,
};

const falseColor = {
  color: ['array', nir, red, green, 1],
  gamma: 1.1,
};

const ndvi = {
  color: [
    'interpolate',
    ['linear'],
    ['/', ['-', nir, red], ['+', nir, red]],
    // color ramp for NDVI values, ranging from -1 to 1
    // color ramp：色带，颜色渐变
    -0.2,
    [191, 191, 191],
    -0.1,
    [219, 219, 219],
    0,
    [255, 255, 224],
    0.025,
    [255, 250, 204],
    0.05,
    [237, 232, 181],
    0.075,
    [222, 217, 156],
    0.1,
    [204, 199, 130],
    0.125,
    [189, 184, 107],
    0.15,
    [176, 194, 97],
    0.175,
    [163, 204, 89],
    0.2,
    [145, 191, 82],
    0.25,
    [128, 179, 71],
    0.3,
    [112, 163, 64],
    0.35,
    [97, 150, 54],
    0.4,
    [79, 138, 46],
    0.45,
    [64, 125, 36],
    0.5,
    [48, 110, 28],
    0.55,
    [33, 97, 18],
    0.6,
    [15, 84, 10],
    0.65,
    [0, 69, 0],
  ],
};

const layer = new TileLayer({
  style: trueColor,
  source: new GeoTIFF({
    normalize: false,
    sources: [
      {
        url: 'https://s2downloads.eox.at/demo/EOxCloudless/2020/rgbnir/s2cloudless2020-16bits_sinlge-file_z0-4.tif',
      },
    ],
  }),
});

const map = new Map({
  target: 'map',
  layers: [layer],
  view: new View({
    projection: 'EPSG:4326',
    center: [0, 0],
    zoom: 2,
    maxZoom: 6,
  }),
});

const styles = {trueColor, falseColor, ndvi};
const styleSelector = document.getElementById('style');

function update() {
  const style = styles[styleSelector.value];
  layer.setStyle(style);
}
styleSelector.addEventListener('change', update);

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
24
25
26
<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8">
    <title>Change Tile Layer Style</title>
    <link rel="stylesheet" href="node_modules/ol/ol.css">
    <style>
      .map {
        width: 100%;
        height: 400px;
      }
    </style>
  </head>
  <body>
    <div id="map" class="map"></div>
    Set the layer style
    <select id="style">
      <option value="trueColor">True Color</option>
      <option value="falseColor">False Color</option>
      <option value="ndvi">NDVI</option>
    </select>
    <!-- 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>