个人中心
退出
OpenLayers 5 使用GeoJSON进行行政区划剪裁（clip, not mask or filter），非矢量图层覆盖
常规的行政区划剪裁是使用一个中空的多边形做一个遮罩，这种方法的问题是无法实现多种类型图层信息的叠加。
OpenLayer 5提供了几个ol.render类里面的静态函数，用来在canvas上绘制一些要素、几何，利用这个机制，下面实现了一个根据GeoJSON数据进行行政区划剪裁的实例。
代码很简单，一看就懂。
<!doctype html>
<html lang="en">
<!-- 基于olv5.3.0 -->
<head>
<meta charset="utf-8">
<link rel="stylesheet" href="./include/ol.css" type="text/css">
<script src="./include/ol.js" type="text/javascript"></script>
<style type="text/css">
</style>
</head>
<body>
<div id="map"></div>
<script type="text/javascript">
var osm = new ol.layer.Tile({
source: new ol.source.XYZ({
url: 'http://www.google.cn/maps/vt?lyrs=m@189&gl=cn&x={x}&y={y}&z={z}'
}),
});
var bing = new ol.layer.Tile({
source: new ol.source.BingMaps({
key: 'As1HiMj1PvLPlqc_gtM7AqZfBL8ZL3VrjaS3zIb22Uvb9WKhuJObROC-qUpa81U5',
imagerySet: 'AerialWithLabels',
})
});
var view = new ol.View({
center: [0, 0],
zoom: 2
})
var map = new ol.Map({
target: 'map',
layers: [
bing,
osm
],
view: view
});
fetch("./data/USA.geojson").then(function (res) {
return res.json();
}).then(function (json) {
var formatGeoJSON = new ol.format.GeoJSON({
featureProjection: "EPSG:3857"
});
var features = formatGeoJSON.readFeatures(json);
var usaGeometry = features[0].getGeometry();
var fExtent = usaGeometry.getExtent();
view.fit(fExtent);
var fillStyle = new ol.style.Fill({
color: [0, 0, 0, 0]
});
var styleVC = new ol.style.Style({
fill: fillStyle
})
//For openlayers v6.0+:
// osm.on('prerender', function (event) {
osm.on('precompose', function (event) {
var ctx = event.context;
var pixelRatio = event.frameState.pixelRatio;
//For openlayers v6.0+:
// var vecCtx = ol.render.getVectorContext(event);
var vecCtx = event.vectorContext;
ctx.save();
vecCtx.setStyle(styleVC);
vecCtx.drawGeometry(usaGeometry);
ctx.lineWidth = 5 * pixelRatio;
ctx.strokeStyle = 'rgba(0,0,0,0.5)';
ctx.stroke();
ctx.clip();
});
//For openlayers v6.0+:
// osm.on('postrender', function (event) {
osm.on('postcompose', function (event) {
var ctx = event.context;
ctx.restore();
});
})
</script>
</body>
</html>
下面是行政区划的数据。
{“type”:“FeatureCollection”,“features”:[
{“type”:“Feature”,“id”:“USA”,“properties”:{“name”:“United States of
America”},“geometry”:{“type”:“MultiPolygon”,“coordinates”:[[[[-155.54211,19.08348],[-155.68817,18.91619],[-155.93665,19.05939],[-155.90806,19.33888],[-156.07347,19.70294],[-156.02368,19.81422],[-155.85008,19.97729],[-155.91907,20.17395],[-155.86108,20.26721],[-155.78505,20.2487],[-155.40214,20.07975],[-155.22452,19.99302],[-155.06226,19.8591],[-154.80741,19.50871],[-154.83147,19.45328],[-155.22217,19.23972],[-155.54211,19.08348]]],[[[-156.07926,20.64397],[-156.41445,20.57241],[-156.58673,20.783],[-156.70167,20.8643],[-156.71055,20.92676],[-156.61258,21.01249],[-156.25711,20.91745],[-155.99566,20.76404],[-156.07926,20.64397]]],[[[-156.75824,21.17684],[-156.78933,21.06873],[-157.32521,21.09777],[-157.25027,21.21958],[-156.75824,21.17684]]],[[[-157.65283,21.32217],[-157.70703,21.26442],[-157.7786,21.27729],[-158.12667,21.31244],[-158.2538,21.53919],[-158.29265,21.57912],[-158.0252,21.71696],[-157.94161,21.65272],[-157.65283,21.32217]]],[[[-159.34512,21.982],[-159.46372,21.88299],[-159.80051,22.06533],[-159.74877,22.1382],[-159.5962,22.23618],[-159.36569,22.21494],[-159.34512,21.982]]],[[[-94.81758,49.38905],[-94.64,48.84],[-94.32914,48.67074],[-93.63087,48.60926],[-92.61,48.45],[-91.64,48.14],[-90.83,48.27],[-89.6,48.01],[-89.272917,48.019808],[-88.378114,48.302918],[-87.439793,47.94],[-86.461991,47.553338],[-85.652363,47.220219],[-84.87608,46.900083],[-84.779238,46.637102],[-84.543749,46.538684],[-84.6049,46.4396],[-84.3367,46.40877],[-84.14212,46.512226],[-84.091851,46.275419],[-83.890765,46.116927],[-83.616131,46.116927],[-83.469551,45.994686],[-83.592851,45.816894],[-82.550925,45.347517],[-82.337763,44.44],[-82.137642,43.571088],[-82.43,42.98],[-82.9,42.43],[-83.12,42.08],[-83.142,41.975681],[-83.02981,41.832796],[-82.690089,41.675105],[-82.439278,41.675105],[-81.277747,42.209026],[-80.247448,42.3662],[-78.939362,42.863611],[-78.92,42.965],[-79.01,43.27],[-79.171674,43.466339],[-78.72028,43.625089],[-77.737885,43.629056],[-76.820034,43.628784],[-76.5,44.018459],[-76.375,44.09631],[-75.31821,44.81645],[-74.867,45.00048],[-73.34783,45.00738],[-71.50506,45.0082],[-71.405,45.255],[-71.08482,45.30524],[-70.66,45.46],[-70.305,45.915],[-69.99997,46.69307],[-69.237216,47.447781],[-68.905,47.185],[-68.23444,47.35486],[-67.79046,47.06636],[-67.79134,45.70281],[-67.13741,45.13753],[-66.96466,44.8097],[-68.03252,44.3252],[-69.06,43.98],[-70.11617,43.68405],[-70.645476,43.090238],[-70.81489,42.8653],[-70.825,42.335],[-70.495,41.805],[-70.08,41.78],[-70.185,42.145],[-69.88497,41.92283],[-69.96503,41.63717],[-70.64,41.475],[-71.12039,41.49445],[-71.86,41.32],[-72.295,41.27],[-72.87643,41.22065],[-73.71,40.931102],[-72.24126,41.11948],[-71.945,40.93],[-73.345,40.63],[-73.982,40.628],[-73.952325,40.75075],[-74.25671,40.47351],[-73.96244,40.42763],[-74.17838,39.70926],[-74.90604,38.93954],[-74.98041,39.1964],[-75.20002,39.24845],[-75.52805,39.4985],[-75.32,38.96],[-75.071835,38.782032],[-75.05673,38.40412],[-75.37747,38.01551],[-75.94023,37.21689],[-76.03127,37.2566],[-75.72205,37.93705],[-76.23287,38.319215],[-76.35,39.15],[-76.542725,38.717615],[-76.32933,38.08326],[-76.989998,38.239992],[-76.30162,37.917945],[-76.25874,36.9664],[-75.9718,36.89726],[-75.86804,36.55125],[-75.72749,35.55074],[-76.36318,34.80854],[-77.397635,34.51201],[-78.05496,33.92547],[-78.55435,33.86133],[-79.06067,33.49395],[-79.20357,33.15839],[-80.301325,32.509355],[-80.86498,32.0333],[-81.33629,31.44049],[-81.49042,30.72999],[-81.31371,30.03552],[-80.98,29.18],[-80.535585,28.47213],[-80.53,28.04],[-80.056539,26.88],[-80.088015,26.205765],[-80.13156,25.816775],[-80.38103,25.20616],[-80.68,25.08],[-81.17213,25.20126],[-81.33,25.64],[-81.71,25.87],[-82.24,26.73],[-82.70515,27.49504],[-82.85526,27.88624],[-82.65,28.55],[-82.93,29.1],[-83.70959,29.93656],[-84.1,30.09],[-85.10882,29.63615],[-85.28784,29.68612],[-85.7731,30.15261],[-86.4,30.4],[-87.53036,30.27433],[-88.41782,30.3849],[-89.18049,30.31598],[-89.593831,30.159994],[-89.413735,29.89419],[-89.43,29.48864],[-89.21767,29.29108],[-89.40823,29.15961],[-89.77928,29.30714],[-90.15463,29.11743],[-90.880225,29.148535],[-91.626785,29.677],[-92.49906,29.5523],[-93.22637,29.78375],[-93.84842,29.71363],[-94.69,29.48],[-95.60026,28.73863],[-96.59404,28.30748],[-97.14,27.83],[-97.37,27.38],[-97.38,26.69],[-97.33,26.21],[-97.14,25.87],[-97.53,25.84],[-98.24,26.06],[-99.02,26.37],[-99.3,26.84],[-99.52,27.54],[-100.11,28.11],[-100.45584,28.69612],[-100.9576,29.38071],[-101.6624,29.7793],[-102.48,29.76],[-103.11,28.97],[-103.94,29.27],[-104.45697,29.57196],[-104.70575,30.12173],[-105.03737,30.64402],[-105.63159,31.08383],[-106.1429,31.39995],[-106.50759,31.75452],[-108.24,31.754854],[-108.24194,31.34222],[-109.035,31.34194],[-111.02361,31.33472],[-113.30498,32.03914],[-114.815,32.52528],[-114.72139,32.72083],[-115.99135,32.61239],[-117.12776,32.53534],[-117.295938,33.046225],[-117.944,33.621236],[-118.410602,33.740909],[-118.519895,34.027782],[-119.081,34.078],[-119.438841,34.348477],[-120.36778,34.44711],[-120.62286,34.60855],[-120.74433,35.15686],[-121.71457,36.16153],[-122.54747,37.55176],[-122.51201,37.78339],[-122.95319,38.11371],[-123.7272,38.95166],[-123.86517,39.76699],[-124.39807,40.3132],[-124.17886,41.14202],[-124.2137,41.99964],[-124.53284,42.76599],[-124.14214,43.70838],[-124.020535,44.615895],[-123.89893,45.52341],[-124.079635,46.86475],[-124.39567,47.72017],[-124.68721,48.184433],[-124.566101,48.379715],[-123.12,48.04],[-122.58736,47.096],[-122.34,47.36],[-122.5,48.18],[-122.84,49],[-120,49],[-117.03121,49],[-116.04818,49],[-113,49],[-110.05,49],[-107.05,49],[-104.04826,48.99986],[-100.65,49],[-97.22872,49.0007],[-95.15907,49],[-95.15609,49.38425],[-94.81758,49.38905]]],[[[-153.006314,57.115842],[-154.00509,56.734677],[-154.516403,56.992749],[-154.670993,57.461196],[-153.76278,57.816575],[-153.228729,57.968968],[-152.564791,57.901427],[-152.141147,57.591059],[-153.006314,57.115842]]],[[[-165.579164,59.909987],[-166.19277,59.754441],[-166.848337,59.941406],[-167.455277,60.213069],[-166.467792,60.38417],[-165.67443,60.293607],[-165.579164,59.909987]]],[[[-171.731657,63.782515],[-171.114434,63.592191],[-170.491112,63.694975],[-169.682505,63.431116],[-168.689439,63.297506],[-168.771941,63.188598],[-169.52944,62.976931],[-170.290556,63.194438],[-170.671386,63.375822],[-171.553063,63.317789],[-171.791111,63.405846],[-171.731657,63.782515]]],[[[-155.06779,71.147776],[-154.344165,70.696409],[-153.900006,70.889989],[-152.210006,70.829992],[-152.270002,70.600006],[-150.739992,70.430017],[-149.720003,70.53001],[-147.613362,70.214035],[-145.68999,70.12001],[-144.920011,69.989992],[-143.589446,70.152514],[-142.07251,69.851938],[-140.985988,69.711998],[-140.985988,69.711998],[-140.992499,66.000029],[-140.99777,60.306397],[-140.012998,60.276838],[-139.039,60.000007],[-138.34089,59.56211],[-137.4525,58.905],[-136.47972,59.46389],[-135.47583,59.78778],[-134.945,59.27056],[-134.27111,58.86111],[-133.355549,58.410285],[-132.73042,57.69289],[-131.70781,56.55212],[-130.00778,55.91583],[-129.979994,55.284998],[-130.53611,54.802753],[-131.085818,55.178906],[-131.967211,55.497776],[-132.250011,56.369996],[-133.539181,57.178887],[-134.078063,58.123068],[-135.038211,58.187715],[-136.628062,58.212209],[-137.800006,58.499995],[-139.867787,59.537762],[-140.825274,59.727517],[-142.574444,60.084447],[-143.958881,59.99918],[-145.925557,60.45861],[-147.114374,60.884656],[-148.224306,60.672989],[-148.018066,59.978329],[-148.570823,59.914173],[-149.727858,59.705658],[-150.608243,59.368211],[-151.716393,59.155821],[-151.859433,59.744984],[-151.409719,60.725803],[-150.346941,61.033588],[-150.621111,61.284425],[-151.895839,60.727198],[-152.57833,60.061657],[-154.019172,59.350279],[-153.287511,58.864728],[-154.232492,58.146374],[-155.307491,57.727795],[-156.308335,57.422774],[-156.556097,56.979985],[-158.117217,56.463608],[-158.433321,55.994154],[-159.603327,55.566686],[-160.28972,55.643581],[-161.223048,55.364735],[-162.237766,55.024187],[-163.069447,54.689737],[-164.785569,54.404173],[-164.942226,54.572225],[-163.84834,55.039431],[-162.870001,55.348043],[-161.804175,55.894986],[-160.563605,56.008055],[-160.07056,56.418055],[-158.684443,57.016675],[-158.461097,57.216921],[-157.72277,57.570001],[-157.550274,58.328326],[-157.041675,58.918885],[-158.194731,58.615802],[-158.517218,58.787781],[-159.058606,58.424186],[-159.711667,58.93139],[-159.981289,58.572549],[-160.355271,59.071123],[-161.355003,58.670838],[-161.968894,58.671665],[-162.054987,59.266925],[-161.874171,59.633621],[-162.518059,59.989724],[-163.818341,59.798056],[-164.662218,60.267484],[-165.346388,60.507496],[-165.350832,61.073895],[-166.121379,61.500019],[-165.734452,62.074997],[-164.919179,62.633076],[-164.562508,63.146378],[-163.753332,63.219449],[-163.067224,63.059459],[-162.260555,63.541936],[-161.53445,63.455817],[-160.772507,63.766108],[-160.958335,64.222799],[-161.518068,64.402788],[-160.777778,64.788604],[-161.391926,64.777235],[-162.45305,64.559445],[-162.757786,64.338605],[-163.546394,64.55916],[-164.96083,64.446945],[-166.425288,64.686672],[-166.845004,65.088896],[-168.11056,65.669997],[-166.705271,66.088318],[-164.47471,66.57666],[-163.652512,66.57666],[-163.788602,66.077207],[-161.677774,66.11612],[-162.489715,66.735565],[-163.719717,67.116395],[-164.430991,67.616338],[-165.390287,68.042772],[-166.764441,68.358877],[-166.204707,68.883031],[-164.430811,68.915535],[-163.168614,69.371115],[-162.930566,69.858062],[-161.908897,70.33333],[-160.934797,70.44769],[-159.039176,70.891642],[-158.119723,70.824721],[-156.580825,71.357764],[-155.06779,71.147776]]]]}}
]}
ol的库文件请自备。
分类导航