栅格重投影【译】

原文链接及内容

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

演示不同投影之间的栅格重投影。

main.js代码如下：

import Map from 'ol/Map.js';
import TileGrid from 'ol/tilegrid/TileGrid.js';
import TileLayer from 'ol/layer/Tile.js';
import View from 'ol/View.js';
import WMTS, {optionsFromCapabilities} from 'ol/source/WMTS.js';
import WMTSCapabilities from 'ol/format/WMTSCapabilities.js';
import proj4 from 'proj4';
import {OSM, TileImage, TileWMS} from 'ol/source.js';
import {createXYZ} from 'ol/tilegrid.js';
import {getCenter, getWidth} from 'ol/extent.js';
import {get as getProjection, transformExtent} from 'ol/proj.js';
import {register} from 'ol/proj/proj4.js';

proj4.defs(
  'EPSG:27700',
  '+proj=tmerc +lat_0=49 +lon_0=-2 +k=0.9996012717 ' +
    '+x_0=400000 +y_0=-100000 +ellps=airy ' +
    '+towgs84=446.448,-125.157,542.06,0.15,0.247,0.842,-20.489 ' +
    '+units=m +no_defs'
);
proj4.defs(
  'EPSG:23032',
  '+proj=utm +zone=32 +ellps=intl ' +
    '+towgs84=-87,-98,-121,0,0,0,0 +units=m +no_defs'
);
proj4.defs(
  'EPSG:5479',
  '+proj=lcc +lat_1=-76.66666666666667 +lat_2=' +
    '-79.33333333333333 +lat_0=-78 +lon_0=163 +x_0=7000000 +y_0=5000000 ' +
    '+ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs'
);
proj4.defs(
  'EPSG:21781',
  '+proj=somerc +lat_0=46.95240555555556 ' +
    '+lon_0=7.439583333333333 +k_0=1 +x_0=600000 +y_0=200000 +ellps=bessel ' +
    '+towgs84=674.4,15.1,405.3,0,0,0,0 +units=m +no_defs'
);
proj4.defs(
  'EPSG:3413',
  '+proj=stere +lat_0=90 +lat_ts=70 +lon_0=-45 +k=1 ' +
    '+x_0=0 +y_0=0 +datum=WGS84 +units=m +no_defs'
);
proj4.defs(
  'EPSG:2163',
  '+proj=laea +lat_0=45 +lon_0=-100 +x_0=0 +y_0=0 ' +
    '+a=6370997 +b=6370997 +units=m +no_defs'
);
proj4.defs(
  'ESRI:54009',
  '+proj=moll +lon_0=0 +x_0=0 +y_0=0 +datum=WGS84 ' + '+units=m +no_defs'
);
register(proj4);

const proj27700 = getProjection('EPSG:27700');
proj27700.setExtent([-650000, -150000, 1350000, 1450000]);

const proj23032 = getProjection('EPSG:23032');
proj23032.setExtent([-1206118.71, 4021309.92, 1295389.0, 8051813.28]);

const proj5479 = getProjection('EPSG:5479');
proj5479.setExtent([6825737.53, 4189159.8, 9633741.96, 5782472.71]);

const proj21781 = getProjection('EPSG:21781');
proj21781.setExtent([485071.54, 75346.36, 828515.78, 299941.84]);

const proj3413 = getProjection('EPSG:3413');
proj3413.setExtent([-4194304, -4194304, 4194304, 4194304]);

const proj2163 = getProjection('EPSG:2163');
proj2163.setExtent([-8040784.5135, -2577524.921, 3668901.4484, 4785105.1096]);

const proj54009 = getProjection('ESRI:54009');
proj54009.setExtent([-18e6, -9e6, 18e6, 9e6]);

const layers = {};

layers['osm'] = new TileLayer({
  source: new OSM(),
});

layers['wms4326'] = new TileLayer({
  source: new TileWMS({
    url: 'https://ahocevar.com/geoserver/gwc/service/wms',
    crossOrigin: '',
    params: {
      'LAYERS': 'ne:NE1_HR_LC_SR_W_DR',
      'TILED': true,
      'VERSION': '1.1.1',
    },
    projection: 'EPSG:4326',
    // Source tile grid (before reprojection)
    tileGrid: createXYZ({
      extent: [-180, -90, 180, 90],
      maxResolution: 360 / 512,
      maxZoom: 10,
    }),
    // Accept a reprojection error of 2 pixels
    reprojectionErrorThreshold: 2,
  }),
});

layers['wms21781'] = new TileLayer({
  source: new TileWMS({
    attributions:
      '© <a href="https://shop.swisstopo.admin.ch/en/products/maps/national/lk1000"' +
      'target="_blank">Pixelmap 1:1000000 / geo.admin.ch</a>',
    crossOrigin: 'anonymous',
    params: {
      'LAYERS': 'ch.swisstopo.pixelkarte-farbe-pk1000.noscale',
      'FORMAT': 'image/jpeg',
    },
    url: 'https://wms.geo.admin.ch/',
    projection: 'EPSG:21781',
  }),
});

const parser = new WMTSCapabilities();

layers['wmts3413'] = new TileLayer();
const urlA =
  'https://map1.vis.earthdata.nasa.gov/wmts-arctic/' +
  'wmts.cgi?SERVICE=WMTS&request=GetCapabilities';
fetch(urlA)
  .then(function (response) {
    return response.text();
  })
  .then(function (text) {
    const result = parser.read(text);
    const options = optionsFromCapabilities(result, {
      layer: 'OSM_Land_Mask',
      matrixSet: 'EPSG3413_250m',
    });
    options.crossOrigin = '';
    options.projection = 'EPSG:3413';
    options.wrapX = false;
    layers['wmts3413'].setSource(new WMTS(options));
  });

layers['bng'] = new TileLayer();
const urlB =
  'https://tiles.arcgis.com/tiles/qHLhLQrcvEnxjtPr/arcgis/rest/services/OS_Open_Raster/MapServer/WMTS';
fetch(urlB)
  .then(function (response) {
    return response.text();
  })
  .then(function (text) {
    const result = parser.read(text);
    const options = optionsFromCapabilities(result, {
      layer: 'OS_Open_Raster',
    });
    options.attributions =
      'Contains OS data © Crown Copyright and database right ' +
      new Date().getFullYear();
    options.crossOrigin = '';
    options.projection = 'EPSG:27700';
    options.wrapX = false;
    layers['bng'].setSource(new WMTS(options));
  });

const startResolution = getWidth(getProjection('EPSG:3857').getExtent()) / 256;
const resolutions = new Array(22);
for (let i = 0, ii = resolutions.length; i < ii; ++i) {
  resolutions[i] = startResolution / Math.pow(2, i);
}

layers['states'] = new TileLayer({
  source: new TileWMS({
    url: 'https://ahocevar.com/geoserver/wms',
    crossOrigin: '',
    params: {'LAYERS': 'topp:states'},
    serverType: 'geoserver',
    tileGrid: new TileGrid({
      extent: [-13884991, 2870341, -7455066, 6338219],
      resolutions: resolutions,
      tileSize: [512, 256],
    }),
    projection: 'EPSG:3857',
  }),
});

const map = new Map({
  layers: [layers['osm'], layers['bng']],
  target: 'map',
  view: new View({
    projection: 'EPSG:3857',
    center: [0, 0],
    zoom: 2,
  }),
});

const baseLayerSelect = document.getElementById('base-layer');
const overlayLayerSelect = document.getElementById('overlay-layer');
const viewProjSelect = document.getElementById('view-projection');
const renderEdgesCheckbox = document.getElementById('render-edges');
let renderEdges = false;

function updateViewProjection() {
  const newProj = getProjection(viewProjSelect.value);
  const newProjExtent = newProj.getExtent();
  const newView = new View({
    projection: newProj,
    center: getCenter(newProjExtent || [0, 0, 0, 0]),
    zoom: 0,
    extent: newProjExtent || undefined,
  });
  map.setView(newView);

  // Example how to prevent double occurrence of map by limiting layer extent
  if (newProj.isGlobal()) {
    layers['bng'].setExtent(
      transformExtent(proj27700.getExtent(), proj27700, newProj, 2)
    );
  } else {
    layers['bng'].setExtent(undefined);
  }
}

/**
 * Handle change event.
 */
viewProjSelect.onchange = function () {
  updateViewProjection();
};

updateViewProjection();

const updateRenderEdgesOnLayer = function (layer) {
  if (layer instanceof TileLayer) {
    const source = layer.getSource();
    if (source instanceof TileImage) {
      source.setRenderReprojectionEdges(renderEdges);
    }
  }
};

/**
 * Handle change event.
 */
baseLayerSelect.onchange = function () {
  const layer = layers[baseLayerSelect.value];
  if (layer) {
    layer.setOpacity(1);
    updateRenderEdgesOnLayer(layer);
    map.getLayers().setAt(0, layer);
  }
};

/**
 * Handle change event.
 */
overlayLayerSelect.onchange = function () {
  const layer = layers[overlayLayerSelect.value];
  if (layer) {
    layer.setOpacity(0.7);
    updateRenderEdgesOnLayer(layer);
    map.getLayers().setAt(1, layer);
  }
};

/**
 * Handle change event.
 */
renderEdgesCheckbox.onchange = function () {
  renderEdges = renderEdgesCheckbox.checked;
  map.getLayers().forEach(function (layer) {
    updateRenderEdgesOnLayer(layer);
  });
};

界面布局文件index.html代码如下：

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8">
    <title>Raster Reprojection</title>
    <link rel="stylesheet" href="node_modules/ol/ol.css">
    <style>
      .map {
        width: 100%;
        height: 400px;
      }
      .reprojection-form {
        display: grid;
        grid-template-columns: max-content max-content;
        grid-gap: 5px;
        gap: 5px;
      }
    </style>
  </head>
  <body>
    <div id="map" class="map"></div>
    <form class="reprojection-form">
      <label for="base-layer">Base map:</label>
      <select id="base-layer">
        <option value="osm">OSM (EPSG:3857)</option>
        <option value="wms4326">WMS (EPSG:4326)</option>
      </select>

      <label for="overlay-layer">Overlay map:</label>
      <select id="overlay-layer">
        <option value="bng">British National Grid (EPSG:27700)</option>
        <option value="wms21781">Swisstopo WMS (EPSG:21781)</option>
        <option value="wmts3413">NASA Arctic WMTS (EPSG:3413)</option>
        <option value="states">United States (EPSG:3857)</option>
      </select>

      <label for="view-projection">View projection:</label>
      <select id="view-projection">
        <option value="EPSG:3857">Spherical Mercator (EPSG:3857)</option>
        <option value="EPSG:4326">WGS 84 (EPSG:4326)</option>
        <option value="ESRI:54009">Mollweide (ESRI:54009)</option>
        <option value="EPSG:27700">British National Grid (EPSG:27700)</option>
        <option value="EPSG:23032">ED50 / UTM zone 32N (EPSG:23032)</option>
        <option value="EPSG:2163">US National Atlas Equal Area (EPSG:2163)</option>
        <option value="EPSG:3413">NSIDC Polar Stereographic North (EPSG:3413)</option>
        <option value="EPSG:5479">RSRGD2000 / MSLC2000 (EPSG:5479)</option>
      </select>

      <label for="render-edges">Render reprojection edges:</label>
      <span><input type="checkbox" id="render-edges" /></span>
    </form>
    <!-- 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>