98 lines
3.0 KiB
JavaScript
98 lines
3.0 KiB
JavaScript
// NOCOMPILE
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// this example uses d3 for which we don't have an externs file.
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goog.require('ol');
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goog.require('ol.Map');
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goog.require('ol.View2D');
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goog.require('ol.extent');
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goog.require('ol.layer.Image');
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goog.require('ol.layer.Tile');
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goog.require('ol.proj');
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goog.require('ol.source.ImageCanvas');
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goog.require('ol.source.Stamen');
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var map = new ol.Map({
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layers: [
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new ol.layer.Tile({
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source: new ol.source.Stamen({
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layer: 'watercolor'
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})
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})
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],
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renderers: ['canvas'],
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target: 'map',
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view: new ol.View2D({
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center: ol.proj.transform([-97, 38], 'EPSG:4326', 'EPSG:3857'),
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zoom: 4
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})
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});
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/**
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* Load the topojson data and create an ol.layer.Image for that data.
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*/
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d3.json('data/us.json', function(error, us) {
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var features = topojson.feature(us, us.objects.counties);
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/**
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* This function uses d3 to render the topojson features to a canvas.
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* @param {ol.Extent} extent Extent.
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* @param {number} resolution Resolution.
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* @param {number} pixelRatio Pixel ratio.
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* @param {ol.Size} size Size.
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* @param {ol.proj.Projection} projection Projection.
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* @return {HTMLCanvasElement}
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*/
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var canvasFunction = function(extent, resolution, pixelRatio,
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size, projection) {
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var canvasWidth = size[0];
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var canvasHeight = size[1];
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var canvas = d3.select(document.createElement('canvas'));
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canvas.attr('width', canvasWidth).attr('height', canvasHeight);
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var context = canvas.node().getContext('2d');
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var d3Projection = d3.geo.mercator().scale(1).translate([0, 0]);
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var d3Path = d3.geo.path().projection(d3Projection);
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var pixelBounds = d3Path.bounds(features);
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var pixelBoundsWidth = pixelBounds[1][0] - pixelBounds[0][0];
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var pixelBoundsHeight = pixelBounds[1][1] - pixelBounds[0][1];
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var geoBounds = d3.geo.bounds(features);
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var geoBoundsLeftBottom = ol.proj.transform(
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geoBounds[0], 'EPSG:4326', projection);
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var geoBoundsRightTop = ol.proj.transform(
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geoBounds[1], 'EPSG:4326', projection);
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var geoBoundsWidth = geoBoundsRightTop[0] - geoBoundsLeftBottom[0];
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if (geoBoundsWidth < 0) {
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geoBoundsWidth += ol.extent.getWidth(projection.getExtent());
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}
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var geoBoundsHeight = geoBoundsRightTop[1] - geoBoundsLeftBottom[1];
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var widthResolution = geoBoundsWidth / pixelBoundsWidth;
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var heightResolution = geoBoundsHeight / pixelBoundsHeight;
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var r = Math.max(widthResolution, heightResolution);
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var scale = r / (resolution / pixelRatio);
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var center = ol.proj.transform(ol.extent.getCenter(extent),
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projection, 'EPSG:4326');
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d3Projection.scale(scale).center(center)
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.translate([canvasWidth / 2, canvasHeight / 2]);
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d3Path = d3Path.projection(d3Projection).context(context);
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d3Path(features);
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context.stroke();
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return canvas[0][0];
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};
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var layer = new ol.layer.Image({
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source: new ol.source.ImageCanvas({
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canvasFunction: canvasFunction,
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projection: 'EPSG:3857'
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})
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});
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map.addLayer(layer);
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});
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