mirror of
https://github.com/flatgeobuf/flatgeobuf.git
synced 2025-12-08 19:06:03 +00:00
145 lines
6.0 KiB
HTML
145 lines
6.0 KiB
HTML
<html>
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<head>
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<link rel="stylesheet" href="https://unpkg.com/leaflet@1.9.4/dist/leaflet.css" />
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<link rel="stylesheet" href="/examples/site.css" />
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<script src="https://unpkg.com/underscore@1.13.1/underscore-min.js"></script>
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<script src="https://unpkg.com/leaflet@1.9.4/dist/leaflet.js"></script>
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<script src="https://unpkg.com/flatgeobuf@4.3.3/dist/flatgeobuf-geojson.min.js"></script>
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<script src="https://unpkg.com/json-formatter-js@2.5.23/dist/json-formatter.umd.js"></script>
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<style>
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#map { height: 480px; }
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</style>
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</head>
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<body>
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<ul class="primary-navigation">
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<li class="active">
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Leaflet Example
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</li>
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<li>
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<a href="/examples/openlayers/filtered.html">OpenLayers Example</a>
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</li>
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<li>
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<a href="/examples/maplibre/">MapLibre Example</a>
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</li>
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</ul>
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<ul class="secondary-navigation">
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<li><a href="/examples/leaflet/">Basic Example</a></li>
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<li class="active">Filter By Rect</li>
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<li><a href="/examples/leaflet/large.html">Filtering a Large Dataset</a></li>
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</ul>
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<div id="map"></div>
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<script>
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document.addEventListener("DOMContentLoaded", async () => {
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// basic OSM Leaflet map
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const map = L.map('map').setView([39, -104], 6);
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L.tileLayer('https://{s}.tile.openstreetmap.org/{z}/{x}/{y}.png', {
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maxZoom: 19,
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attribution: '© <a href="https://www.openstreetmap.org/copyright">OpenStreetMap</a> contributors'
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}).addTo(map);
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// optionally show some meta-data about the FGB file
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function handleHeaderMeta(headerMeta) {
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const header = document.getElementById('header')
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const formatter = new JSONFormatter(headerMeta, 10)
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header.appendChild(formatter.render())
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}
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// For the example, we fix a visible Rect representing the query
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// bounding box in the middle of the map
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function getBoundForRect() {
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const widthMeters = 500000;
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return map.getCenter().toBounds(widthMeters);
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}
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// convert the rect into the format flatgeobuf expects
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function fgBoundingBox() {
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const bounds = getBoundForRect();
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return {
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minX: bounds.getWest(),
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minY: bounds.getSouth(),
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maxX: bounds.getEast(),
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maxY: bounds.getNorth(),
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};
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}
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// track the previous results so we can remove them when adding new results
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let previousResults = L.layerGroup().addTo(map);
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async function updateResults() {
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// remove the old results
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previousResults.remove();
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const nextResults = L.layerGroup().addTo(map);
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previousResults = nextResults;
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// Use flatgeobuf JavaScript API to iterate features as geojson.
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// Because we specify a bounding box, flatgeobuf will only fetch the relevant subset of data,
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// rather than the entire file.
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const iter = flatgeobuf.deserialize('/test/data/UScounties.fgb', fgBoundingBox(), handleHeaderMeta);
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for await (const feature of iter) {
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const defaultStyle = {
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color: 'blue',
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weight: 2,
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fillOpacity: 0.1,
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};
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L.geoJSON(feature, {
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style: defaultStyle,
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}).on({
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'mouseover': (e) => {
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const layer = e.target;
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layer.setStyle({
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color: 'blue',
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weight: 4,
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fillOpacity: 0.7,
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});
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layer.bringToFront();
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},
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'mouseout': (e) => {
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const layer = e.target;
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layer.setStyle(defaultStyle);
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}
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}).bindPopup(`<h1>${feature.properties.NAME} ${feature.properties.LSAD}, ${feature.properties.STATE}</h1>`)
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.addTo(nextResults);
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}
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}
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// if the user is panning around alot, only update once per second max
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const updateResultsThrottled = _.throttle(updateResults, 1000);
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// show a leaflet rect corresponding to our bounding box
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const rectangle = L.rectangle(getBoundForRect(), { color: "yellow", fillOpacity: 0.7, opacity: 1.0 }).addTo(map);
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// show results based on the initial map
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updateResultsThrottled();
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// ...and update the results whenever the map moves
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map.on("moveend", ()=> {
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rectangle.setBounds(getBoundForRect());
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updateResultsThrottled();
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});
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});
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</script>
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<p>
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FlatGeobuf's spatial index allows you to fetch the features that
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intersect a given bounding box, without downloading the entire file.
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This can be helpful when you have a very large file but are only
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interested in a small portion of it, and want to keep your page loads
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small and fast.
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</p>
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<p>
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For the purposes of the example we've highlighted our bounding box in
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yellow. Pan the map to move the query's bounding box.
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</p>
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<p>
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Open your developer console's network pane, and inspect the network
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traffic. Compared to the <a href="/examples/leaflet/">example which loads the entire file</a>,
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you'll see that this example makes more requests for the .fgb file, but
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they are much smaller because we fetch only the relevant sections of
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the file.
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</p>
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<div id="header">
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<h3>Parsed header content</h3>
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</div>
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</body>
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</html>
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