turf-area
Calculates the total geographical area in meters squared of any GeoJSON object.
<!doctype html>
<html lang="en">
<head>
<link rel="stylesheet" href="https://rawcdn.githack.com/openlayers/openlayers.github.io/master/en/v5.3.0/css/ol.css" type="text/css">
<link rel="stylesheet" href="assets/css/styles.css" type="text/css">
<script src="//cdn.jsdelivr.net/npm/@turf/turf@5/turf.min.js"></script>
<script src="https://rawcdn.githack.com/openlayers/openlayers.github.io/master/en/v5.3.0/build/ol.js"></script>
<script src="assets/js/es6-promise.min.js"></script>
<script src="https://cdn.polyfill.io/v2/polyfill.min.js?features=requestAnimationFrame,Element.prototype.classList,URL,fetch"></script>
<script src="assets/js/helpers.js"></script>
<title>Turf and OpenLayers 3 - Area</title>
</head>
<body>
<div id="map" class="map"></div>
<div id="surface"></div>
<script type="text/javascript">
var surface = document.getElementById('surface');
var not_selected = 'No surface has been selected!';
surface.innerHTML = not_selected;
// Declare a source for polygons
var vectorSourcePolygons = new ol.source.Vector();
var vectorLayerPolygons = new ol.layer.Vector({
source: vectorSourcePolygons,
style: [
new ol.style.Style({
stroke: new ol.style.Stroke({
color: [0, 121, 88, 1],
width: 2
}),
fill: new ol.style.Fill({
color: 'rgba(0, 0, 0, 0)'
})
})
]
});
// Instanciate a map and add layers
var map = new ol.Map({
target: 'map',
layers: [
new ol.layer.Tile({
source: new ol.source.OSM()
}),
vectorLayerPolygons
],
view: new ol.View({
center: ol.proj.transform(
[-1.5603, 47.2383],
'EPSG:4326',
'EPSG:3857'
),
zoom: 11
})
});
var select = new ol.interaction.Select();
select.on('select', function(e) {
var geojson = (new ol.format.GeoJSON()).writeFeatures(select.getFeatures().getArray(), {
featureProjection: 'EPSG:3857'
});
var total_surface = JSON.parse(geojson).features.reduce(function(initial, feature) {
return initial + turf.area(feature);
}, 0);
if (total_surface > 0) {
surface.innerHTML = 'The selected area is ' + Math.round(total_surface) + ' square meters';
} else {
surface.innerHTML = not_selected;
}
});
map.addInteraction(select);
fetch('assets/data/quartiers_nantes.geojson').then(function(response) {
return response.json().then(function(polys_fc) {
console.log(polys_fc);
vectorSourcePolygons.addFeatures(geojsonToFeatures(polys_fc, {
featureProjection: 'EPSG:3857'
}));
});
});
</script>
</body>
</html>