turf-combine
Combines a FeatureCollection of point, linestring, or polygon Features into multipoint, multilinestring, or multipolygon Features.
<!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 - combine</title>
</head>
<body>
<div id="map" class="map"></div>
<button id="switchlayer" type="button">Show sovereignty</button>
<script type="text/javascript">
// 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
})
})
]
});
var select = new ol.interaction.Select();
// 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.fromLonLat([-1.5603, 47.2383]),
zoom: 2
})
});
map.addInteraction(select);
var multis = ['MultiPoint', 'MultiLineString', 'MultiPolygon'];
var polygons;
fetch('assets/data/countries.json').then(function(response) {
return response.json().then(function(polys_fc) {
polygons = polys_fc;
var groups = polys_fc.features.reduce(function(prev, curr) {
var key = curr.properties.SOVEREIGNT;
if (Object.keys(prev).indexOf(key) === -1) {
prev[key] = [];
}
// We split Multi because turf.combine need
// Point, LineString or Polygon for input
if (multis.indexOf(curr.geometry.type) !== -1) {
var featuresArray = curr.geometry.coordinates.map(function(coord) {
return {
"type": "Feature",
"properties": curr.properties,
"geometry": {
"type": curr.geometry.type.replace('Multi', ''),
"coordinates": coord
}
};
});
prev[key] = prev[key].concat(featuresArray);
} else {
prev[key].push(curr);
}
return prev;
}, {});
var multiPolyFeatures = [];
for (k in groups) {
var featureCollectionMulti = turf.combine(turf.featureCollection(groups[k]));
var props = featureCollectionMulti.features[0].properties;
props.collectedProperties[0].parts = props.collectedProperties.length;
props = props.collectedProperties[0];
featureCollectionMulti.features[0].properties = props;
multiPolyFeatures.push(featureCollectionMulti.features[0]);
}
multiPolyFeatures.sort(function(a, b) {
return b.properties.parts - a.properties.parts;
});
geojsonBySovereignty = turf.featureCollection(multiPolyFeatures);
vectorSourcePolygons.addFeatures(geojsonToFeatures(polys_fc, {
featureProjection: 'EPSG:3857'
}));
});
});
var button = document.getElementById('switchlayer');
button.addEventListener('click', function(e) {
if (this.innerHTML === 'Show sovereignty') {
this.innerHTML = 'Show countries';
vectorSourcePolygons.clear();
vectorSourcePolygons.addFeatures(geojsonToFeatures(geojsonBySovereignty, {
featureProjection: 'EPSG:3857'
}));
} else {
this.innerHTML = 'Show sovereignty';
vectorSourcePolygons.clear();
vectorSourcePolygons.addFeatures(geojsonToFeatures(polygons, {
featureProjection: 'EPSG:3857'
}));
}
});
</script>
</body>
</html>