Display line that crosses 180th meridian | UNL Map JS Docs

Draw a line across the 180th meridian using a GeoJSON source.

Note

If you want to test this example, edit it in JSFiddle or CodePen and replace the "YOUR-OWN-API-KEY" and "YOUR-OWN-VPM-ID" placeholders with your actual api key and vpm id.

<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<title>Display line that crosses 180th meridian</title>
<meta name="viewport" content="initial-scale=1,maximum-scale=1,user-scalable=no" />
<script src="https://unpkg.com/unl-map-js@0.1.5/lib/unl-map-js.js"></script>
<link href="https://unpkg.com/unl-map-js@0.1.5/lib/unl-map-js.css" rel="stylesheet" />
<link
href="https://unpkg.com/maplibre-gl@2.1.9/dist/maplibre-gl.css"
rel="stylesheet"
/>
<style>
	body { margin: 0; padding: 0; }
	#map { position: absolute; top: 0; bottom: 0; width: 100%; }
</style>
</head>
<body>
<div id="map"></div>
<script>
var map = new UnlSdk.Map({
container: "map",
apiKey: "YOUR-OWN-API-KEY",
vpmId: "YOUR-OWN-VPM-ID",
center: [-41.62667, 26.11598],
zoom: 0,
});
 
map.on("load", function () {
map.addLayer({
id: "route",
type: "line",
source: {
type: "geojson",
data: {
type: "Feature",
properties: {},
geometry: createGeometry(false),
},
},
layout: { "line-cap": "round" },
paint: {
"line-color": "#007296",
"line-width": 4,
},
});
 
map.addLayer({
id: "route-label",
type: "symbol",
source: "route",
layout: {
"symbol-placement": "line-center",
"text-field": "Crosses the world",
"text-font": ["Fira GO Regular"],
},
});
 
map.addLayer({
id: "route-two",
type: "line",
source: {
type: "geojson",
data: {
type: "Feature",
properties: {},
geometry: createGeometry(true),
},
},
layout: { "line-cap": "round" },
paint: {
"line-color": "#F06317",
"line-width": 4,
},
});
 
map.addLayer({
id: "route-two-label",
type: "symbol",
source: "route-two",
layout: {
"symbol-placement": "line-center",
"text-field": "Crosses 180th meridian",
"text-font": ["Fira GO Regular"],
},
});
 
function createGeometry(doesCrossAntimeridian) {
var geometry = {
type: "LineString",
coordinates: [
[-72.42187, -16.59408],
[140.27343, 35.67514],
],
};
 
// To draw a line across the 180th meridian,
// if the longitude of the second point minus
// the longitude of original (or previous) point is >= 180,
// subtract 360 from the longitude of the second point.
// If it is less than 180, add 360 to the second point.
 
if (doesCrossAntimeridian) {
var startLng = geometry.coordinates[0][0];
var endLng = geometry.coordinates[1][0];
 
if (endLng - startLng >= 180) {
geometry.coordinates[1][0] -= 360;
} else if (endLng - startLng < 180) {
geometry.coordinates[1][0] += 360;
}
}
 
return geometry;
}
});
</script>
 
</body>
</html>