Rohan Rohan - 27 days ago 18
Javascript Question

How to calculate the distance of a polyline in Leaflet like geojson.io?

I am working on a map with Mapbox and Leaflet and I am supposed to let the user draw polygons and calculate and show the are of that polygon and I also need to let the user draw a polyline and show the distance of the polyline.

I have figured out the polygon area feature but I cannot figure out how to calculate the distance of a polyline.

My code is as follows:

loadScript('https://api.tiles.mapbox.com/mapbox.js/plugins/leaflet-draw/v0.2.2/leaflet.draw.js', function(){
loadScript('https://api.tiles.mapbox.com/mapbox.js/plugins/leaflet-geodesy/v0.1.0/leaflet-geodesy.js', function(){
var featureGroup = L.featureGroup().addTo(map);

var drawControl = new L.Control.Draw({
edit: {
featureGroup: featureGroup
},
draw: {
polygon: true,
polyline: true,
rectangle: false,
circle: false,
marker: false
}
}).addTo(map);

map.on('draw:created', showPolygonArea);
map.on('draw:edited', showPolygonAreaEdited);

function showPolygonAreaEdited(e) {
e.layers.eachLayer(function(layer) {
showPolygonArea({ layer: layer });
});
}
function showPolygonArea(e) {
var type = e.layerType,
layer = e.layer;

if (type === 'polygon') {
featureGroup.clearLayers();
featureGroup.addLayer(e.layer);
e.layer.bindPopup(((LGeo.area(e.layer) / 1000000) * 0.62137).toFixed(2) + ' mi<sup>2</sup>');
e.layer.openPopup();
}

if (type === 'polyline') {
featureGroup.clearLayers();
featureGroup.addLayer(e.layer);
// What do I do different here to calculate the distance of the polyline?
// Is there a method in the LGeo lib itself?
// e.layer.bindPopup(((LGeo.area(e.layer) / 1000000) * 0.62137).toFixed(2) + ' mi<sup>2</sup>');
e.layer.openPopup();
}

}
});
});


Is there a method in the LGeo lib itself which will help me calculate the distance of the polyline? The devs at geogson.io also have a way to calculate the distance but I cannot seem to figure it out looking at their code. I am not a seasoned Javascript developer. Any help is welcome. :)

Answer

So I finally came up with an algorithm myself. I basically found the property of the polyline which holds all the latlngs of the polyline and then I made it go through a loop and I used the distanceTo method from Leaflet to calculate distance between points and kept on adding them to a totalDistance variable.

if (type === 'polyline') {
    featureGroup.clearLayers();
    featureGroup.addLayer(e.layer);

    // Calculating the distance of the polyline
    var tempLatLng = null;
    var totalDistance = 0.00000;
    $.each(e.layer._latlngs, function(i, latlng){
        if(tempLatLng == null){
            tempLatLng = latlng;
            return;
        }

        totalDistance += tempLatLng.distanceTo(latlng);
        tempLatLng = latlng;
    });
    e.layer.bindPopup((totalDistance).toFixed(2) + ' meters');
    e.layer.openPopup();
}
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