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

Question

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 1

I solved this by extending L.Polyline class, and using LatLng's distanceTo method:

L.Polyline = L.Polyline.include({
    getDistance: function(system) {
        // distance in meters
        var mDistanse = 0,
            length = this._latlngs.length;
        for (var i = 1; i < length; i++) {
            mDistanse += this._latlngs[i].distanceTo(this._latlngs[i - 1]);
        }
        // optional
        if (system === 'imperial') {
            return mDistanse / 1609.34;
        } else {
            return mDistanse / 1000;
        }
    }
});

Hope it helps someone.

Answer 2

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();
}

Answer 3

And also that's the solution of calculate the area of circle.

else if (type === 'circle') {
     var area = 0;
     var radius = e.layer.getRadius();
     area = (Math.PI) * (radius * radius);
     e.layer.bindPopup((area / 1000000).toFixed(2) + ' km<sup>2</sup>');
     e.layer.openPopup();
}

Answer 4

I would also encourage readers to check out the turf library. It works great with leaflet and has many useful methods including polyline distance. http://turfjs.org/docs