Leaflet - allow user to draw a Polyline with only two points?

Question

Leaflet draw allows users to draw lines on a map. There's an example at https://leaflet.github.io/Leaflet.draw/docs/examples/full.html

I want my users to be able to draw lines consisting of only two points. That is, they click, a marker goes down, they move their mouse, click again, and a line is drawn between the two points.

With the default options, the user has to either click the last point again, or the "finish" button.

Looking at the documentation for Polyline - http://leaflet.github.io/Leaflet.draw/docs/leaflet-draw-latest.html#polylineoptions - there are several options, but none which specify the maximum number of points a line can have.

Is it possible to set a maximum number of nodes for a line? Or to automatically detect when the second point has been drawn?

Answer 1

You can do this using logic with Javascript.

I have written an example quickly bellow on how to do this with comments explaining the resolution process :

// We have the initialisation of the map above

/**
 * We create an object to store the coordinates of the two points
 **/
let coordinates = {
    point1: {
        lat: null,
        lng: null
    },
    point2: {
        lat: null,
        lng: null
    }
}

// Here I created a custom Icon so we can add a custom className to it 
const iconMap = L.icon({
    iconUrl: "https://unpkg.com/[email protected]/dist/images/marker-icon.png",

    iconSize:     [25, 41],
    iconAnchor:   [12, 41],
    popupAnchor:  [1, -34],
    className: 'originMarker'
});

let markerOrigin = null;

function onMapClick(e) {
    if (
            coordinates.point1.lat === null && coordinates.point1.lng === null
        &&  coordinates.point2.lat === null && coordinates.point2.lng === null
    ) {
        coordinates.point1.lat = e.latlng.lat;
        coordinates.point1.lng = e.latlng.lng;

        // We add the marker to the map since it is the first point of the line
        markerOrigin = L.marker(
            [ e.latlng.lat, e.latlng.lng ],
            { icon: iconMap }
        ).addTo(map);
    } else if (
        coordinates.point1.lat !== null
        && coordinates.point1.lng !== null
        && coordinates.point2.lat === null
        && coordinates.point2.lng === null
    ) {
        coordinates.point2.lat = e.latlng.lat;
        coordinates.point2.lng = e.latlng.lng;
        
        // We have enough points (2) to create a line
        const line = [
            [ coordinates.point1.lat, coordinates.point1.lng ],
            [ coordinates.point2.lat, coordinates.point2.lng ]
        ];

        L.polyline(line, {color: 'red'}).addTo(map);
        
        // we remove the marker
        document.getElementsByClassName('originMarker')[0].remove();
    } else {
        coordinates.point1.lat = e.latlng.lat;
        coordinates.point1.lng = e.latlng.lng;

        coordinates.point2.lat = null;
        coordinates.point2.lng = null;

        markerOrigin = L.marker(
            [ e.latlng.lat, e.latlng.lng ],
            { icon: iconMap }
        ).addTo(map);
    }

    console.log(coordinates);
}

// we bind a function to the map to detect the click event
map.on('click', onMapClick);