OpenAtlas

@Stefan Eichert: you already have something like this implemented in THANADOS. Can you give us any pointers?

//**select overlapping polygons on click**//
///////////////////////////////////////////////
function polygonSelect() {
    //define layergroup for selected polygons
    selectedpolys = new L.LayerGroup();
    selectedpolys.addTo(map);

    //layergroup for highlighting on popup hover
    hoverPolys = new L.LayerGroup();
    hoverPolys.addTo(map);

//define invisible marker
    invisIcon = L.icon({
        iconUrl: '/static/images/icons/burial.png',
        iconSize: [1, 1] // size of the icon
    });

//function to get coordinates of clicked position and loop through polygons for matches
    map.on('click', function (e) {
        //set invisible marker and remove invisible marker and popupconent if exists
        if (typeof (newMarker) !== 'undefined') {
            map.removeLayer(newMarker);
        }
        popupContent = '';
        newMarker = new L.marker(e.latlng, {icon: invisIcon}); //global to have it for further use

        //clear previous polygons
        selectedpolys.clearLayers();
        selectedIDs = [];

        //loop through polygons and set matches
        var polys = L.geoJSON(mypolyjson, {
            onEachFeature: function (feature, layer) {
                isMarkerInsidePolygon(newMarker, layer)
            }
        });

        //set popup content to matching polygons for invisible marker
        if (selectedIDs.length !== 0) {
            newMarker.addTo(map);
            newMarker.bindPopup(popupContent).openPopup();
            if (typeof (oldcollapsediv) !== 'undefined') {
                $('#collapseg' + oldcollapsediv).collapse('hide');
                var down = ($('#btn' + oldcollapsediv).hasClass("fa-chevron-down"));
                if (down)
                    $('#btn' + oldcollapsediv).removeClass('fa-chevron-down').addClass('fa-chevron-right');
            }
        }
    });
}

//check if marker is inside polygon and return values
function isMarkerInsidePolygon(checkmarker, poly) {
    if (poly.feature.geometry.type === "Polygon") {
        var inside = false;
        var x = checkmarker.getLatLng().lat, y = checkmarker.getLatLng().lng; //uses the global
        for (var ii = 0; ii < poly.getLatLngs().length; ii++) {
            var polyPoints = poly.getLatLngs()[ii];
            for (var i = 0, j = polyPoints.length - 1; i < polyPoints.length; j = i++) {
                var xi = polyPoints[i].lat, yi = polyPoints[i].lng;
                var xj = polyPoints[j].lat, yj = polyPoints[j].lng;
                var intersect = ((yi > y) != (yj > y))
                    && (x < (xj - xi) * (y - yi) / (yj - yi) + xi);
                if (intersect)
                    inside = !inside;
            }
        }
        if (inside) {
            var mypopupLine =
                JSON.parse('{"id":"' + poly.feature.id + '"' +
                    ', "name":"' + poly.feature.properties.name + '"' +
                    ', "type":"' + poly.feature.properties.maintype.name + '"}');
            selectedIDs.push(mypopupLine);
            var popupLine =
                '<a id="' + poly.feature.id + '"' +
                ' onclick="modalset(this.id)" ' +
                ' onmouseout="hoverPolys.clearLayers()"' +
                ' onmouseover="HoverId = this.id; hoverPoly()"' +
                ' href="#"><p><b>' + poly.feature.properties.name + ' </b>' +
                '(' + poly.feature.properties.maintype.name + ')</p></a>';
            popupContent += popupLine;
            var selectedpoly = L.polygon(polyPoints, SelectionStyle);
            selectedpolys.addLayer(selectedpoly);
        }
        return inside;
    }
}

//add the respective polygon if hovered over popup link
function hoverPoly() {
    hoverPolys.clearLayers();
    hoverGraves = L.geoJSON(mypolyjson, {
        filter: hoverFilter,
        style: HoverStyle
    });
    hoverPolys.addLayer(hoverGraves);
}

//filter to check whether it is the matching polygon
function hoverFilter(feature) {
    if (feature.id == HoverId) {
        return true
    }
}