Qt Quick MapPolyLine insertCoordinate

Question

I have a PolyLine on my map and want to add a new co-ordinate to it when a user clicks between two existing points.

I can get the click event with:-

 MouseArea {
    id: mouseArea
    anchors.fill: parent
    acceptedButtons: Qt.LeftButton | Qt.RightButton
    onClicked: {
        console.log('LINE');
    }
}

But I cannot figure out how to work out the required index for insertCoordinate() as there does not appear to be a method to get the start/end vertices of the segment clicked. Is this possible?

score 1 · Accepted Answer · answered Mar 01 '17 at 12:11

I had a similar problem. Currently it cannot be done without writing a new Map object type. So I've changed approach completely and done the following:-

stopped using QtLocation for the map as it is too restrictive at present
integrated a WebKit control with Leaflet as the map provider in the browser HTML
used WebChannel and the WebSocketServer to communicate with the map via the javascript API

This has given me all the flexibility I need on the map as Leaflet is easy to configure and extend whilst allowing me to write the rest of the desktop app in Qt

how does this answer the question? – Pa_ May 10 '17 at 11:56 — Pa_, May 10 '17 at 11:56

score 0 · Answer 2 · answered May 22 '20 at 09:55

I've revisited this project and found a way to do it without using Webkit. It is quite involved:-

1) use the click to get a coordinate

var mapCoord = gpxLine.mapToItem(mapView,mouseX,mouseY);
var coord = mapView.toCoordinate(Qt.point(mapCoord.x,mapCoord.y));

2) use this coordinate to iterate through the path and calculate the path line segment that it is closest to

 float distance = 1000000;
    float dx = 0;
    int index = 0;
    float x0 = coordinate.longitude(),
          y0 = coordinate.latitude(),
          x1y1x,
          x1y1y,
          x2y2x,
          x2y2y;

    double A,B,C,D,dot,len_sq,param,xx,yy,d_x,d_y;

    for(int i = 0; i < trackpoints.count() - 1; i++){
        //Distance from line algorithm https://stackoverflow.com/questions/849211/shortest-distance-between-a-point-and-a-line-segment
        x1y1x = trackpoints[i].latlon.longitude();
        x1y1y = trackpoints[i].latlon.latitude();
        x2y2x = trackpoints[i+1].latlon.longitude();
        x2y2y = trackpoints[i+1].latlon.latitude();

        A = x0 - x1y1x;
        B = y0 - x1y1y;
        C = x2y2x - x1y1x;
        D = x2y2y - x1y1y;

        dot = A * C + B * D;
        len_sq = C * C + D * D;
        param = dot /len_sq;

        if(param < 0  || (x1y1x == x2y2x && x1y1y == x2y2y)){
            xx = x1y1x;
            yy = x1y1y;
        } else if ( param > 1 ){
            xx = x2y2x;
            yy = x2y2y;
        } else {
            xx = x1y1x +param * C;
            yy = x1y1y + param * D;
        }

        d_x = x0 - xx;
        d_y = y0 - yy;
        dx = sqrt(d_x * d_x + d_y * d_y);

        if(dx < distance){
            distance = dx;
            index = i;
        }

    }

3) this gives me the index so I can now insert the coordinate at this index

Qt Quick MapPolyLine insertCoordinate

2 Answers2