[Interest] QtLocation MapPolyLine and MouseArea

maitai maitai at virtual-winds.org
Thu Mar 7 21:35:21 CET 2019

Yes thanks I know the maths for that, the problem being it's going to be 
calculated for all lines every time the user touches the mouse.

Just to share here is my routine to calculate a QPointF distance to a 

#define DIST(P1, P2) ((P1.x() - P2.x()) * (P1.x() - P2.x()) + (P1.y() - 
P2.y()) * (P1.y() - P2.y()))

double Util::distToSegment(const QPointF &point,const QLineF &line)
     const double d1 = DIST(line.p1(),line.p2());
     if(d1 == 0.0)
         return qSqrt(DIST(point, line.p1()));
     const double t = ((point.x() - line.p1().x()) * (line.p2().x() - 
               + (point.y() - line.p1().y()) * (line.p2().y() - 
line.p1().y())) / d1;
     if(t < 0)
         return qSqrt(DIST(point, line.p1()));
         return qSqrt(DIST(point, line.p2()));
     return qSqrt(DIST(point, QPointF(line.p1().x() + t * (line.p2().x() 
- line.p1().x()),
                                    line.p1().y() + t * (line.p2().y() - 

I doubt there is a faster solution, still it's heavy if you need to do 
that on each mouse move, for all lines/segments you need to iterate to 
find the smallest.

Philippe Lelong

Le 07-03-2019 20:28, Jérôme Godbout a écrit :
> Just throwing an idea, maybe you could convert the mouse click or
> hover to coordinate on the Map::toCoordinate() and interpolate the
> coordinate to see with parameter to the line vector and then find the
> distance to that line parameter point or min/max point. This is not
> super fast but could be quick enough. Maybe doing the inverted
> converting the coordinate to point would make the computation easier.
> http://mathworld.wolfram.com/Point-LineDistance2-Dimensional.html
> -----Original Message-----
> From: Interest <interest-bounces at qt-project.org> On Behalf Of maitai
> Sent: March 7, 2019 12:33 PM
> To: Interest at qt-project.org
> Subject: [Interest] QtLocation MapPolyLine and MouseArea
> Hi,
> I need to trigger various actions whenever a MapPolyLine is hovered or
> pressed, such as displaying a tooltip, a menu, etc.
> I have put a MouseArea on it with anchors.fills: parent, but the
> problem is that the mouse area does not represent the line, but the
> polygon made by the line. For instance if you have a L shape, entered
> event and so on is triggered when you enter the bounding rectangle of
> the line, not when you hover over the line itself.
> On a QGraphicsScene we had the shape() protected method for that kinds
> of case, for instance with a QPainterPathStroker to give some
> thickness to the line's "mousearea".
> I will probably end with a custom property that will carry the pixel
> distance between the line segments and the mouse coordinates, but this
> is going to be heavy to compute (I have potentially hundreds of
> complicated lines on the map).
> Is there a better way or even better a standard way to do that?
> Thanks
> Philippe Lelong
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