[Qt-interest] Using Qpainter/Qgraphics for a gps car-like

[Andre Somers]

Gustavo B. Schenkel wrote:
> The problem is the points, they have too much numbers after the 
> dot, in the screen they show all in the same place.
>
> Then i don't know if i need do some calculation to transform this 
> numbers to others.
>
> i am sending my painter code. I am using the setWindow function 
> but i still don't know much about it.
>
> void RenderArea::paintEvent(QPaintEvent * /* event */)
> {
>
>     static const QPointF square[4] = {
>             QPointF(-29.683436, -53.800570),
>             QPointF(-29.683795, -53.799620),
>             QPointF(-29.684242, -53.800749),
>             QPointF(-29.684478, -53.799623)
>         };
>
>
>     QPainter painter(this);
>     painter.setRenderHint(QPainter::Antialiasing, true);
>     painter.setWindow(-33,-57, 10, 10);
>     painter.save();
>     painter.drawPolygon(square, 4);
>     painter.restore();
> }
>
>   
So... are you trying to plot GPS coordinates directly, and expect to see 
something? Realize that one pixel on your screen will end up 
representing an entire degree. In north-south direction, that is 100 
nauticle miles, or about 180 km. In the east/west direction, it depends 
on the latitude. You can see that that's not going to work. You will 
need some kind of map projection. There are many to choose from, 
depending on what features of the map you find most important. None of 
these are available in Qt by default, you'll have to implement them 
yourself. They usually involve a bit of math :-) Perhaps this link will 
get you started: http://en.wikipedia.org/wiki/Map_projection


André