Marble/Runners/VehicleTracking

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Tutorial Series	Marble C++ Tutorial
Previous	Tutorial 12 - Displaying Places the proper way (via GeoDataDocuments)
What's Next	Tutorial 14 - Yet missing
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We want to present you another C++ example of Marble Runnable usage, here on KDE TechBase. It's about the cars. Imaging that there are two completely drunk car drivers. They are driving around ukranian city Kiev (EURO-2012). They are driving circles around it with set radius and speed. At the end of tutorial you will have an application with smth like:

Let's think about implementation a bit:

1. Init MarbleWidget
2. Implement placemarks for cars "Bus" and "Car"
3. Change their coordinates using trigonometry functions
4. Apply new coordinates

As far as you understood, we need to change coordinates with really small interval (~10 ms). In this way, to not block GUI thread we need to use multi-threading. For that we suggest that model:

1. Create QThread #1
2. Create CarWorker #1 (= worker for cars' coordinates)
3. Move CarWorker #1 into thread #1
4. The same for Car #2 (1-3)

Then we will have three threads - GUI, Calculations #1, Calculations #2. To connect calc. threads with GUI we should use Qt S/S (Signal/Slot) connection.

Important

Use here connection type Qt::BlockingQueuedConnection, another way GUI thread will be blocked

Now we have nice implementation plan, let's start coding. The code listed under this text is doing:

1. main() creates object of the Window (our main QWidget-based window)
2. Window creates the MarbleWidget and sets two GeoDataPlacemarks there
3. main() calls Window::startCars()
4. Window creates two QThreads
5. Window creates two CarWorkers
6. Window moves car workers into their threads
7. Threads are started

Then each CarWorker creates QTimer with interval x. On timeout() it calls CarWorker::iterate() - function to calculate new position of placemark and notify Window (another thread) about it.

Everything is going on until application finishes.

The code with comments:

//
// This file is part of the Marble Virtual Globe.
//
// This program is free software licensed under the GNU LGPL. You can
// find a copy of this license in LICENSE.txt in the top directory of
// the source code.
//
// Copyright 2012 Illya Kovalevskyy <[email protected]>
// Copyright 2012 Torsten Rahn      <[email protected]>
//

#include <QtGui/QApplication>
#include <QtCore/QThread>
#include <QtCore/QTimer>
#include <QtCore/QHash>
#include <QtCore/qmath.h>
#include <QtCore/QDebug>
#include <QtGui/QVBoxLayout>

#include <marble/MarbleWidget.h>
#include <marble/MarbleGlobal.h>
#include <marble/GeoDataDocument.h>
#include <marble/GeoDataPlacemark.h>
#include <marble/GeoDataLineString.h>
#include <marble/GeoDataTreeModel.h>
#include <marble/MarbleModel.h>


using namespace Marble;

// CarWorker Class
class CarWorker : public QObject
{
    Q_OBJECT
public:
    CarWorker(const GeoDataCoordinates& city, qreal radius, qreal speed);

signals:
    /// This signal will be emitted when we need to
    /// move the placemark.
    void coordinatesChanged(GeoDataCoordinates coord);

public slots:
    void startWork();
    void finishWork();

private slots:
    void iterate();

private:
    QTimer *m_timer;
    GeoDataCoordinates m_city;
    qreal m_radius;
    qreal m_speed;
    qreal m_alpha;
};

CarWorker::CarWorker(const GeoDataCoordinates &city, qreal radius, qreal speed) :
    QObject(),
    m_timer(new QTimer(this)),
    m_city(city),
    m_radius(radius),
    m_speed(speed),
    m_alpha(0.0)
{}

void CarWorker::startWork()
{
    m_timer->setInterval(0);
    connect(m_timer, SIGNAL(timeout()), this, SLOT(iterate()));
    m_timer->start();
}

/// Single timer loop iteration:
/// Calculates new coordinates for the car
void CarWorker::iterate()
{
    /// A bit of math
    qreal lon = m_city.longitude(GeoDataCoordinates::Degree) + m_radius * qCos(m_alpha * DEG2RAD);
    qreal lat = m_city.latitude(GeoDataCoordinates::Degree) + m_radius * qSin(m_alpha * DEG2RAD);

    GeoDataCoordinates coord(lon, lat, 0.0, GeoDataCoordinates::Degree);
    emit coordinatesChanged(coord);

    /// Iteration is finished. We need to increase angle
    m_alpha += m_speed;
}

void CarWorker::finishWork()
{
    m_timer->stop();
}

// Window Class
class Window : public QWidget
{
    Q_OBJECT
public:
    Window(QWidget *parent = 0);
    void startCars();

public slots:
    void setCarCoordinates(const GeoDataCoordinates &coord);

private:
    MarbleWidget *m_marbleWidget;
    CarWorker *m_firstWorker;
    CarWorker *m_secondWorker;
    GeoDataPlacemark *m_carFirst;
    GeoDataPlacemark *m_carSecond;
    QThread *m_threadFirst;
    QThread *m_threadSecond;
};

Window::Window(QWidget *parent) :
    QWidget(parent),
    m_marbleWidget(new MarbleWidget)
{
    QVBoxLayout *layout = new QVBoxLayout(this);
    layout->addWidget(m_marbleWidget);
    setLayout(layout);

    // Load the OpenStreetMap map
    m_marbleWidget->setMapThemeId("earth/openstreetmap/openstreetmap.dgml");
    m_marbleWidget->setProjection( Mercator );
    setGeometry(80, 60, 1000, 800);
    GeoDataCoordinates Kiev(30.523333, 50.45, 0.0, GeoDataCoordinates::Degree);
    m_marbleWidget->centerOn(Kiev);
    m_marbleWidget->setZoom(2300);

    m_carFirst = new GeoDataPlacemark("Bus");
    m_carSecond = new GeoDataPlacemark("Car");

    GeoDataDocument *document = new GeoDataDocument;

    document->append(m_carFirst);
    document->append(m_carSecond);

    m_marbleWidget->model()->treeModel()->addDocument(document);

    show();
}

void Window::startCars()
{
    GeoDataCoordinates Kiev(30.523333, 50.45, 0.0, GeoDataCoordinates::Degree);

    m_threadFirst = new QThread;
    m_firstWorker = new CarWorker(Kiev, (qreal)0.1, (qreal)0.7);
    m_firstWorker->moveToThread(m_threadFirst);

    connect(m_firstWorker, SIGNAL(coordinatesChanged(GeoDataCoordinates)),
            this, SLOT(setCarCoordinates(GeoDataCoordinates)), Qt::BlockingQueuedConnection);

    m_threadSecond = new QThread;
    m_secondWorker = new CarWorker(Kiev, (qreal)0.2, (qreal)-0.5);
    m_secondWorker->moveToThread(m_threadSecond);

    connect(m_secondWorker, SIGNAL(coordinatesChanged(GeoDataCoordinates)),
            this, SLOT(setCarCoordinates(GeoDataCoordinates)), Qt::BlockingQueuedConnection);

    connect(m_threadFirst, SIGNAL(started()), m_firstWorker, SLOT(startWork()));
    connect(m_threadFirst, SIGNAL(finished()), m_firstWorker, SLOT(finishWork()));

    connect(m_threadSecond, SIGNAL(started()), m_secondWorker, SLOT(startWork()));
    connect(m_threadSecond, SIGNAL(finished()), m_secondWorker, SLOT(finishWork()));

    m_threadFirst->start();
    m_threadSecond->start();
}

void Window::setCarCoordinates(const GeoDataCoordinates &coord)
{
    CarWorker *worker = qobject_cast<CarWorker*>(sender());
    if (worker == m_firstWorker) {
        m_carFirst->setCoordinate(coord);
    } else if (worker == m_secondWorker) {
        m_carSecond->setCoordinate(coord);
        m_marbleWidget->model()->treeModel()->updateFeature(m_carSecond);
    }
}

// Main
int main(int argc, char** argv)
{
    QApplication app(argc,argv);

    Window window;
    window.startCars();

    return app.exec();
}

#include "vehicletracking.moc"

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