Marble/Runners/VehicleTracking

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Tutorial Series   Marble C++ Tutorial
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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. Imagine that there are two flying cars in the air. 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


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 a nice implementation plan. Let's start coding.

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

Everything is going on until the 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]>
//

#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:
    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();
}

void CarWorker::iterate()
{
    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);

    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);
        m_marbleWidget->model()->treeModel()->updateFeature(m_carFirst);
    } else if (worker == m_secondWorker) {
        m_carSecond->setCoordinate(coord);
        m_marbleWidget->model()->treeModel()->updateFeature(m_carSecond);
    }
}

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

    Window window;
    window.startCars();

    return app.exec();
}

#include "vehicletracking.moc"

Before running qmake, create a qmake project file 

TEMPLATE = app
TARGET = vehicletracking
DEPENDPATH += .
INCLUDEPATH += .
SOURCES += vehicletracking.cpp
LIBS += -lmarblewidget

Save this file as "vehicletracking.pro" in the same directory and run 

qmake
make

then execute ./vehicletracking. If everything goes fine, marble widget will appear as shown in the screenshot at the start of the tutorial.

Find your way and explore the world! ;)

The latest source code of this example can be found at vehicletracking.cpp and vehicletracking.h.

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