how to display locations from a file in QML - c++

Question

I want to display a huge number of points on a map with Qt/QML. These points are detailled in a .txt file.
I'm looking for the process to use but, unfortunately, I only find a query method via a plugin to display places from a server (osm, google...). I can't use it, these points being very specific.
What is the best way to achieve this task ?
Also, is it necessary to use "plugin itemsoverlay" in addition to the "osm plugin" to show these points on a specific layer ?
Thanks for help.
Ok, back to fight with code now.
Here is the main .cpp
#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QQmlContext>
#include <QObject>
#include <QGeoCoordinate>
#include <QDebug>
class NavaidsPoint: public QObject
{
Q_OBJECT
Q_PROPERTY(QGeoCoordinate position READ position WRITE setPosition NOTIFY positionChanged)
public:
NavaidsPoint(QString code, double latitude, double longitude, QString country = "")
{
m_code = code;
m_latitude = latitude;
m_longitude = longitude;
m_country = country;
m_position.setLatitude(latitude);
m_position.setLongitude(longitude);
}
void setPosition(const QGeoCoordinate &c) { //Affectation des nouvelles coordonnées de position
if (m_position == c)
return;
m_position = c;
emit positionChanged(); //Emission du signal de changement de position
}
QGeoCoordinate position() const
{
return m_position; //Lecture des coordonnées de position
}
Q_INVOKABLE QString oaciCode() const {
return m_code;
}
Q_INVOKABLE QString countryCode() const {
return m_country;
}
signals:
void positionChanged();
private:
QGeoCoordinate m_position;
double m_latitude;
double m_longitude;
double m_altitude;
QString m_code;
QString m_country;
};
int main(int argc, char *argv[])
{
QGuiApplication app(argc, argv);
NavaidsPoint oslo("Oslo", 59.9154, 10.7425, "NG");
QQmlApplicationEngine engine;
engine.rootContext()->setContextProperty("oslo", &oslo);
engine.load(QUrl(QStringLiteral("qrc:/main.qml")));
if (engine.rootObjects().isEmpty())
return -1;
return app.exec();
}
#include "main.moc"
And the main.qml
import QtQuick 2.6
import QtQuick.Window 2.2
import QtPositioning 5.5
import QtLocation 5.6
Window {
width: 700
height: 500
visible: true
title: qsTr("Test implantation coordonnées")
property variant topLeftEurope: QtPositioning.coordinate(60.5, 0.0)
property variant bottomRightEurope: QtPositioning.coordinate(51.0, 14.0)
property variant viewOfEurope:
QtPositioning.rectangle(topLeftEurope, bottomRightEurope)
Map {
id: mapOfEurope
anchors.centerIn: parent;
anchors.fill: parent
plugin: Plugin {
name: "osm"
}
MapCircle {
center: oslo.position
radius: 5000.0
color: 'green'
border.width: 3
MouseArea {
anchors.fill: parent
onDoubleClicked: {
console.log("Doubleclick on " + oslo.oaciCode())
}
onClicked: {
console.log("Point : " + oslo.oaciCode() + " " + oslo.position + " " + oslo.countryCode())
}
}
}
visibleRegion: viewOfEurope
}
}
everything works fine with this unique point Oslo. Now I need to place thousands of points. This structure cannot work like that, because I need to implement one NavaidsPoint for each of them and setContextProperty for each of them again. Likewise, in the main.QML the circle is tied with the object :
center : oslo.position
and in addition, I nead the oaciCode and the countryCode. So this part of the code must be generic, not specific to a single object.
So, what could be the best way to solve this problem ?
I hope to be in the SO scope with these precisions.
Thanks again for help.

Answer 1

If you want to load many elements a good option is to use MapItemView, this requires a model that provides the data, and indicate the appropriate delegate.
The model is created based on a QAbstractListModel where we will use the roles to expose the properties to QML, for it creates a class that does not necessarily have to inherit from QObject, in this case it will be the following.
#ifndef NAVAIDSPOINT_H
#define NAVAIDSPOINT_H
#include <QGeoCoordinate>
#include <QString>
class NavaidsPoint
{
public:
NavaidsPoint(QString code, double latitude, double longitude, QString country = ""){
m_code = code;
m_country = country;
m_position.setLatitude(latitude);
m_position.setLongitude(longitude);
m_position.setAltitude(0.0);
}
void setPosition(const QGeoCoordinate &c) { //Affectation des nouvelles coordonnées de position
m_position = c;
}
QGeoCoordinate position() const{
return m_position; //Lecture des coordonnées de position
}
QString oaciCode() const {
return m_code;
}
QString countryCode() const {
return m_country;
}
private:
QGeoCoordinate m_position;
QString m_code;
QString m_country;
};
#endif // NAVAIDSPOINT_H
QAbstractListModel requires that you implement the methods rowCount, data and roleNames, also I have implemented the add method where you must notify the model of the changes, an example is as follow
#ifndef NAVAIDSMODEL_H
#define NAVAIDSMODEL_H
#include "navaidspoint.h"
#include <QAbstractListModel>
#include <QFile>
#include <QTextStream>
#include <QDebug>
class NavaidsModel : public QAbstractListModel
{
Q_OBJECT
public:
NavaidsModel(QObject *parent = Q_NULLPTR):QAbstractListModel(parent){
}
enum NavaidsRoles {
PositionRole = Qt::UserRole + 1,
OACICodeRole,
CountryCodeRole
};
void readFromCSV(const QString &filename){
QFile file(filename);
if(!file.open(QFile::ReadOnly | QFile::Text))
return;
QTextStream in(&file);
while (!in.atEnd()) {
QString line = in.readLine();
QStringList elements = line.split(",");
if(elements.count()==4){
QString code = elements[0];
double latitude = elements[1].toDouble();
double longitude = elements[2].toDouble();
QString country = elements[3];
NavaidsPoint p(code, latitude, longitude, country);
addNavaidsPoint(p);
}
}
}
void addNavaidsPoint(const NavaidsPoint &point){
beginInsertRows(QModelIndex(), rowCount(), rowCount());
mPoints << point;
endInsertRows();
}
int rowCount(const QModelIndex & parent = QModelIndex()) const{
Q_UNUSED(parent)
return mPoints.count();
}
QVariant data(const QModelIndex & index, int role=Qt::DisplayRole) const {
if (index.row() < 0 || index.row() >= mPoints.count())
return QVariant();
const NavaidsPoint &point = mPoints[index.row()];
if (role == PositionRole)
return QVariant::fromValue(point.position());
else if (role == OACICodeRole)
return point.oaciCode();
else if (role == CountryCodeRole)
return point.countryCode();
return QVariant();
}
protected:
QHash<int, QByteArray> roleNames() const {
QHash<int, QByteArray> roles;
roles[PositionRole] = "position";
roles[OACICodeRole] = "oaci";
roles[CountryCodeRole] = "country";
return roles;
}
private:
QList<NavaidsPoint> mPoints;
};
#endif // NAVAIDSMODEL_H
After the model is created, the models are added and we expose it to QML:
#include "navaidsmodel.h"
#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QQmlContext>
int main(int argc, char *argv[])
{
QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
QGuiApplication app(argc, argv);
NavaidsModel model;
model.readFromCSV("/home/eyllanesc/data.csv"); //from file
model.addNavaidsPoint(NavaidsPoint("Oslo", 59.9154, 10.7425, "NG")); // add new point
QQmlApplicationEngine engine;
engine.rootContext()->setContextProperty("navaidsModel", &model);
engine.load(QUrl(QLatin1String("qrc:/main.qml")));
if (engine.rootObjects().isEmpty())
return -1;
return app.exec();
}
and at the end, MapItemView is used with the appropriate model and delegate:
import QtQuick 2.6
import QtQuick.Window 2.2
import QtPositioning 5.5
import QtLocation 5.6
Window {
width: 700
height: 500
visible: true
title: qsTr("Test implantation coordonnées")
property variant topLeftEurope: QtPositioning.coordinate(60.5, 0.0)
property variant bottomRightEurope: QtPositioning.coordinate(51.0, 14.0)
property variant viewOfEurope:
QtPositioning.rectangle(topLeftEurope, bottomRightEurope)
Map {
id: mapOfEurope
anchors.centerIn: parent;
anchors.fill: parent
plugin: Plugin {
name: "osm"
}
MapItemView {
model: navaidsModel
delegate: MapCircle{
center: position
radius: 10000
color: 'green'
border.width: 3
MouseArea {
anchors.fill: parent
onDoubleClicked: {
console.log("Doubleclick on " + oaci)
}
onClicked: {
console.log("Point : " + oaci + " " + position + " " + country)
}
}
}
}
visibleRegion: viewOfEurope
}
}
In the following link is the complete example.