Offline Mapping

[JonB]

@suslucoder
They are defining that string but never using it? You could always have told us in which file in the example code...

[deleted286]

@JonB on slippymap.cpp

#include <QtWidgets>
#include <QtNetwork>
#include "slippymap.h"
#include "qmath.h"

uint qHash(const QPoint& p)
{
    return p.x() * 17 ^ p.y();
}

// tile size in pixels
const int tdim = 256;

QPointF tileForCoordinate(qreal lat, qreal lng, int zoom)
{
    qreal radianLat = qDegreesToRadians(lat);
    qreal zn = static_cast<qreal>(1 << zoom);
    qreal tx = (lng + 180.0) / 360.0;
    qreal ty = 0.5 - log(tan(radianLat) + 1.0 / cos(radianLat)) / M_PI / 2.0;
    return QPointF(tx * zn, ty * zn);
}

qreal longitudeFromTile(qreal tx, int zoom)
{
    qreal zn = static_cast<qreal>(1 << zoom);
    qreal lat = tx / zn * 360.0 - 180.0;
    return lat;
}

qreal latitudeFromTile(qreal ty, int zoom)
{
    qreal zn = static_cast<qreal>(1 << zoom);
    qreal n = M_PI - 2 * M_PI * ty / zn;
    return qRadiansToDegrees(atan(sinh(n)));
}


SlippyMap::SlippyMap(QObject *parent)
    : QObject(parent), width(400), height(300), zoom(15),
      latitude(59.9138204), longitude(10.7387413)
{
    m_emptyTile = QPixmap(tdim, tdim);
    m_emptyTile.fill(Qt::lightGray);

    QNetworkDiskCache *cache = new QNetworkDiskCache;
    cache->setCacheDirectory(QStandardPaths::writableLocation(QStandardPaths::CacheLocation));
    m_manager.setCache(cache);
    connect(&m_manager, SIGNAL(finished(QNetworkReply*)),
            this, SLOT(handleNetworkData(QNetworkReply*)));
}

void SlippyMap::invalidate()
{
    if (width <= 0 || height <= 0)
        return;

    QPointF ct = tileForCoordinate(latitude, longitude, zoom);
    qreal tx = ct.x();
    qreal ty = ct.y();

    // top-left corner of the center tile
    int xp = width / 2 - (tx - floor(tx)) * tdim;
    int yp = height / 2 - (ty - floor(ty)) * tdim;

    // first tile vertical and horizontal
    int xa = (xp + tdim - 1) / tdim;
    int ya = (yp + tdim - 1) / tdim;
    int xs = static_cast<int>(tx) - xa;
    int ys = static_cast<int>(ty) - ya;

    // offset for top-left tile
    m_offset = QPoint(xp - xa * tdim, yp - ya * tdim);

    // last tile vertical and horizontal
    int xe = static_cast<int>(tx) + (width - xp - 1) / tdim;
    int ye = static_cast<int>(ty) + (height - yp - 1) / tdim;

    // build a rect
    m_tilesRect = QRect(xs, ys, xe - xs + 1, ye - ys + 1);

    if (m_url.isEmpty())
        download();

    emit updated(QRect(0, 0, width, height));
}

void SlippyMap::render(QPainter *p, const QRect &rect)
{
    for (int x = 0; x <= m_tilesRect.width(); ++x)
        for (int y = 0; y <= m_tilesRect.height(); ++y) {
            QPoint tp(x + m_tilesRect.left(), y + m_tilesRect.top());
            QRect box = tileRect(tp);
            if (rect.intersects(box)) {
                if (m_tilePixmaps.contains(tp))
                    p->drawPixmap(box, m_tilePixmaps.value(tp));
                else
                    p->drawPixmap(box, m_emptyTile);
            }
        }
}

void SlippyMap::pan(const QPoint &delta)
{
    QPointF dx = QPointF(delta) / qreal(tdim);
    QPointF center = tileForCoordinate(latitude, longitude, zoom) - dx;
    latitude = latitudeFromTile(center.y(), zoom);
    longitude = longitudeFromTile(center.x(), zoom);
    invalidate();
}

void SlippyMap::handleNetworkData(QNetworkReply *reply)
{
    QImage img;
    QPoint tp = reply->request().attribute(QNetworkRequest::User).toPoint();
    if (!reply->error())
        if (!img.load(reply, 0))
            img = QImage();
    reply->deleteLater();
    m_tilePixmaps[tp] = QPixmap::fromImage(img);
    if (img.isNull())
        m_tilePixmaps[tp] = m_emptyTile;
    emit updated(tileRect(tp));

    // purge unused spaces
    const QRect bound = m_tilesRect.adjusted(-2, -2, 2, 2);
    for (auto it = m_tilePixmaps.keyBegin(); it != m_tilePixmaps.keyEnd(); ++it) {
        const QPoint &tp = *it;
        if (!bound.contains(tp))
            m_tilePixmaps.remove(tp);
    }

    download();
}

void SlippyMap::download()
{
    QPoint grab(0, 0);
    for (int x = 0; x <= m_tilesRect.width(); ++x)
        for (int y = 0; y <= m_tilesRect.height(); ++y) {
            QPoint tp = m_tilesRect.topLeft() + QPoint(x, y);
            if (!m_tilePixmaps.contains(tp)) {
                grab = tp;
                break;
            }
        }
    if (grab == QPoint(0, 0)) {
        m_url = QUrl();
        return;
    }

    QString path = "http://tile.openstreetmap.org/%1/%2/%3.png";
    m_url = QUrl(path.arg(zoom).arg(grab.x()).arg(grab.y()));
    QNetworkRequest request;
    request.setUrl(m_url);
    request.setRawHeader("User-Agent", "The Qt Company (Qt) Graphics Dojo 1.0");
    request.setAttribute(QNetworkRequest::User, QVariant(grab));
    m_manager.get(request);
}

QRect SlippyMap::tileRect(const QPoint &tp)
{
    QPoint t = tp - m_tilesRect.topLeft();
    int x = t.x() * tdim + m_offset.x();
    int y = t.y() * tdim + m_offset.y();
    return QRect(x, y, tdim, tdim);
}

[JonB]

@suslucoder
So why do you say it does not use it, or it's doing something else??

    QString path = "http://tile.openstreetmap.org/%1/%2/%3.png";
    m_url = QUrl(path.arg(zoom).arg(grab.x()).arg(grab.y()));

It's using it on the following line!

[deleted286]

@JonB you are so clear!
I wouldn't ask such a question if I understood what they were doing

[JonB]

@suslucoder
OK, forget the QUrl part on that second line. path is a QString. And it's using path.arg().arg().... Look up exactly what @jsulm referred you to:

I post the link once more: https://doc.qt.io/qt-5/qstring.html#arg

That explains exactly why there are %1, %2s etc. in the string and what QString::arg() does with them. He & I don't know how to explain any better!

[jsulm]

@suslucoder Maybe one example:

QString path = "http://tile.openstreetmap.org/%1/%2/%3.png";
qDebug() << path.arg("ONE").arg("TWO").arg("THREE");

Will output: http://tile.openstreetmap.org/ONE/TWO/THREE.png

[deleted286]

@jsulm understand now. Thank you

[deleted286]

@jsulm I understand it. You locked my question, but it was another question.
Im trying to find a way for tile a map.

[jsulm]

@suslucoder said in Offline Mapping:

You locked my question

Which one?

[Christian Ehrlicher]

@jsulm said in Offline Mapping:

Which one?

It was me. The question was to similar.