OSM Buildings

A 3D building viewer of OSM (OpenStreetMap) buildings map data.

Overview

This application demonstrates how to create 3D building geometry for display on a map using data from OpenStreetMap (OSM) servers or a locally limited data set when the server is unavailable.

Queue handling

The application uses a queue to handle concurrent requests to boost up the loading process of maps and building data.

OSMRequest::OSMRequest(QObject *parent)
    : QObject{parent}
{
    connect( &m_queuesTimer, &QTimer::timeout, this, [this](){
        if ( m_buildingsQueue.isEmpty() && m_mapsQueue.isEmpty() ) {
            m_queuesTimer.stop();
        }
        else {

#ifdef QT_DEBUG
            const int numConcurrentRequests = 1;
#else
            const int numConcurrentRequests = 6;
#endif
            if ( !m_buildingsQueue.isEmpty() && m_buildingsNumberOfRequestsInFlight < numConcurrentRequests ) {
                getBuildingsDataRequest(m_buildingsQueue.dequeue());
                ++m_buildingsNumberOfRequestsInFlight;
            }

            if ( !m_mapsQueue.isEmpty() && m_mapsNumberOfRequestsInFlight < numConcurrentRequests ) {
                getMapsDataRequest(m_mapsQueue.dequeue());
                ++m_mapsNumberOfRequestsInFlight;
            }
        }
    });
    m_queuesTimer.setInterval(0);

Fetching and parsing data

A custom request handler class is implemented for fetching the data from the OSM building and map servers.

void OSMRequest::getBuildingsData(const QQueue<OSMTileData> &buildingsQueue) {

    if ( buildingsQueue.isEmpty() )
        return;
    m_buildingsQueue = buildingsQueue;
    if ( !m_queuesTimer.isActive() )
        m_queuesTimer.start();
}

void OSMRequest::getBuildingsDataRequest(const OSMTileData &tile)
{
    const QString fileName = "data/"_L1 + tileKey(tile) + ".json"_L1;
    QFileInfo file(fileName);
    if ( file.size() > 0 ) {
        QFile file(fileName);
        if (file.open(QFile::ReadOnly)){
            QByteArray data = file.readAll();
            file.close();
            emit buildingsDataReady( importGeoJson(QJsonDocument::fromJson( data )), tile.TileX, tile.TileY, tile.ZoomLevel );
            --m_buildingsNumberOfRequestsInFlight;
            return;
        }
    }

    QUrl url = QUrl(QString(URL_OSMB_JSON).arg(QString::number(tile.ZoomLevel),
                                               QString::number(tile.TileX),
                                               QString::number(tile.TileY),
                                               m_token));
    QNetworkReply * reply = m_networkAccessManager.get( QNetworkRequest(url));
    connect( reply, &QNetworkReply::finished, this, [this, reply, tile](){
        reply->deleteLater();
        if ( reply->error() == QNetworkReply::NoError ) {
            QByteArray data = reply->readAll();
            emit buildingsDataReady( importGeoJson(QJsonDocument::fromJson( data )), tile.TileX, tile.TileY, tile.ZoomLevel );
        } else {
            const QByteArray message = reply->readAll();
            static QByteArray lastMessage;
            if (message != lastMessage) {
                lastMessage = message;
                qWarning().noquote() << "OSMRequest::getBuildingsData " << reply->error()
                                     << reply->url() << message;
            }
        }
        --m_buildingsNumberOfRequestsInFlight;
    } );
void OSMRequest::getMapsData(const QQueue<OSMTileData> &mapsQueue) {

    if ( mapsQueue.isEmpty() )
        return;
    m_mapsQueue = mapsQueue;
    if ( !m_queuesTimer.isActive() )
        m_queuesTimer.start();
}

void OSMRequest::getMapsDataRequest(const OSMTileData &tile)
{
    const QString fileName = "data/"_L1 + tileKey(tile) + ".png"_L1;
    QFileInfo file(fileName);
    if ( file.size() > 0) {
        QFile file(fileName);
        if (file.open(QFile::ReadOnly)){
            QByteArray data = file.readAll();
            file.close();
            emit mapsDataReady(  data, tile.TileX, tile.TileY, tile.ZoomLevel );
            --m_mapsNumberOfRequestsInFlight;
            return;
        }
    }

    QUrl url = QUrl(QString(URL_OSMB_MAP).arg(QString::number(tile.ZoomLevel),
                                              QString::number(tile.TileX),
                                              QString::number(tile.TileY)));
    QNetworkReply * reply = m_networkAccessManager.get( QNetworkRequest(url));
    connect( reply, &QNetworkReply::finished, this, [this, reply, tile](){
        reply->deleteLater();
        if ( reply->error() == QNetworkReply::NoError ) {
            QByteArray data = reply->readAll();
            emit mapsDataReady( data, tile.TileX, tile.TileY, tile.ZoomLevel );
        } else {
            const QByteArray message = reply->readAll();
            static QByteArray lastMessage;
            if (message != lastMessage) {
                lastMessage = message;
                qWarning().noquote() << "OSMRequest::getMapsDataRequest" << reply->error()
                                     << reply->url() << message;
            }
        }
        --m_mapsNumberOfRequestsInFlight;
    } );

The application parses the online data to convert it to a QVariant list of keys and values in geo formats such as QGeoPolygon.

            emit buildingsDataReady( importGeoJson(QJsonDocument::fromJson( data )), tile.TileX, tile.TileY, tile.ZoomLevel );
            --m_buildingsNumberOfRequestsInFlight;

The parsed building data is sent to a custom geometry item to convert the geo coordinates to 3D coordinates.

    constexpr auto convertGeoCoordToVertexPosition = [](const float lat, const float lon) -> QVector3D {

        const double scale = 1.212;
        const double geoToPositionScale = 1000000 * scale;
        const double XOffsetFromCenter = 537277 * scale;
        const double YOffsetFromCenter = 327957 * scale;
        double x = (lon/360.0 + 0.5) * geoToPositionScale;
        double y = (1.0-log(qTan(qDegreesToRadians(lat)) + 1.0 / qCos(qDegreesToRadians(lat))) / M_PI) * 0.5 * geoToPositionScale;
        return QVector3D( x - XOffsetFromCenter, YOffsetFromCenter - y, 0.0 );
    };

The required data for the index and vertex buffers, such as position, normals, tangents, and UV coordinates, is generated.

    for ( const QVariant &baseData : geoVariantsList ) {
        for ( const QVariant &dataValue : baseData.toMap()["data"_L1].toList() ) {
            const auto featureMap = dataValue.toMap();
            const auto properties = featureMap["properties"_L1].toMap();
            const auto buildingCoords = featureMap["data"_L1].value<QGeoPolygon>().perimeter();
            float height = 0.15 * properties["height"_L1].toLongLong();
            float levels = static_cast<float>(properties["levels"_L1].toLongLong());
            QColor color = QColor::fromString( properties["color"_L1].toString());
            if ( !color.isValid() || color == QColor(Qt::GlobalColor::black))
                color = QColor(Qt::GlobalColor::white);
            QColor roofColor = QColor::fromString( properties["roofColor"_L1].toString());
            if ( !roofColor.isValid() || roofColor == QColor(Qt::GlobalColor::black) )
                roofColor = color;

            QVector3D subsetMinBound = QVector3D(maxFloat, maxFloat, maxFloat);
            QVector3D subsetMaxBound = QVector3D(minFloat, minFloat, minFloat);

            qsizetype numSubsetVertices = buildingCoords.size() * 2;
            qsizetype lastVertexDataCount = vertexData.size();
            qsizetype lastIndexDataCount = indexData.size();
            vertexData.resize( lastVertexDataCount + numSubsetVertices * strideVertex );
            indexData.resize( lastIndexDataCount + ( numSubsetVertices - 2 ) * stridePrimitive );

            float *vbPtr = &reinterpret_cast<float *>(vertexData.data())[globalVertexCounter * strideVertexLen];
            uint32_t *ibPtr = &reinterpret_cast<uint32_t *>(indexData.data())[globalPrimitiveCounter * 3];

            qsizetype subsetVertexCounter = 0;

            QVector3D lastBaseVertexPos;
            QVector3D lastExtrudedVertexPos;
            QVector3D currentBaseVertexPos;
            QVector3D currentExtrudedVertexPos;
            QVector3D subsetPolygonCenter;

            using PolygonVertex = std::array<double, 2>;
            using PolygonVertices = std::vector<PolygonVertex>;

            PolygonVertices roofPolygonVertices;

            for ( const QGeoCoordinate &buildingPoint : buildingCoords ) {
   ...
                    std::vector<PolygonVertices> roofPolygonsVertices;
                    roofPolygonsVertices.push_back( roofPolygonVertices );
                    std::vector<uint32_t> roofIndices = mapbox::earcut<uint32_t>(roofPolygonsVertices);

                    lastVertexDataCount = vertexData.size();
                    lastIndexDataCount = indexData.size();
                    vertexData.resize( lastVertexDataCount + roofPolygonVertices.size() * strideVertex );
                    indexData.resize( lastIndexDataCount + roofIndices.size() * sizeof(uint32_t) );

                    vbPtr = &reinterpret_cast<float *>(vertexData.data())[globalVertexCounter * strideVertexLen];
                    ibPtr = &reinterpret_cast<uint32_t *>(indexData.data())[globalPrimitiveCounter * 3];

                    for ( const uint32_t &roofIndex : roofIndices ) {
                        *ibPtr++ = roofIndex + globalVertexCounter;
                    }
                    qsizetype roofPrimitiveCount = roofIndices.size() / 3;
                    globalPrimitiveCounter += roofPrimitiveCount;

                    for ( const PolygonVertex &polygonVertex : roofPolygonVertices ) {

                        //position
                        *vbPtr++ = polygonVertex.at(0);
                        *vbPtr++ = polygonVertex.at(1);
                        *vbPtr++ = height;

                        //normal
                        *vbPtr++ = 0.0;
                        *vbPtr++ = 0.0;
                        *vbPtr++ = 1.0;

                        //tangent
                        *vbPtr++ = 1.0;
                        *vbPtr++ = 0.0;
                        *vbPtr++ = 0.0;

                        //binormal
                        *vbPtr++ = 0.0;
                        *vbPtr++ = 1.0;
                        *vbPtr++ = 0.0;

                        //color/
                        *vbPtr++ = roofColor.redF();
                        *vbPtr++ = roofColor.greenF();
                        *vbPtr++ = roofColor.blueF();
                        *vbPtr++ = 1.0;

                        //texcoord
                        *vbPtr++ = 1.0;
                        *vbPtr++ = 1.0;

                        *vbPtr++ = 0.0;
                        *vbPtr++ = 1.0;

                        ++subsetVertexCounter;
                        ++globalVertexCounter;
                    }

                }

            }
        }
    }

    clear();

The downloaded PNG data is sent to a custom QQuick3DTextureData item to convert the PNG format to a texture for map tiles.

void CustomTextureData::setImageData(const QByteArray &data)
{
    QImage image = QImage::fromData(data).convertToFormat(QImage::Format_RGBA8888);
    setTextureData( QByteArray(reinterpret_cast<const char*>(image.constBits()), image.sizeInBytes()) );
    setSize( image.size() );
    setHasTransparency(false);
    setFormat(Format::RGBA8);
}

The application uses camera position, orientation, zoom level, and tilt to find the nearest tiles in the view.

void OSMManager::setCameraProperties(const QVector3D &position, const QVector3D &right,
                                    float cameraZoom, float minimumZoom, float maximumZoom,
                                    float cameraTilt, float minimumTilt, float maximumTilt)
{

    float tiltFactor = (cameraTilt - minimumTilt) / qMax(maximumTilt - minimumTilt, 1.0);
    float zoomFactor = (cameraZoom - minimumZoom) / qMax(maximumZoom - minimumZoom, 1.0);

    // Forward vector align to the XY plane
    QVector3D forwardVector = QVector3D::crossProduct(right,
                                                      QVector3D(0.0, 0.0, -1.0)).normalized();
    QVector3D projectionOfForwardOnXY = position
            + forwardVector * tiltFactor * zoomFactor * 50.0;

    QQueue<OSMTileData> queue;
    for ( int forwardIndex = -20; forwardIndex <= 20; ++forwardIndex ){
        for ( int sidewardIndex = -20; sidewardIndex <= 20; ++sidewardIndex ){
            QVector3D transferredPosition = projectionOfForwardOnXY
                      + QVector3D(float(m_tileSizeX * sidewardIndex), float(m_tileSizeY * forwardIndex), 0.0);
            addBuildingRequestToQueue(queue, m_startBuildingTileX + int(transferredPosition.x() / m_tileSizeX),
                                m_startBuildingTileY - int(transferredPosition.y() / m_tileSizeY));
        }
    }

    const QPoint projectedTile{m_startBuildingTileX + int(projectionOfForwardOnXY.x() / m_tileSizeX),
                               m_startBuildingTileY - int(projectionOfForwardOnXY.y() / m_tileSizeY)};

    auto closer = [projectedTile](const OSMTileData &v1, const OSMTileData &v2) -> bool {
        return v1.distanceTo(projectedTile) < v2.distanceTo(projectedTile);
    };
    std::sort(queue.begin(), queue.end(), closer);

    m_request->getBuildingsData( queue );
    m_request->getMapsData( queue );

Generates the tiles request queue.

void OSMManager::addBuildingRequestToQueue(QQueue<OSMTileData> &queue, int tileX, int tileY, int zoomLevel)
{
    OSMTileData data{tileX, tileY, zoomLevel};

Controls

When you run the application, use the following controls for navigation.

	Windows	Android
Pan	Left mouse button + drag	Drag
Zoom	Mouse wheel	Pinch
Rotate	Right mouse button + drag	n/a

        OSMCameraController {
            id: cameraController
            origin: originNode
            camera: cameraNode
        }

Rendering

Every chunk of the map tile consists of a QML model (the 3D geometry) and a custom material which uses a rectangle as a base to render the tilemap texture.

        ...
        id: chunkModelMap
        Node {
            property variant mapData: null
            property int tileX: 0
            property int tileY: 0
            property int zoomLevel: 0
            Model {
                id: basePlane
                position: Qt.vector3d( osmManager.tileSizeX * tileX, osmManager.tileSizeY * -tileY, 0.0 )
                scale: Qt.vector3d( osmManager.tileSizeX / 100., osmManager.tileSizeY / 100., 0.5)
                source: "#Rectangle"
                materials: [
                    CustomMaterial {
                        property TextureInput tileTexture: TextureInput {
                            enabled: true
                            texture: Texture {
                                textureData: CustomTextureData {
                                    Component.onCompleted: setImageData( mapData )
                                } }
                        }
                        shadingMode: CustomMaterial.Shaded
                        cullMode: Material.BackFaceCulling
                        fragmentShader: "customshadertiles.frag"
                    }
                ]
            }

The application uses custom geometry to render tile buildings.

        ...
        id: chunkModelBuilding
        Node {
            property variant geoVariantsList: null
            property int tileX: 0
            property int tileY: 0
            property int zoomLevel: 0
            Model {
                id: model
                scale: Qt.vector3d(1, 1, 1)

                OSMGeometry {
                    id: osmGeometry
                    Component.onCompleted: updateData( geoVariantsList )
                    onGeometryReady:{
                        model.geometry = osmGeometry
                    }
                }
                materials: [

                    CustomMaterial {
                        shadingMode: CustomMaterial.Shaded
                        cullMode: Material.BackFaceCulling
                        vertexShader: "customshaderbuildings.vert"
                        fragmentShader: "customshaderbuildings.frag"
                    }
                ]
            }

To render building parts such as rooftops with one draw call, a custom shader is used.

// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause

VARYING vec4 color;

float rectangle(vec2 samplePosition, vec2 halfSize) {
    vec2 componentWiseEdgeDistance = abs(samplePosition) - halfSize;
    float outsideDistance = length(max(componentWiseEdgeDistance, 0.0));
    float insideDistance = min(max(componentWiseEdgeDistance.x, componentWiseEdgeDistance.y), 0.0);
    return outsideDistance + insideDistance;
}

void MAIN() {
    vec2 tc = UV0;
    vec2 uv = fract(tc * UV1.x); //UV1.x number of levels
    uv = uv * 2.0 - 1.0;
    uv.x = 0.0;
    uv.y = smoothstep(0.0, 0.2, rectangle( vec2(uv.x, uv.y + 0.5), vec2(0.2)) );
    BASE_COLOR = vec4(color.xyz * mix( clamp( ( vec3( 0.4, 0.4, 0.4 ) + tc.y)
                                             * ( vec3( 0.6, 0.6, 0.6 ) + uv.y)
                                             , 0.0, 1.0), vec3(1.0), UV1.y ), 1.0); // UV1.y as is roofTop
    ROUGHNESS = 0.3;
    METALNESS = 0.0;
    FRESNEL_POWER = 1.0;
}

Running the Example

To run the example from Qt Creator, open the Welcome mode and select the example from Examples. For more information, see Qt Creator: Tutorial: Build and run.

Example project @ code.qt.io

See also QML Applications.

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