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.
See also QML Applications.