qgis二次开发

4. qgis c++二次开发 map canvas介绍

2024-06-09  本文已影响0人  雷动软件

前言

前几篇文章分别介绍了qgis二次开发的

在显示GIS数据之前，需要首先介绍一下map canvas，毕竟在将颜料(GIS地图等数据)画在画布(map canvas)之前，首先要创建画布(map canvas)。

Map canvas

QGis软件中的Map canvas

代码添加Map canvas

Map canvas is a class for displaying all GIS data types on a canvas.


image.png

Map Canvas创建和显示

void ll_qgis_base_lib::initialize(QMainWindow *mainWindow)
{
    mMainWindow = mainWindow;

    mMapCanvas = new QgsMapCanvas;
    mMapCanvas->enableAntiAliasing(true);
    mMapCanvas->setCachingEnabled(true);
    mMapCanvas->setCanvasColor(QColor(255,255,255));
    mMapCanvas->setVisible(true);

    initLayerTreeView();
    initMaptools();
}

void MainWindow::initStackwidgetPageCanvas()
{
    auto gridLayout = new QGridLayout;
    gridLayout->addWidget((QWidget*)mApp->mapCanvas());
    ui->page_canvas->setLayout(gridLayout);
    addDockWidget(Qt::LeftDockWidgetArea,mApp->layerTreeDock());
}

QGis中的QGraphicsItem

image.png

二次开发中的Item

image.png 
void MainWindow::rubberBandPolygonSlot()
{
    //添加shapefile
    QString filename = QStringLiteral("maps/shapefile/protected_areas.shp");
    QFileInfo ff(filename);
    mApp->addVectorLayer(filename,ff.baseName());
    zoomToFirstLayer<QgsVectorLayer*>();
    //定义三个点
    QgsPointXY point1(20.34013,-33.90453);
    QgsPointXY point2(20.49744,-33.91126);
    QgsPointXY point3(20.41396,-33.93079);
    //新建PolygonGeometry类型的RubberBand
    mRubberBandPolygon = new QgsRubberBand(mApp->mapCanvas(),QgsWkbTypes::PolygonGeometry);
    //添加三个点
    mRubberBandPolygon->addPoint(point1);
    mRubberBandPolygon->addPoint(point2);
    mRubberBandPolygon->addPoint(point3);
    //设置线宽颜色等属性
    mRubberBandPolygon->setWidth(4);
    mRubberBandPolygon->setColor(QColor(222,155,67));
    mRubberBandPoint = new QgsRubberBand(mApp->mapCanvas(),QgsWkbTypes::PointGeometry);
    mRubberBandPoint->addPoint(point1);
    mRubberBandPoint->addPoint(point2);
    mRubberBandPoint->addPoint(point3);
    mRubberBandPoint->setWidth(6);
    mRubberBandPoint->setColor(QColor(222,155,67));
    mRubberBandPolygon->show();
    mRubberBandPoint->show();
}

if(mVertexMarker)
    mApp->mapCanvas()->scene()->removeItem(mVertexMarker);

Layer Tree

QGis软件中的Layer Tree

image.png

代码实现layer tree

image.png 
void ll_qgis_base_lib::initLayerTreeView()
{
    //添加DockWidget作为图层树的容器
    mLayerTreeDock = new QgsDockWidget(tr("Layer Tree"));
    mLayerTreeDock->setObjectName( QStringLiteral( "Layers" ) );
    mLayerTreeDock->setAllowedAreas( Qt::LeftDockWidgetArea | Qt::RightDockWidgetArea );

    //创建Model
    QgsLayerTreeModel* model = new QgsLayerTreeModel(QgsProject::instance()->layerTreeRoot(),this);
    model->setFlag( QgsLayerTreeModel::AllowNodeReorder );
    model->setFlag( QgsLayerTreeModel::AllowNodeRename );
    model->setFlag( QgsLayerTreeModel::AllowNodeChangeVisibility );
    model->setFlag( QgsLayerTreeModel::ShowLegendAsTree );
    model->setFlag( QgsLayerTreeModel::UseEmbeddedWidgets );
    model->setFlag( QgsLayerTreeModel::UseTextFormatting );
    model->setAutoCollapseLegendNodes( 10 );

    //创建View，mLayerTreeView会在库外使用，所以需要添加getter方法，
    mLayerTreeView = new QgsLayerTreeView();
    mLayerTreeView->setModel(model);

    //Map Canvas和Layer Tree View建立联系，这样通过QgsProject::instance()->addMapLayer添加图层后，会自动添加在图层树以及会在canvas渲染图层
    mLayerTreeMapCanvasBridge = new QgsLayerTreeMapCanvasBridge(QgsProject::instance()->layerTreeRoot(),mMapCanvas,this);
    connect( mLayerTreeMapCanvasBridge, &QgsLayerTreeMapCanvasBridge::canvasLayersChanged, mMapCanvas, &QgsMapCanvas::setLayers );

    //Layer Tree View右键菜单实现
    mLayerTreeView->setMenuProvider(new ll_qgis_base_layertreeview_menu(mMainWindow,mLayerTreeView,mMapCanvas));
    connect(QgsProject::instance()->layerTreeRegistryBridge(),SIGNAL(addedLayersToLayerTree(QList<QgsMapLayer*>)),
            this,SLOT(slot_autoSelectAddedLayer(QList<QgsMapLayer*>)));
}

QgsProject(项目管理)

QGis的项目可以保存为项目文档，后缀名为“qgz”或“qgs”。在QGIS 3以前，只能通过“qgs”文件保存项目。“qgs”文件的本质是存储图层的信息等的XML文件。在QGIS 3以后，“qgz”格式采用ZIP压缩方法，不仅包含“qgs”文件，还包括附属数据库（Auxiliary Storage）文件（后缀名为“qgd”）。自QGIS 3.2以来，“qgz”文件成为QGIS项目的默认存储格式，本书也使用“qgz”文件存储QGIS项目。

QGis软件中的项目管理

代码实现

Encapsulates a QGIS project, including sets of map layers and their styles, layouts, annotations, canvases, etc.
QgsProject is available both as a singleton (QgsProject::instance()) and for use as standalone objects. The QGIS project singleton always gives access to the canonical project reference open within the main QGIS application.

void MainWindow::addShpSlot()
{
    QString filename = QStringLiteral("maps/shapefile/protected_areas.shp");
    QFileInfo ff(filename);
    //创建图层
    QgsVectorLayer* vecLayer = new QgsVectorLayer(filename,ff.baseName(),"ogr");
    if(!vecLayer->isValid())
    {
        QMessageBox::critical(this,tr("error"),tr("invalid layer"));
        return;
    }
    QgsProject::instance()->addMapLayer(vecLayer);
    zoomToFirstLayer<QgsVectorLayer*>();
}

//读取项目文件
bool    read (const QString &filename, Qgis::ProjectReadFlags flags=Qgis::ProjectReadFlags())
bool    read (Qgis::ProjectReadFlags flags=Qgis::ProjectReadFlags())
//保存项目文件
bool    write ()
bool    write (const QString &filename)

//添加单个图层
QgsMapLayer *   addMapLayer (QgsMapLayer *mapLayer, bool addToLegend=true, bool takeOwnership=true)
//添加多个图层
QList< QgsMapLayer * >  addMapLayers (const QList< QgsMapLayer * > &mapLayers, bool addToLegend=true, bool takeOwnership=true)

Q_INVOKABLE QgsMapLayer *mapLayer (const QString &layerId) const
template<class T >
T mapLayer (const QString &layerId) const
QMap< QString, QgsMapLayer * >  mapLayers (const bool validOnly=false) const
QList< QgsMapLayer * >  mapLayersByShortName (const QString &shortName) const
template<typename T >
QVector< T >    mapLayersByShortName (const QString &shortName) const

void    removeAllMapLayers ()
void    removeMapLayer (const QString &layerId)
void    removeMapLayer (QgsMapLayer *layer)
void    removeMapLayers (const QList< QgsMapLayer * > &layers)
void    removeMapLayers (const QStringList &layerIds)

总结

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