創建畫布（QgsMapCanvas）
QgsMapCanvas * canvas = new QgsMapCanvas; canvas->setCanvasColor(Qt::white); //設置畫布顏色 canvas->enableAntiAliasing(true); //啟用抗鋸齒 canvas->setExtent(vlayer->extent()); //設置圖層范圍 vlayer矢量圖層 canvas->setLayers(vLayer); //設置圖層集合 canvas->setVisible(true); //設置是否可見 canvas->freeze(false); //設置是否凍結對圖層的操作 canvas->refresh(); //刷新 canvas->show(); //顯示
創建圖層（QgsMapLayer）
//幾何類型,"Point", "LineString", "Polygon", "MultiPoint", "MultiLineString", "MultiPolygon" QString path = "multiPoint"
path.append( QString( "crs=EPSG:4326&")); //參照坐標系 path.append( QString( "field=id:integer&field=name:string(50)&")); //添加字段屬性 path.append( QString( "index=yes&" )); //創建索引 path.append( QString( "memoryid=%1").arg(QUuid::createUuid().toString())); //臨時編碼 //創建矢量圖層 QgsVectorLayer *vLayer = new QgsVectorLayer(path, "MyPoint", "memory");
在圖層插入點要素（QgsFeature）
//創建一個點圖層 QgsVectorLayer* pointLayer = new QgsVectorLayer("Point?crs=epsg:4326", "MyPoint", "memory"); QgsVectorDataProvider* dataProvider = pointLayer->dataProvider(); //創建一個要素 QgsFeature MyFeature; //設置在地圖的插入點的坐標 MyFeature.setGeometry( QgsGeometry::fromPointXY( QgsPointXY(116.3215, 39.5416) ) ); dataProvider->addFeatures(QgsFeatureList()<<MyFeature);
pointLayer->updateExtents();
//pointLayer->setCoordinateSystem();
在圖層插入線要素（QgsFeature）
//創建一個線圖層 QgsVectorLayer *lineLayer = new QgsVectorLayer("LineString?crs=epsg:4326", "MyLine", "memory"); QgsVectorDataProvider* dataProder = lineLayer->dataProvider(); //在指定坐標添加點 QgsFeature feature; QgsGeometry geometry = QgsGeometry::fromPointXY( QgsPointXY(50,50) ); //通過點坐標進行畫線 QgsPolyline line ; line << QgsPoint(100.4443, 32.2123) << QgsPoint(130.5557, 50.4445); geometry = QgsGeometry::fromPolyline(line); feature.setGeometry(geometry); dataProder->addFeatures(QgsFeatureList()<<feature); lineLayer->updateExtents();
//lineLayer->setCoordinateSystem();
在圖層添加字段，並對指定要素設置屬性（QgsField）
//創建圖層 QgsVectorLayer alarmLayer = new QgsVectorLayer("Point?crs=epsg:4326", "alarmLayer", "memory"); //添加字段 alarmLayer->startEditing(); QgsField* filed = new QgsField(QStringLiteral("頻率"), QVariant::String); alarmLayer->addAttribute(*filed)); //也可通過alarmLayer->dataProvier()->addAttributes(QgsFields); alarmLayer->updateFields(); alarmLayer->commitChanges(); //根據id添加屬性 alarmLayer->startEditing(); alarmLayer->changeAttributeValue(id, field, attribute); alarmLayer->commitChanges();
在圖層中刪除要素
QgsVectorLayer planeLayer = new QgsVectorLayer("Point?crs=epsg:4326", "MyPoint", "memory"); //啟用編輯 planeLayer->startEditing(); planeLayer->deleteFeature( QgsFeatureId(對應id) ); planeLayer->updateExtents(); //提交修改 planeLayer->commitChanges();
設置點樣式（點圖層渲染 QgsFeatureRenderer）
My_MapCanvas->freeze(); //獲取SVG矢量圖標，繪制矢量圖層 QString Image_Path = QFileDialog::getOpenFileName(this,tr("Select"),"D:/svg",tr("Files(*.svg)")); QgsSvgMarkerSymbolLayer* svg_Marker = new QgsSvgMarkerSymbolLayer(Image_Path);
svg_Marker->setColor(QColor(0,0,0));
svg_Marker->setSize(10);
svg_Marker->setAngle(0); //創建QgsSymbolLayerList QgsSymbolLayerList Sym_Layer_List; Sym_Layer_List.append(svg_Marker); //構建QgsMarkerSymbol QgsMarkerSymbol* MarkerSymbol = new QgsMarkerSymbol(Sym_Layer_List); //構建QgsSingleSymbolRenderer, 即最終圖層的渲染器 QgsSingleSymbolRenderer* Sym_Renderer = new QgsSingleSymbolRenderer( MarkerSymbol ); //設置當前圖層的渲染器 CurrentLayer->setRenderer(Sym_Renderer);
// My_MapCanvas->freeze(false); My_MapCanvas->refresh();
設置線樣式（線圖層渲染 QgsFeatureRenderer）
My_MapCanvas->freeze();
//設置線圖層的樣式，包括color, width (in millimeters) and penStyle QgsSimpleLineSymbolLayer* Line_Renderer_Layer = new QgsSimpleLineSymbolLayer(); Line_Renderer_Layer->setColor(Qt::red); Line_Renderer_Layer->setPenStyle(Qt::PenStyle::DotLine); //創建矢量圖層列表,QgsSymbolLayerList就是重新定義了一個特殊的QList QgsSymbolLayerList Sym_Layer_List; Sym_Layer_List.append(Line_Renderer_Layer); //構建QgsLineSymbol QgsLineSymbol* LineSymbol = new QgsLineSymbol(Sym_Layer_List); //構建QgsSingleSymbolRenderer, 即最終圖層的渲染器 QgsSingleSymbolRenderer* Sym_Renderer = new QgsSingleSymbolRenderer( LineSymbol ); //設置當前圖層的渲染器 CurrentLayer->setRenderer( Sym_Renderer );
//
My_MapCanvas->freeze(false);
My_MapCanvas->refresh();
在圖層中添加標簽，顯示某字段屬性
QgsVectorLayer* vLayer = new QgsVectorLayer("D:/MSCities_Geo_Pts.shp", "Cities", "ogr"); //文本緩沖區設置 QgsTextBufferSettings* bufSettings = new QgsTextBufferSettings; bufSettings->setEnabled(true); //啟用文本緩沖區 bufSettings->setSize(1); //設置緩緩沖區大小 bufSettings->setColor(QColor("white")); //文本樣式設置 QgsTextFormat * textFormat = new QgsTextFormat; textFormat->setFont( QFont("Arial", 12) ); textFormat->setSize(12); textFormat->setBuffer(*bufSettings); //設置文本緩沖區 //圖層屬性設置 QgsPalLayerSettings* lSettings = new QgsPalLayerSettings; lSettings->setFormat(*textFormat); //設置標簽文本格式 lSettings->fieldName = "NAME10"; //要顯示的字段名 lSettings->placement = QgsPalLayerSettings::Placement::Line; //設置標簽樣式 //lSettings->geometryGeneratorEnabled = true; //啟用幾何生成器 //創建label標簽 QgsVectorLayerSimpleLabeling* LSsettings = new QgsVectorLayerSimpleLabeling(*lSettings); // vLayer->setLabelsEnabled(true); //該圖層啟用label標簽 vLayer->setLabeling(LSsettings); //設置標簽配置 vLayer->triggerRepaint();
遍歷元素及元素字段
QgsFeatureIterator it = vLayer->getFeatures(); it->rewind(); QgsFeature f; while( it.nextFeature(f) ) { //f.attribute(fieldsID).toInt(); }
查詢元素時，常用到矢量圖層的QgsFeatureRequest
參考鏈接：QT(5.12)+Qgis(3.10) 點圖層及線圖層渲染 - 灰信網（軟件開發博客聚合） (freesion.com)