8.12 矢量图层面要素单一符号使用八(随机标记填充)_qgis随机填充-CSDN博客
目录
[随机标记填充(Random Marker Fill)](#随机标记填充(Random Marker Fill))
[QGis设置面符号为随机标记填充(Random Marker Fill)](#QGis设置面符号为随机标记填充(Random Marker Fill))
[二次开发代码实现随机标记填充(Random Marker Fill)](#二次开发代码实现随机标记填充(Random Marker Fill))
前言
- 本章介绍矢量图层线要素单一符号中使用随机标记填充(Random Marker Fill)的使用
- 说明:文章中的示例代码均来自开源项目qgis_cpp_api_apps
随机标记填充(Random Marker Fill)
A fill symbol layer which places markers at random locations within polygons.
- 以protected_areas.shp为例,图层符号为Simple Fill时显示效果如下图

QGis设置面符号为随机标记填充(Random Marker Fill)
- Symbol layer type设置为Random Marker Fill,可设置的属性如下图

Marker Fill需要设置其子符号,子符号类型为Marker
- 属性设置完成后,图层显示效果如下图

二次开发代码实现随机标记填充(Random Marker Fill)
- 类
QgsRandomMarkerFillSymbolLayer
是Random Marker Fill,详情见文档,类图如下

- 函数
setSubSymbol (QgsSymbol *symbol)
可以设置子符号 - 创建符号层有两种方法:构造函数和
create
- 方法一
- 从图层获取渲染器
cpp
//从图层获取渲染器
QgsFeatureRenderer * layerRenderer= layer->renderer();
QgsSingleSymbolRenderer *singleSymbolRenderer = QgsSingleSymbolRenderer::convertFromRenderer(layerRenderer);
- 构造函数:修改属性可以调用setxxx函数,如下代码
cpp
int pointCount = 100;
auto randomMarkerFillSymbolLayer = new QgsRandomMarkerFillSymbolLayer(100);
randomMarkerFillSymbolLayer->setDensityArea(250.0);
randomMarkerFillSymbolLayer->setCountMethod(Qgis::PointCountMethod::Absolute);
- 创建符号并设置到渲染器
cpp
//多个Symbol Layer构成一个Symbol
QgsSymbolLayerList layerList;
layerList << randomMarkerFillSymbolLayer;
//构造QgsFillSymbol并设置renderer
auto fillSymbol = new QgsFillSymbol(layerList);
singleSymbolRenderer->setSymbol(fillSymbol);
layer->setRenderer(singleSymbolRenderer);
- 方法二
方法一中步骤1,3不变,步骤2中使用create()
成员函数,颜色方案同样有两种选择
cpp
QVariantMap mp;
mp["point_count"] = QStringLiteral("100");
mp["density_area"] = QStringLiteral("250.0");
mp["count_method"] = QStringLiteral("0");
auto randomMarkerFillSymbolLayer = QgsRandomMarkerFillSymbolLayer::create(mp);
- 完整测试代码如下
cpp
void MainWindow::polygonRandomMarkerSlot()
{
//添加一个线图层
QgsVectorLayer* layer = addTestShape(QStringLiteral("maps/shapefile/protected_areas.shp"));
//从图层获取渲染器
QgsFeatureRenderer * layerRenderer= layer->renderer();
QgsSingleSymbolRenderer *singleSymbolRenderer = QgsSingleSymbolRenderer::convertFromRenderer(layerRenderer);
#if 1
int pointCount = 100;
auto randomMarkerFillSymbolLayer = new QgsRandomMarkerFillSymbolLayer(100);
randomMarkerFillSymbolLayer->setDensityArea(250.0);
randomMarkerFillSymbolLayer->setCountMethod(Qgis::PointCountMethod::Absolute);
#else
QVariantMap mp;
mp["point_count"] = QStringLiteral("100");
mp["density_area"] = QStringLiteral("250.0");
mp["count_method"] = QStringLiteral("0");
auto randomMarkerFillSymbolLayer = QgsRandomMarkerFillSymbolLayer::create(mp);
#endif
//多个Symbol Layer构成一个Symbol
QgsSymbolLayerList layerList;
layerList << randomMarkerFillSymbolLayer;
//构造QgsFillSymbol并设置renderer
auto fillSymbol = new QgsFillSymbol(layerList);
singleSymbolRenderer->setSymbol(fillSymbol);
layer->setRenderer(singleSymbolRenderer);
}
- 效果如下图


总结
- 介绍了矢量图层面要素单一符号中的随机标记填充(Random Marker Fill)