vue openlayers 绘制区域面

要在 Vue 中使用 OpenLayers 绘制区域面，需要先安装 OpenLayers 和 ol-ext 库。然后按照以下步骤进行操作：

1. 在 Vue 组件中引入所需库：

import 'ol/ol.css';
import 'ol-ext/dist/ol-ext.css';
import { Map, View } from 'ol';
import { Draw, Modify, Snap } from 'ol/interaction';
import { Vector as VectorSource } from 'ol/source';
import { Vector as VectorLayer } from 'ol/layer';
import { Fill, Stroke, Style } from 'ol/style';
import { Circle as CircleStyle } from 'ol/style';
import { defaults as defaultControls, ScaleLine } from 'ol/control';
import { Extent, getCenter } from 'ol/extent';
import { bbox as bboxStrategy } from 'ol/loadingstrategy';
import { bbox as bboxFilter } from 'ol/format/filter';
import { transform } from 'ol/proj';
import { unByKey } from 'ol/Observable';
import { LayerSwitcher } from 'ol-ext/control';
import { GeoJSON } from 'ol/format';

2. 在 Vue 组件的 `mounted` 钩子中创建地图、图层、交互和样式：

mounted() {
  // 创建地图
  this.map = new Map({
    target: 'map',
    layers: [
      new TileLayer({
        source: new XYZ({
          url: 'https://{a-c}.tile.openstreetmap.org/{z}/{x}/{y}.png'
        })
      }),
      this.vectorLayer
    ],
    view: new View({
      projection: 'EPSG:4326',
      center: [0, 0],
      zoom: 2
    }),
    controls: defaultControls().extend([
      new ScaleLine(),
      new LayerSwitcher()
    ])
  });

  // 创建矢量图层
  this.vectorSource = new VectorSource();
  this.vectorLayer = new VectorLayer({
    source: this.vectorSource,
    style: new Style({
      fill: new Fill({
        color: 'rgba(255, 255, 255, 0.2)'
      }),
      stroke: new Stroke({
        color: '#ffcc33',
        width: 2
      }),
      image: new CircleStyle({
        radius: 7,
        fill: new Fill({
          color: '#ffcc33'
        })
      })
    })
  });

  // 创建绘制交互
  this.draw = new Draw({
    source: this.vectorSource,
    type: 'Polygon'
  });

  // 创建修改交互
  this.modify = new Modify({
    source: this.vectorSource
  });

  // 创建捕捉交互
  this.snap = new Snap({
    source: this.vectorSource
  });

  // 添加绘制和修改交互
  this.map.addInteraction(this.draw);
  this.map.addInteraction(this.modify);
  this.map.addInteraction(this.snap);

  // 监听绘制结束事件
  this.draw.on('drawend', (event) => {
    const feature = event.feature;
    const geometry = feature.getGeometry();
    const format = new GeoJSON();
    const geojson = format.writeGeometry(geometry);
    console.log(geojson);
  });
},

3. 在 Vue 组件的模板中创建地图容器：

<template>
  <div id="map"></div>
</template>

4. 现在你可以开始在地图上绘制区域面了。当绘制结束后，会在控制台输出 GeoJSON 格式的几何信息。

注意：在使用 OpenLayers 绘制区域面时，需要注意地图的投影方式和坐标系，以及几何图形的坐标系转换。