绘制图形要素（Feature）

几何类型:

本示例演示 ol/interaction/Draw 交互.

本示例演示 Draw 交互的使用。首先在下拉框选择一个几何类型，然后开始绘制。可以通过点击最后一个点，来结束绘制（或者双击）。可以通过按住 Shift 键，来开启线、面和圆的自由绘制操作。如果想移除上一个点，可以点击 "取消上一个点" 按钮。

main.js

import Draw from 'ol/interaction/Draw.js';
import Map from 'ol/Map.js';
import View from 'ol/View.js';
import {OSM, Vector as VectorSource} from 'ol/source.js';
import {Tile as TileLayer, Vector as VectorLayer} from 'ol/layer.js';

const raster = new TileLayer({
  source: new OSM(),
});

const source = new VectorSource({wrapX: false});

const vector = new VectorLayer({
  source: source,
});

const map = new Map({
  layers: [raster, vector],
  target: 'map',
  view: new View({
    center: [-11000000, 4600000],
    zoom: 4,
  }),
});

const typeSelect = document.getElementById('type');

let draw; // global so we can remove it later
function addInteraction() {
  const value = typeSelect.value;
  if (value !== 'None') {
    draw = new Draw({
      source: source,
      type: typeSelect.value,
    });
    map.addInteraction(draw);
  }
}

/**
 * Handle change event.
 */
typeSelect.onchange = function () {
  map.removeInteraction(draw);
  addInteraction();
};

document.getElementById('undo').addEventListener('click', function () {
  draw.removeLastPoint();
});

addInteraction();

index.html

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8">
    <title>Draw Features</title>
    <link rel="stylesheet" href="./resources/bootstrap.min.css">
    <link rel="stylesheet" href="node_modules/ol/ol.css">
    <style>
      .map {
        width: 100%;
        height: 400px;
      }
    </style>
  </head>
  <body>
    <div id="map" class="map"></div>
    <div class="row">
      <div class="col-auto">
        <span class="input-group">
          <label class="input-group-text" for="type">Geometry type:</label>
          <select class="form-select" id="type">
            <option value="Point">Point</option>
            <option value="LineString">LineString</option>
            <option value="Polygon">Polygon</option>
            <option value="Circle">Circle</option>
            <option value="None">None</option>
          </select>
          <input class="form-control" type="button" value="Undo" id="undo">
        </span>
      </div>
    </div>
    <!-- Pointer events polyfill for old browsers, see https://caniuse.com/#feat=pointer -->
    <script src="./resources/elm-pep.js"></script>
    <script type="module" src="main.js"></script>
  </body>
</html>

package.json

{
  "name": "draw-features",
  "dependencies": {
    "ol": "7.3.0"
  },
  "devDependencies": {
    "vite": "^3.2.3"
  },
  "scripts": {
    "start": "vite",
    "build": "vite build"
  }
}