openlayers测距和测面积

 初次使用openlayers地图进行开发各种地图功能，测距和测面积使用的是官方例子并进行了一些简单的修改，官方示例在测量一次之后不能停止，修改后，每点击测量，只会测量一次。

而且需要注意的是，官方例子测距测面积使用的投影坐标系是3857。

js文件：measure.js

import Draw from 'ol/interaction/Draw'
import VectorSource from 'ol/source/Vector';
import VectorLayer from 'ol/layer/Vector';
import TileLayer from 'ol/layer/Tile';
import OSM from 'ol/source/OSM';

import {
  unByKey
} from 'ol/Observable.js';
import Overlay from 'ol/Overlay';
import {
  getArea,
  getLength
} from 'ol/sphere.js';
import View from 'ol/View';
import {
  LineString,
  Polygon
} from 'ol/geom.js';
import {
  Circle as CircleStyle,
  Fill,
  Stroke,
  Style,
  Text
} from 'ol/style.js';
export default{

  measure(map, measureType) {
    var source = new VectorSource();

    var vector = new VectorLayer({
      id:'lineAndArea',
      source: source,
      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'
          })
        })
      }),
      zIndex:16
    });
    map.addLayer(vector)
    /**
     * Currently drawn feature.
     * @type {module:ol/Feature~Feature}
     */
    var sketch;


    /**
     * The help tooltip element.
     * @type {Element}
     */
    var helpTooltipElement;


    /**
     * Overlay to show the help messages.
     * @type {module:ol/Overlay}
     */
    var helpTooltip;


    /**
     * The measure tooltip element.
     * @type {Element}
     */
    var measureTooltipElement;


    /**
     * Overlay to show the measurement.
     * @type {module:ol/Overlay}
     */
    var measureTooltip;


    /**
     * Message to show when the user is drawing a polygon.
     * @type {string}
     */
    var continuePolygonMsg = '继续点击绘制多边形';


    /**
     * Message to show when the user is drawing a line.
     * @type {string}
     */
    var continueLineMsg = '继续点击绘制线';



    /**
     * Handle pointer move.
     * @param {module:ol/MapBrowserEvent~MapBrowserEvent} evt The event.
     */
    var pointerMoveHandler = function (evt) {
      if (evt.dragging) {
        return;
      }
      /** @type {string} */
      var helpMsg = '请点击开始绘制';

      if (sketch) {
        var geom = sketch.getGeometry();
        if (geom instanceof Polygon) {
          helpMsg = continuePolygonMsg;
        } else if (geom instanceof LineString) {
          helpMsg = continueLineMsg;
        }
      }

      helpTooltipElement.innerHTML = helpMsg;
      helpTooltip.setPosition(evt.coordinate);

      helpTooltipElement.classList.remove('hidden');
    };

    map.on('pointermove', pointerMoveHandler);

    map.getViewport().addEventListener('mouseout', function () {
      helpTooltipElement.classList.add('hidden');
    });

    var draw;
    var formatLength = function (line) {
      //获取投影坐标系
      var sourceProj = map.getView().getProjection();
      //ol/sphere里有getLength()和getArea()用来测量距离和区域面积，默认的投影坐标系是EPSG:3857, 其中有个options的参数，可以设置投影坐标系
      var length = getLength(line, {projection: sourceProj});
      //var length = getLength(line);
      var output;
      if (length > 100) {
        output = (Math.round(length / 1000 * 100) / 100) +
          ' ' + 'km';
      } else {
        output = (Math.round(length * 100) / 100) +
          ' ' + 'm';
      }
      return output;
    };
    var formatArea = function (polygon) {
      //获取投影坐标系
      var sourceProj = map.getView().getProjection();
      var area = getArea(polygon, {projection: sourceProj})
      //var area = getArea(polygon);
      //console.info(area)
      var output;
      if (area > 10000) {
        output = (Math.round(area / 1000000 * 100) / 100) +
          ' ' + 'km<sup>2</sup>';
      } else {
        output = (Math.round(area * 100) / 100) +
          ' ' + 'm<sup>2</sup>';
      }
      return output;
    };

    function addInteraction() {
      draw = new Draw({
        source: source,
        type: measureType,
        style: new Style({
          fill: new Fill({
            color: 'rgba(255, 255, 255, 0.2)'
          }),
          stroke: new Stroke({
            color: 'rgba(0, 0, 0, 0.5)',
            lineDash: [10, 10],
            width: 2
          }),
          image: new CircleStyle({
            radius: 5,
            stroke: new Stroke({
              color: 'rgba(0, 0, 0, 0.7)'
            }),
            fill: new Fill({
              color: 'rgba(255, 255, 255, 0.2)'
            })
          })
        })
      });
      map.addInteraction(draw);

      createMeasureTooltip();
      createHelpTooltip();

      var listener;
      draw.on('drawstart',
        function (evt) {
          // set sketch
          sketch = evt.feature;

          /** @type {module:ol/coordinate~Coordinate|undefined} */
          var tooltipCoord = evt.coordinate;

          listener = sketch.getGeometry().on('change', function (evt) {
            var geom = evt.target;
            var output;
            if (geom instanceof Polygon) {
              output = formatArea(geom);
              tooltipCoord = geom.getInteriorPoint().getCoordinates();
            } else if (geom instanceof LineString) {
              output = formatLength(geom);
              tooltipCoord = geom.getLastCoordinate();
            }
            measureTooltipElement.innerHTML = output;
            measureTooltip.setPosition(tooltipCoord);
          });
        }, this);

      draw.on('drawend',
        function () {
          measureTooltipElement.className = 'ol-tooltip ol-tooltip-static measureNum';
          measureTooltip.setOffset([0, -7]);
          // unset sketch
          sketch = null;
          // unset tooltip so that a new one can be created
          measureTooltipElement = null;
          createMeasureTooltip();
          unByKey(listener);
          map.un('pointermove', pointerMoveHandler);
          map.removeInteraction(draw);
          helpTooltipElement.classList.add('hidden');
          //console.info(helpTooltipElement.classList)
        }, this);
    }

    function createHelpTooltip() {
      if (helpTooltipElement) {
        helpTooltipElement.parentNode.removeChild(helpTooltipElement);
      }
      helpTooltipElement = document.createElement('div');
      helpTooltipElement.className = 'ol-tooltip hidden';
      helpTooltip = new Overlay({
        element: helpTooltipElement,
        offset: [15, 0],
        positioning: 'center-left'
      });
      map.addOverlay(helpTooltip);
    }

    function createMeasureTooltip() {
      if (measureTooltipElement) {
        measureTooltipElement.parentNode.removeChild(measureTooltipElement);
      }
      measureTooltipElement = document.createElement('div');
      measureTooltipElement.className = 'ol-tooltip ol-tooltip-measure';
      measureTooltip = new Overlay({
        element: measureTooltipElement,
        offset: [0, -15],
        positioning: 'bottom-center'
      });
      map.addOverlay(measureTooltip);
    }
    // 量测调用
    addInteraction();
  }
}

在文件中调用：

      首先引入js文件：

     调用方法：

 

 效果展示：

注：还有一种实现测距，测面积的方法，就是使用turf.js，不过具体使用没有深入研究，等有机会，再去深入了解一下。