It is the first time to use openlayers maps to develop various map functions. The official examples are used for distance measurement and area measurement with some simple modifications. The official examples cannot be stopped after one measurement. After the modification, each click to measure will only measure once.
And it should be noted that the projected coordinate system used in the official example of ranging and area measurement is 3857.
js file: 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();
}
}Call in the file:
First introduce the js file:
Calling method:
Show results:
Note: There is another way to achieve distance measurement and area measurement, which is to use turf.js, but the specific use has not been studied in depth. When there is a chance, I will learn more.