使用openlayers进行空间分析的方法——JSTS库的应用

查看openlayers文档可以发现，openlayers中进行缓冲区分析的方法只有一个，这个方法只适合扩展矩形缓冲区，如果想扩展任意形状的缓冲区则需要用到JSTS。

ol.extent.buffer(extent, value, opt_extent)

 例如下面的例子实现了对点【0,0】扩展缓冲区

var pointFeature = new ol.Feature(new ol.geom.Point([0, 0]));
var vectorPoint = new ol.layer.Vector({
    source: new ol.source.Vector({
        features: [pointFeature]
    })
});
var vectorBuffers = new ol.layer.Vector({
    source: new ol.source.Vector({})
});
var map = new ol.Map({
    layers: [vectorPoint, vectorBuffers],
    target: 'map',
    view: new ol.View({
        center: [0, 0],
        zoom: 2
    })
});
var radius = 1000000;

function bufferit(radius) {
    var poitnExtent = pointFeature.getGeometry().getExtent();
    var bufferedExtent = new ol.extent.buffer(poitnExtent, radius);
    console.log(bufferedExtent);
    var bufferPolygon = new ol.geom.Polygon([
        [
            [bufferedExtent[0], bufferedExtent[1]],
            [bufferedExtent[0], bufferedExtent[3]],
            [bufferedExtent[2], bufferedExtent[3]],
            [bufferedExtent[2], bufferedExtent[1]],
            [bufferedExtent[0], bufferedExtent[1]]
        ]
    ]);
    console.log("bufferPolygon", bufferPolygon);
    var bufferedFeature = new ol.Feature(bufferPolygon);
    vectorBuffers.getSource().addFeature(bufferedFeature)
}

 

JSTS是一个符合OGC规范的简单要素空间位置判定函数JavaScript库，JSTS也是Java类库JTS的一个接口，且与OpenLayer具有互操作性。 下面是JSTS官方例子：
 

使用WKT format读取A和B两个点

var reader = new jsts.io.WKTReader()
var a = reader.read('POINT (-20 0)')
var b = reader.read('POINT (20 0)')
将A点和B点进行40单位的缓冲区分析
a = a.buffer(40)
b = b.buffer(40)

A和B进行相交分析

var intersection = a.intersection(b)
A异同B分析

var difference = a.difference(b)
A合并B

var union = a.union(b)
A、B对称异同
var symDifference = a.symDifference(b)

 参考http://bjornharrtell.github.io/jsts/

openlayers中也可以直接使用JSTS进行空间分析，如下面的例子：

  
    
    
    
    
    
  
  
    

    
  

import 'ol/ol.css';
import Map from 'ol/Map';
import View from 'ol/View';
import GeoJSON from 'ol/format/GeoJSON';
import {Tile as TileLayer, Vector as VectorLayer} from 'ol/layer';
import {fromLonLat} from 'ol/proj';
import OSM from 'ol/source/OSM';
import VectorSource from 'ol/source/Vector';
import LinearRing from 'ol/geom/LinearRing';
import {Point, LineString, Polygon, MultiPoint, MultiLineString, MultiPolygon} from 'ol/geom';

var source = new VectorSource();
fetch('data/geojson/roads-seoul.geojson').then(function(response) {
  return response.json();
}).then(function(json) {
  var format = new GeoJSON();
  var features = format.readFeatures(json, {featureProjection: 'EPSG:3857'});

  var parser = new jsts.io.OL3Parser();
  parser.inject(Point, LineString, LinearRing, Polygon, MultiPoint, MultiLineString, MultiPolygon);

  for (var i = 0; i < features.length; i++) {
    var feature = features[i];
    // convert the OpenLayers geometry to a JSTS geometry
    var jstsGeom = parser.read(feature.getGeometry());

    // create a buffer of 40 meters around each line
    var buffered = jstsGeom.buffer(40);

    // convert back from JSTS and replace the geometry on the feature
    feature.setGeometry(parser.write(buffered));
  }

  source.addFeatures(features);
});
var vectorLayer = new VectorLayer({
  source: source
});

var rasterLayer = new TileLayer({
  source: new OSM()
});

var map = new Map({
  layers: [rasterLayer, vectorLayer],
  target: document.getElementById('map'),
  view: new View({
    center: fromLonLat([126.979293, 37.528787]),
    zoom: 15
  })
});

运行结果如下：