GIS开发：geojson图层批量坐标转换
在没有规律的坐标偏移情况下，如国内在线地图偏移和经纬度转换，可以进行方便进行单个坐标的转换，转换图层就需要自己进行开发了。
感谢coordtransform库的作者，这里使用了coordtransform进行偏移坐标的转换。
//引入fs和coordtransform库
const fs = require('fs');
const coordtransform = require('coordtransform');
//geojson矢量对象处理
function dataByfeaturetype(_feature) {
this.datafeature = _feature;
this.featuretype = _feature.geometry.type;
this.coords = _feature.geometry.coordinates;
this.newcoords = [];
}
//点、线、面中数据坐标遍历处理
dataByfeaturetype.prototype.handlePoint = function () {
this.newcoords = coordtransform.wgs84togcj02(this.coords[0], this.coords[1]);
}
dataByfeaturetype.prototype.handleMultipointOrLinestring = function () {
let _tempCoords = [];
for (let _udx = 0; _udx < this.coords.length; _udx++) {
//这个根据自己的需要，选择坐标的偏移处理函数
_tempCoords.push(coordtransform.wgs84togcj02(this.coords[_udx][0], this.coords[_udx][1]));
}
this.newcoords = _tempCoords;
}
dataByfeaturetype.prototype.handleMultiLineStringOrPolygon = function () {
let _tempCoords = [];
for (let _udx = 0; _udx < this.coords.length; _udx++) {
let _evCoords = [];
for (let _ndx = 0; _ndx < this.coords[_udx].length; _ndx++) {
//这个根据自己的需要，选择坐标的偏移处理函数
_evCoords.push(coordtransform.wgs84togcj02(this.coords[_udx][_ndx][0], this.coords[_udx][_ndx][1]));
}
_tempCoords.push(_evCoords);
}
this.newcoords = _tempCoords;
}
dataByfeaturetype.prototype.handleMultiPolygon = function () {
let _tempCoords = [];
for (let _udx = 0; _udx < this.coords.length; _udx++) {
let _polygons = [];
for (let _ndx = 0; _ndx < this.coords[_udx].length; _ndx++) {
let _polygon = [];
for (let _tdx = 0; _tdx < this.coords[_udx][_ndx].length; _tdx++) {
_polygon.push(coordtransform.wgs84togcj02(this.coords[_udx][_ndx][_tdx][0], this.coords[_udx][_ndx][_tdx][1]));
}
_polygons.push(_polygon);
}
_tempCoords.push(_polygons);
}
this.newcoords = _tempCoords;
}
//根据图层的不同类型，选择处理方法
dataByfeaturetype.prototype.handleByType = function () {
switch (this.featuretype) {
case "Point":
this.handlePoint();
break;
case "MultiPoint":
case "LineString":
this.handleMultipointOrLinestring();
break;
case "MultiLineString":
case "Polygon":
this.handleMultiLineStringOrPolygon();
break;
case "MultiPolygon":
this.handleMultiPolygon();
break;
}
}
//获取数据处理结果
dataByfeaturetype.prototype.getResult = function () {
this.datafeature.geometry.coordinates = this.newcoords;
return this.datafeature;
};
//输入文件
fs.readFile('输入geojson文件', {
encoding: 'utf-8'
}, (err, res) => {
if (err) return;
let _geojsondata = JSON.parse(res);
let _newfeatures = [];
let _features = _geojsondata.features;
for (let _fdx = 0; _fdx < _features.length; _fdx++) {
let _feature = _features[_fdx];
let _featurehandle = new dataByfeaturetype(_feature);
_featurehandle.handleByType();
_newfeatures.push(_featurehandle.getResult());
}
_geojsondata.features = _newfeatures;
//输出处理结果
fs.writeFile("输出geojson", JSON.stringify(_geojsondata), (err) => {
console.log(err);
});
});
