GIS开发：geojson图层批量坐标转换

原创

GIS技术杂谈 2022-09-27 16:28:56 ©著作权

文章标签 json 图层 git 文章分类 运维

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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);
    });
});