一. 前言
作为编程菜鸡，我有事没事都会上Github上抄代码。
基本上想写点东西时，都会先在Github上看有没有现成的......
又因为写的代码往往和GIS相关，GIS又是个炒鸡冷门的方向，所以往往搜索结果惨淡，拉下来能用的代码更是寥寥无几呀。
这时候就只能在别人代码基础上修改了，愁......
该Github项目的地址
https://github.com/substack/shp2json
二. 修改
当初是想实现一个将shapefile文件转为json的功能，
在Github上类似的代码还算多。
但是，作为菜鸡，那么多的代码里，我能运行的也就那么一两个，再从中间挑一个评分高的，那就选中shp2json了。
作为菜鸡，真的心累。
在运行完shp2json，发现json数据能正确显示在控制台里。
那么呵呵呵，怎么把控制台的所谓的“流”变成json字符串呢？
这对连json是什么都不知道的我真是头大呀。
当时各种搜索，各种关键词都一无所获，
最后走投无路时只能打开源码。
其实我连源码怎么看都不知道，
但还好，所以就挑了个最长最大的index.js开始瞎几把改。
最后，就莫名其妙的成功了。
呵呵呵~
下面是代码修改：
原来的index.js
1 function fromShpFile (file, outStream) { 2 ????outStream = outStream || duplex.obj(); 3 ????var shp = gdal.open(file); 4 ????var layerCount = shp.layers.count(); 5 ?6 ????var before = ‘{"type": "FeatureCollection","features": [\n‘; 7 ????var after = ‘\n]}\n‘; 8 ????var started = false; 9 ????var currentLayer, currentFeature, currentTransformation;10 ????var nextLayer = 0;11 12 ????var to = gdal.SpatialReference.fromEPSG(4326);13 14 ????function getNextLayer() {15 ??????currentLayer = shp.layers.get(nextLayer++);16 ??????var srs = currentLayer.srs || gdal.SpatialReference.fromEPSG(4326);17 ??????currentTransformation = new gdal.CoordinateTransformation(srs, to);18 ????}19 20 ????getNextLayer();21 22 ????var layerStream = from(function(size, next) {23 ??????var out = ‘‘;24 ??????writeNextFeature();25 26 ??????function writeNextFeature() {27 ??????????var feature = currentLayer.features.next();28 ??????????if (!feature) {29 ??????????????// end stream30 ??????????????if (nextLayer === layerCount) {31 ??????????????????// push remaining output and end32 ??????????????????layerStream.push(out);33 ??????????????????layerStream.push(after);34 ??????????????????return layerStream.push(null);35 ??????????????}36 ??????????????getNextLayer();37 ??????????????feature = currentLayer.features.next();38 ??????????}39 40 ??????????try {41 ??????????????var geom = feature.getGeometry();42 ??????????} catch (e) {43 ??????????????return writeNextFeature();44 ??????????}45 46 ??????????geom.transform(currentTransformation);47 ??????????var geojson = geom.toJSON();48 ??????????var fields = feature.fields.toJSON();49 ??????????var featStr = ‘{"type": "Feature", "properties": ‘ + fields + ‘,"geometry": ‘ + geojson + ‘}‘;50 51 ??????????if (started) {52 ??????????????featStr = ‘,\n‘ + featStr;53 ??????????} else {54 ??????????????featStr = before + featStr;55 ??????????}56 57 ??????????started = true;58 ??????????out += featStr;59 60 ??????????if (out.length >= size) {61 ??????????????next(null, out);62 ??????????} else {63 ??????????????writeNextFeature();64 ??????????}65 ??????}66 67 ????})68 69 ????outStream.setReadable(layerStream);70 ????outStream.end(after);71 72 ????return outStream;73 }修改之后的代码：
1 function fromShpFile (file, outStream) { 2 ????var out = ‘‘; 3 ????outStream = outStream || duplex.obj(); 4 ????var shp = gdal.open(file); 5 ????var layerCount = shp.layers.count(); 6 ?????7 ????var countLimit = 0;//要素读取数量限制 8 ?????9 ????var before = ‘{"type": "FeatureCollection","features": [\n‘;10 ????var after = ‘\n]}\n‘;11 ????var started = false;12 ????var currentLayer, currentFeature, currentTransformation;13 ????var nextLayer = 0;14 15 ????var to = gdal.SpatialReference.fromEPSG(4326);16 17 ????function getNextLayer() {18 ??????currentLayer = shp.layers.get(nextLayer++);19 ??????var srs = currentLayer.srs || gdal.SpatialReference.fromEPSG(4326);20 ??????currentTransformation = new gdal.CoordinateTransformation(srs, to);21 ????}22 23 ????getNextLayer();24 25 ????var layerStream = from(function(size, next) {26 ??????writeNextFeature();27 28 ??????function writeNextFeature() {29 ??????????var feature = currentLayer.features.next();30 ??????????if (!feature) {31 ??????????????// end stream32 ??????????????if (nextLayer === layerCount) {33 ??????????????????// push remaining output and end34 ??????????????????layerStream.push(out);35 ??????????????????layerStream.push(after);36 ??????????????????return layerStream.push(null);37 ??????????????}38 ??????????????getNextLayer();39 ??????????????feature = currentLayer.features.next();40 ??????????}41 42 ??????????try {43 ??????????????var geom = feature.getGeometry();44 ??????????} catch (e) {45 ??????????????return writeNextFeature();46 ??????????}47 48 ??????????geom.transform(currentTransformation);49 ??????????var geojson = geom.toJSON();50 ??????????var fields = feature.fields.toJSON();51 ??????????var featStr = ‘{"type": "Feature", "properties": ‘ + fields + ‘,"geometry": ‘ + geojson + ‘}‘;52 53 ??????????if (started) {54 ??????????????featStr = ‘,\n‘ + featStr;55 ??????????} else {56 ??????????????featStr = before + featStr;57 ??????????}58 59 ??????????started = true;60 ??????????out += featStr;61 62 ?????????countLimit++; ?//要素读取数量63 ??????????????????64 ?????????if(countLimit < 8000)65 ????????????writeNextFeature(); ?//这个方法报错,栈溢出66 67 ??????}68 69 ????})70 71 ????outStream.setReadable(layerStream);72 ????outStream.end(after);73 74 ????return (out += after) ; ?75 }三. 问题
这个包转为的速率并不理想，甚至很慢......
而且当要素数量过大时，会栈溢出，这和机器的内存有关......
当然我也束手无策，
所以，呵呵哒。
[Github]shapefile转json——对Github上shp2json项目的修改
原文地址：https://www.cnblogs.com/KissXuan/p/9839421.html