标签：关键词 src new gdal before UNC 素数 项目 alt
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 stream 30 if (nextLayer === layerCount) { 31 // push remaining output and end 32 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 stream 32 if (nextLayer === layerCount) { 33 // push remaining output and end 34 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
标签：关键词 src new gdal before UNC 素数 项目 alt
原文地址：https://www.cnblogs.com/KissXuan/p/9839421.html
