Convert coordinates to WGS 84 base on the .prj file

bin/shp2json

@@ -2,7 +2,8 @@
 
 var fs = require("fs"),
     commander = require("commander"),
-    shapefile = require("../");
+    shapefile = require("../"),
+    proj4 = require('proj4');
 
 commander
     .version(require("../package.json").version)
@@ -26,10 +27,18 @@ else if (commander.args.length !== 1) {
 
 var out = (commander.out === "-" ? process.stdout : fs.createWriteStream(commander.out)).on("error", handleEpipe);
 
+// My addition to read prj file, turn it into a function that I will apply to all coordinates
+var shpFilename = commander.args[0],
+    prjFilename = shpFilename.substring(0, shpFilename.length - 4) + ".prj",
+    prjStr = fs.readFileSync(prjFilename).toString(),
+    prj = proj4(prjStr),
+    xform = prj.inverse.bind(prj);
+// end for now, but `xform` will be passed around
+
 shapefile.open(
     commander.args[0] === "-" ? process.stdin : commander.args[0],
     commander.geometry || commander.ignoreProperties ? null : undefined,
-    {encoding: commander.encoding})
+    {encoding: commander.encoding, xform: xform})
   .then(commander.newlineDelimited
       ? (commander.geometry ? writeNewlineDelimitedGeometries : writeNewlineDelimitedFeatures)
       : (commander.geometry ? writeGeometryCollection : writeFeatureCollection))

index.js

@@ -26,7 +26,7 @@ export function open(shp, dbf, options) {
   return Promise.all([shp, dbf]).then(function(sources) {
     var shp = sources[0], dbf = sources[1], encoding = "windows-1252";
     if (options && options.encoding != null) encoding = options.encoding;
-    return shapefile(shp, dbf, dbf && new TextDecoder(encoding));
+    return shapefile(shp, dbf, dbf && new TextDecoder(encoding), options ? options.xform : function (x) {x});
   });
 }
 

package.json

@@ -34,13 +34,14 @@
     "array-source": "0.0",
     "commander": "2",
     "path-source": "0.1",
+    "proj4": "2.7.0",
     "slice-source": "0.4",
     "stream-source": "0.3",
     "text-encoding": "^0.6.4"
   },
   "devDependencies": {
     "package-preamble": "0.1",
-    "rollup": "0.49",
+    "rollup": "^0.49.3",
     "rollup-plugin-node-resolve": "3",
     "tape": "4",
     "uglify-js": "3"

shapefile/index.js

@@ -3,9 +3,9 @@ import shp from "../shp/index";
 import shapefile_cancel from "./cancel";
 import shapefile_read from "./read";
 
-export default function(shpSource, dbfSource, decoder) {
+export default function(shpSource, dbfSource, decoder, xform) {
   return Promise.all([
-    shp(shpSource),
+    shp(shpSource, xform),
     dbfSource && dbf(dbfSource, decoder)
   ]).then(function(sources) {
     return new Shapefile(sources[0], sources[1]);

shp/index.js

@@ -24,21 +24,24 @@ var parsers = {
   28: parseMultiPoint // MultiPointM
 };
 
-export default function(source) {
+export default function(source, xform) {
   source = slice(source);
   return source.slice(100).then(function(array) {
-    return new Shp(source, view(array));
+    return new Shp(source, view(array), xform);
   });
 };
 
-function Shp(source, header) {
+function Shp(source, header, xform) {
   var type = header.getInt32(32, true);
   if (!(type in parsers)) throw new Error("unsupported shape type: " + type);
   this._source = source;
+  this._xform = xform || function (x) { x };
   this._type = type;
   this._index = 0;
   this._parse = parsers[type];
-  this.bbox = [header.getFloat64(36, true), header.getFloat64(44, true), header.getFloat64(52, true), header.getFloat64(60, true)];
+  var topLeft = xform([header.getFloat64(36, true), header.getFloat64(44, true)]);
+  var botRight = xform([header.getFloat64(52, true), header.getFloat64(60, true)]);
+  this.bbox = [ topLeft[0], topLeft[1], botRight[0], botRight[1] ];
 }
 
 var prototype = Shp.prototype;

shp/multipoint.js

@@ -1,5 +1,7 @@
-export default function(record) {
+export default function(record, xform) {
   var i = 40, j, n = record.getInt32(36, true), coordinates = new Array(n);
-  for (j = 0; j < n; ++j, i += 16) coordinates[j] = [record.getFloat64(i, true), record.getFloat64(i + 8, true)];
+  for (j = 0; j < n; ++j, i += 16) {
+      coordinates[j] = xform([ record.getFloat64(i, true), record.getFloat64(i + 8, true) ]);
+  }
   return {type: "MultiPoint", coordinates: coordinates};
 };

shp/point.js

@@ -1,3 +1,3 @@
-export default function(record) {
-  return {type: "Point", coordinates: [record.getFloat64(4, true), record.getFloat64(12, true)]};
+export default function(record, xform) {
+  return {type: "Point", coordinates: xform([ record.getFloat64(4, true), record.getFloat64(12, true) ])};
 };

shp/polygon.js

@@ -1,7 +1,8 @@
-export default function(record) {
-  var i = 44, j, n = record.getInt32(36, true), m = record.getInt32(40, true), parts = new Array(n), points = new Array(m), polygons = [], holes = [];
+export default function(record, xform) {
+  var i = 44, j, n = record.getInt32(36, true), m = record.getInt32(40, true),
+      parts = new Array(n), points = new Array(m), polygons = [], holes = [];
   for (j = 0; j < n; ++j, i += 4) parts[j] = record.getInt32(i, true);
-  for (j = 0; j < m; ++j, i += 16) points[j] = [record.getFloat64(i, true), record.getFloat64(i + 8, true)];
+  for (j = 0; j < m; ++j, i += 16) points[j] = xform([ record.getFloat64(i, true), record.getFloat64(i + 8, true) ]);
 
   parts.forEach(function(i, j) {
     var ring = points.slice(i, parts[j + 1]);

shp/polyline.js

@@ -1,7 +1,7 @@
-export default function(record) {
+export default function(record, xform) {
   var i = 44, j, n = record.getInt32(36, true), m = record.getInt32(40, true), parts = new Array(n), points = new Array(m);
   for (j = 0; j < n; ++j, i += 4) parts[j] = record.getInt32(i, true);
-  for (j = 0; j < m; ++j, i += 16) points[j] = [record.getFloat64(i, true), record.getFloat64(i + 8, true)];
+  for (j = 0; j < m; ++j, i += 16) points[j] = xform([ record.getFloat64(i, true), record.getFloat64(i + 8, true)]);
   return n === 1
       ? {type: "LineString", coordinates: points}
       : {type: "MultiLineString", coordinates: parts.map(function(i, j) { return points.slice(i, parts[j + 1]); })};

shp/read.js

@@ -24,7 +24,7 @@ export default function() {
     function read() {
       var length = header.getInt32(4, false) * 2 - 4, type = header.getInt32(8, true);
       return length < 0 || (type && type !== that._type) ? skip() : that._source.slice(length).then(function(chunk) {
-        return {done: false, value: type ? that._parse(view(concat(array.slice(8), chunk))) : null};
+        return {done: false, value: type ? that._parse(view(concat(array.slice(8), chunk)), that._xform) : null};
       });
     }