refactor parser, improve centroid func, add fixture

src/wrap.js

@@ -0,0 +1,44 @@
+
+/**
+  normalize co-ordinates that lie outside of the normal ranges.
+
+  longitude wrapping simply requires adding +- 360 to the value until it comes
+  in to range.
+
+  for the latitude values we need to flip the longitude whenever the latitude
+  crosses a pole.
+**/
+
+
+function wrap( lat, lon ){
+
+  var point = { lat: lat, lon: lon };
+  var quadrant = Math.floor( Math.abs(lat) / 90) % 4;
+  var pole = ( lat > 0 ) ? 90 : -90;
+  var offset = lat % 90;
+
+  switch( quadrant ){
+    case 0:
+      point.lat = offset;
+      break;
+    case 1:
+      point.lat = pole - offset;
+      point.lon += 180;
+      break;
+    case 2:
+      point.lat = -offset;
+      point.lon += 180;
+      break;
+    case 3:
+      point.lat = -pole + offset;
+      break;
+  }
+
+  if( point.lon > 180 || point.lon <= -180 ){
+    point.lon -= Math.floor(( point.lon + 180 ) / 360) * 360;
+  }
+
+  return point;
+}
+
+module.exports = wrap;

stream/centroid.js

@@ -5,15 +5,15 @@ var through = require('through2'),
 
 // https://github.com/turf-junkyard/turf-along
 // https://github.com/turf-junkyard/turf-line-distance
-var UNIT = 'km';
+var UNIT = 'kilometers';
 
 function centroid(){
   return through.obj( function( geojson, _, next ){
     try {
 
-      // total distance in km
+      // total distance in meters
       var dist = distance( geojson, UNIT );
-      geojson.properties.distance = dist;
+      geojson.properties.distance = (dist * 1000).toFixed(4);
 
       // interpolate middle of path
       var point = along( geojson, dist/2, UNIT );

stream/decode.js

@@ -2,12 +2,14 @@
 var split = require('split'),
     through = require('through2'),
     parser = require('./parser'),
+    unwrap = require('./unwrap'),
     centroid = require('./centroid');
 
 function decode( streamIn, streamOut ){
   return streamIn
     .pipe( split() )
-    .pipe( parser() )
+    .pipe( parser( 6 ) )
+    .pipe( unwrap() )
     .pipe( centroid() )
     .pipe( through.obj( function( obj, _, next ){
       next( null, JSON.stringify( obj, null, 2 ) );

stream/parser.js

@@ -2,21 +2,49 @@
 var through = require('through2'),
     polyline = require('polyline');
 
-function parser(){
+/**
+  note: you must select the same 'precision' value that was used when encoding
+  the polyline.
+
+  valhalla: 6
+  osrm: 5
+
+  parser expects data to be:
+   - newline terminated with \n
+   - column delimited with \0
+   - in the format: {encoded_polyline}\0{name1}\0{name2}...\n
+**/
+function parser( precision ){
   return through.obj( function( row, _, next ){
     var cols = row.split('\0');
     try {
-      var names = cols.slice(1);
-      if( names.length ){
-        var geojson = polyline.toGeoJSON(cols[0]);
-        geojson.properties = { name: names[0] };
+      // must contain a polyline and at least one name
+      if( cols.length > 1 ){
+
+        // decode polyline
+        var geojson = polyline.toGeoJSON(cols[0], precision);
+
+        // select name
+        geojson.properties = { name: selectName(cols.slice(1)) };
+
         this.push( geojson );
       }
     } catch( e ){
       console.error( 'polyline parsing error', e );
     }
+
     next();
   });
 }
 
+// each connected road can have one or more names
+// we select one name to be the default.
+function selectName( names ){
+  // return the longest name
+  // @todo: can we improve this logic?
+  return names.reduce( function( a, b ){
+    return a.length > b.length ? a : b;
+  });
+}
+
 module.exports = parser;

stream/unwrap.js

@@ -0,0 +1,25 @@
+
+var through = require('through2'),
+    wrap = require('../src/wrap');
+
+function unwrap(){
+  return through.obj( function( geojson, _, next ){
+    try {
+
+      // unwrap coordinates which go around the globe
+      geojson.coordinates = geojson.coordinates.map( function( coord ){
+        var w = wrap( coord[1], coord[0] );
+        return [ w.lon, w.lat ];
+      });
+
+      this.push( geojson );
+
+    } catch( e ){
+      console.error( 'polyline unwrap error', e );
+    }
+
+    next();
+  });
+}
+
+module.exports = unwrap;