¿Cómo se puede leer el archivo GeoJSON externo de las capas abiertas?

Question

Tengo que dibujar algunas líneas con OpenLayers. Las características de la línea están codificadas como formato GeoJSON. Mi código está bien para las características de GeoJSON codificadas. Pero, si pongo estas características en un archivo separado e intento cargarlo. Simplemente no funciona. No sé cuál es el problema con la carga de un archivo GeoJSON externo. He dado tanto el código.

Código 1:

// This code is ok with hard coded GeoJSON features 
map.addControl(new OpenLayers.Control.LayerSwitcher()); 

      vectorLayer = new OpenLayers.Layer.Vector("Lines"); 

      var myGeoJSON = { "type": "FeatureCollection", 
       "features": 
       [ 

        { "type": "Feature", "properties": { "LENGTH": 756.304000}, "geometry": { "type": "LineString", "coordinates": [ [ 18.105018, 59.231027 ], [ 18.104176, 59.230737 ], [ 18.103928, 59.230415 ], [ 18.103650, 59.230336 ], [ 18.103028, 59.230463 ], [ 18.102491, 59.230418 ], [ 18.101976, 59.230237 ], [ 18.100893, 59.230110 ], [ 18.100117, 59.230016 ], [ 18.097715, 59.230262 ], [ 18.096907, 59.230376 ], [ 18.096637, 59.230405 ], [ 18.096578, 59.230428 ], [ 18.096429, 59.230450 ], [ 18.096336, 59.230479 ], [ 18.096108, 59.230534 ], [ 18.095971, 59.230600 ], [ 18.095925, 59.230633 ], [ 18.095891, 59.230665 ], [ 18.094000, 59.231676 ], [ 18.093864, 59.231720 ] ] } } 
        ,     
      { "type": "Feature", "properties": { "LENGTH": 1462.390000}, "geometry": { "type": "LineString", "coordinates": [ [ 17.877073, 59.461653 ], [ 17.877116, 59.461598 ], [ 17.876936, 59.461507 ], [ 17.876936, 59.461323 ], [ 17.876773, 59.461098 ], [ 17.876430, 59.460885 ], [ 17.876413, 59.460553 ], [ 17.876576, 59.460280 ], [ 17.876575, 59.460078 ], [ 17.876762, 59.460060 ], [ 17.877371, 59.460042 ], [ 17.877808, 59.460046 ], [ 17.878641, 59.460046 ], [ 17.879010, 59.460078 ], [ 17.879337, 59.460044 ], [ 17.879526, 59.459878 ], [ 17.879749, 59.459563 ], [ 17.880058, 59.459538 ], [ 17.880435, 59.459503 ], [ 17.887550, 59.453608 ], [ 17.887696, 59.453430 ], [ 17.887971, 59.453150 ], [ 17.888221, 59.452843 ], [ 17.888246, 59.452721 ], [ 17.888435, 59.452609 ], [ 17.888470, 59.452568 ], [ 17.888517, 59.452410 ] ] } } 

       ] 
      }; 

      var geojson_format = new OpenLayers.Format.GeoJSON({ 
       'internalProjection': map.baseLayer.projection, 
       'externalProjection': new OpenLayers.Projection("EPSG:4326") 
      }); 


      map.addLayer(vectorLayer); 

      vectorLayer.addFeatures(geojson_format.read(myGeoJSON)); 

      map.setCenter(
       new OpenLayers.LonLat(18.068611, 59.329444).transform(
        new OpenLayers.Projection("EPSG:4326"), 
        map.getProjectionObject() 
       ), 10 
      ); 

Código 2: Este código muestra un error que no se pudo cargar características

//This code does not work because it can not load the external GeoJSON file 

map.addControl(new OpenLayers.Control.LayerSwitcher()); 

vectorLayer = new OpenLayers.Layer.Vector("Lines"); 

var myGeoJSON = new OpenLayers.Layer.Vector("Lines", { 
    strategies: [new OpenLayers.Strategy.Fixed()],     
    protocol: new OpenLayers.Protocol.HTTP({ 
      url: "ml/lines.json" 

      }) 
    }); 

var geojson_format = new OpenLayers.Format.GeoJSON({ 
    'internalProjection': map.baseLayer.projection, 
    'externalProjection': new OpenLayers.Projection("EPSG:4326") 
    }); 

map.addLayer(vectorLayer); 

vectorLayer.addFeatures(geojson_format.read(myGeoJSON)); 

map.setCenter(
    new OpenLayers.LonLat(18.068611, 59.329444).transform(
     new OpenLayers.Projection("EPSG:4326"), 
      map.getProjectionObject() 
       ), 10 
      ); 

Gracias de antemano

Answer 1

geojson_layer = new OpenLayers.Layer.Vector("GeoJSON", { 
      strategies: [new OpenLayers.Strategy.Fixed()], 
      protocol: new OpenLayers.Protocol.HTTP({ 
       url: "ml/lines.json", 
       format: new OpenLayers.Format.GeoJSON() 
      }) 
     }); 

Ver mi pequeño example.