map - ¿Cómo leer un archivo GeoJSON externo desde openlayers?

Question

Tengo que dibujar algunas líneas por OpenLayers. Las características de la línea están codificadas como formato GeoJSON. Mi código está bien para las funciones codificadas de GeoJSON. Pero, si pongo estas características en un archivo separado y trato de 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 indica que no pudo cargar funciones

//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 por adelantado

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()
            })
        });

Mira mi pequeño example .