How to specify the projection for GeoJSON in openlayers3?

问题

My intention is to load GeoJSON data and display it on the map. Coordinates of the features specified in GeoJSON are normal lon/lat. For some reason openlayers is rendering them using the projection used by the map and without converting them.

// Underlying sat layer.
var world = new ol.layer.Tile({
    source: new ol.source.MapQuest({layer: 'sat'})
});

// GeoJSON data.
var geojsonObject = {
    'type': 'FeatureCollection',
    'features': [
        {
            'type': 'Feature',
            'geometry': {
                'coordinates': [ 50.07539747, 19.76809501 ], 
                'type': 'Point'
            },
        }
    ]
};

var vectorSource = new ol.source.Vector({
    features: (new ol.format.GeoJSON()).readFeatures(geojsonObject)
});

var vectorLayer = new ol.layer.Vector({
    source: vectorSource
});

// Map.
map = new ol.Map({
    target: 'map',
    layers: [world, vectorLayer],
    view: new ol.View({
        center: ol.proj.transform([37.41, 8.82], 'EPSG:4326', 'EPSG:3857'),
        zoom: 2
    })
});

The point is being rendered in the middle of the map. By placing multiple points I determined that they are in fact moved relative to each other but by a small amount which leads me to believe the for some reason the map uses a different coordinate system for them.

What I tried: Setting crs in GeoJSON, providing defaultDataProjection option to format. I use openlayers v3.8.2 and all solutions I found online are very outdated (and as far as I can see the API used to be way better, maybe I should just switch to an old version).

回答1:

Just use a featureProjection to read features like:

var vectorSource = new ol.source.Vector({
    features: new ol.format.GeoJSON().readFeatures(geojsonObject,{
        featureProjection: 'EPSG:3857'
    })
});

UPDATE: When reading features from url is even easier, OL makes the conversion internally for you:

var geojson_layer = new ol.layer.Vector({
    source: new ol.source.Vector({
        url: 'file.geojson',
        format: new ol.format.GeoJSON()
    })
});

Demo - http://plnkr.co/edit/GvdVNE?p=preview

来源：https://stackoverflow.com/questions/32455040/how-to-specify-the-projection-for-geojson-in-openlayers3

标签

javascript

openlayers-3