How to get the extent of a GeoJSON vector source?

Question

I have this GeoJSON file (polygon.geojson)...

{
  "type": "Feature",
  "geometry": { "type": "Polygon", "coordinates": [ [ [73, 15], [83.0, 15], [83, 5], [73, 5], [73, 15] ] ] },
  "properties": { "name": "Foo" }
}

...and use it as vector source:

var vectorSource = new ol.source.Vector({
    url: 'polygon.geojson',
    format: new ol.format.GeoJSON(),
    projection : 'EPSG:4326',
});

Now I want to get the extent with:

var extent = vectorSource.getExtent();

The value of extent, however, is:

Array [ Infinity, Infinity, -Infinity, -Infinity ]

I'm using OL 3.9.0 and the vector layer with this source is displayed properly. What am I doing wrong?

Principle

You could try to replace ol.js by ol-debug.js and step into the getExtent method to really see what's going on (using your browser Dev Tool). Maybe that could help. – Thralldom

Sure you don't use the useSpatialIndex or call the method before the vector source has loaded any features? – Chalaza

Maybe the data is not yet loaded when I want to calculate the extent (I noticed that the extent is set when I open the web console after the page has been loaded). How can I check if the data is ready loaded? – Principle

Answer 1

I figured it out. I need to wait until the source is loaded:

vectorSource.once('change',function(e){
    if(vectorSource.getState() === 'ready') {
        var extent = vectorSource.getExtent();
        console.log(extent);
        map.getView().fit(extent, map.getSize());
    }
});

EDIT: It might be safer to zoom only if the layer isn't empty:

vectorSource.once('change',function(e){
    if(vectorSource.getState() === 'ready') { 
        if(layers[0].getSource().getFeatures().length>0) {
            map.getView().fit(vectorSource.getExtent(), map.getSize());
        }
    }
});

Principle

Working on 3.15.1 confirmed too. – Yourself

Exactly what I was looking for and still working for openlayers 6.3.1 – Intransigent

Answer 2

If you're looking to fit to the extent try this:

var extent = *YOURLAYER*.getSource().getExtent();
map.getView().fit(extent, map.getSize());

Blastula

Yes, that's what I try to achieve. However, I get TypeError: Argument 2 of CanvasRenderingContext2D.putImageData is not a finite floating-point value. – Principle

Answer 3

You could loop for each feature and create calculate bounds like this:

var bounds = ol.extent.createEmpty();
for(var i=0;i< features.length;i++){
ol.extent.extend(bounds,features[i].getGeometry().getExtent())
}

map.getView().fitExtend(bounds , map.getSize());

Lineup