How can obtain geojson geometry ? OL3

Question

I need to get a GeoJSON geometry of this, then use a buffer for the TURF library.

Get get data from GeoJSON turf but would not admit it in any way. any ideas ?

This is my code:

var feature_buff = select2.getFeatures();
var geojson  = new ol.format.GeoJSON();

for (var i=0;i<feature_buff.getLength();i++){
json.push(geojson.writeFeature(feature_buff.item(i)));
var obj =geojson.writeFeatures(feature_buff.item(i))

var geom = geojson.readGeometry(obj);


var buffer = turf.buffer(geom, 2000, 'kilometers')

this code fail. and this is the error:

Uncaught TypeError: (0 , ls[b.type]) is not a function

Answer 1

You don't provide the "right" content to Turf (your geom is not the expected content for Turf)

feats = select2.getFeatures();

var geojson  = new ol.format.GeoJSON();

as_geojson = geojson.writeFeatures(feats, {
  featureProjection: 'EPSG:3857',
  dataProjection: 'EPSG:4326'
});

turf.buffer(as_geojson, 20, 'kilometers');

You can also see this demo I've made months ago and this other official one.

If you don't use extensively Turf, it's also possible to use JSTS (JavaScript Topology Suite), a library to manipulate geometry in JavaScript. A demo with buffer is available at the official website.

Answer 2

This is the solution :

select2 = new ol.interaction.Select({
        condition: ol.events.condition.click
    });

map.addInteraction(select2);
//var feature_buff = select2.getFeatures();
select2.getFeatures().on('change:length', function(e){   

var feature_buff = select2.getFeatures();

var geojson  = new ol.format.GeoJSON();



for (var i=0;i<feature_buff.getLength();i++){
    json.push(geojson.writeFeature(feature_buff.item(i)));

    prueba.getSource().addFeature(geojson.readFeature(json[json.length-1]) );
    polys_fc=JSON.parse(json[json.length-1]);
    console.log(polys_fc);
    prueba.getSource().addFeatures(geojsonToFeatures(polys_fc, {
      featureProjection: 'EPSG:3857'
    }));

    var buffer = turf.buffer(polys_fc, 50000, 'kilometers');
    buffer.properties = {
    "fill": "#6BC65F",
    "stroke": "#25561F",
    "stroke-width": 2
    };
    console.log(buffer);

    prueba.getSource().addFeatures(geojsonToFeatures(buffer));





}  });

But now i have other question, the distance buffer don't work well but i don't know where is the problem.