OpenLayers GeoJSON – How to Style Circle Radius Based on GeoJSON Property in OpenLayers 3

geojsonopenlayers

I want to represent the weight of each point of my geojson collection by a circle with a scalable radius.

Here an sample of my GeoJSON file:

"features": [
{ "type": "Feature", "properties": { "id": 20401, "radius": 0.032878 }, "geometry": { "type": "Point", "coordinates": [ 6.569957243078316, 46.744609055776721 ] } },
{ "type": "Feature", "properties": { "id": 20402, "radius": 0.024677 }, "geometry": { "type": "Point", "coordinates": [ 6.56996417375066, 46.744609055776721 ] } },

Is there a way to extract the radius property?

actually I represent my points like this

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

It's the default representation who appear on the map.

Best Answer

Like @bartvde pointed out you can use an ol.StyleFunction() (see API):

var points = new ol.layer.Vector({
    source: new ol.source.Vector({
        // ...
        style: function(feature, viewResolution){
            // access your radius property
            var r = feature.get('radius');
            // create your style...
            var style = new ol.style.Style({
                // ...
                image: new ol.style.Circle({
                    // ...
                    radius: r
                })
            });
            return style;
        }
    })
});

Related Solutions

[GIS] Selecting feature programmatically from GeoJSON using OpenLayers

You could use the method "getFeaturesByAttribute"

or iterate through all features:

 for(var i = 0; i < yourgeojsonlayer.features.length; i++) { 
    if(yourgeojsonlayer.features[i].attributes.searchedAttribute == 'searchedValue')
     { selectFeatureControl.select(yourgeojsonlayer.features[i]); break; } 
    }

Ps: makes necessary to create a select control first and assign the variable name you use in the for loop (here selectFeatureControl)

I just wrote down a quick example here: http://jsfiddle.net/expedio/sh9wv4m7/

PostGIS GeoJSON – Storing GeoJSON FeatureCollection in PostgreSQL

Assuming you have at least PostgreSQL version 9.3, you can use a few JSON functions and operators to extract the relevant parts of the GeoJSON specification required by ST_GeomFromGeoJSON to create geometries.

Try the following, where you can replace the JSON in the top part:

WITH data AS (SELECT '{ "type": "FeatureCollection",
    "features": [
      { "type": "Feature",
        "geometry": {"type": "Point", "coordinates": [102.0, 0.5]},
        "properties": {"prop0": "value0"}
        },
      { "type": "Feature",
        "geometry": {
          "type": "LineString",
          "coordinates": [
            [102.0, 0.0], [103.0, 1.0], [104.0, 0.0], [105.0, 1.0]
            ]
          },
        "properties": {
          "prop0": "value0",
          "prop1": 0.0
          }
        },
      { "type": "Feature",
         "geometry": {
           "type": "Polygon",
           "coordinates": [
             [ [100.0, 0.0], [101.0, 0.0], [101.0, 1.0],
               [100.0, 1.0], [100.0, 0.0] ]
             ]
         },
         "properties": {
           "prop0": "value0",
           "prop1": {"this": "that"}
           }
         }
       ]
     }'::json AS fc)

SELECT
  row_number() OVER () AS gid,
  ST_AsText(ST_GeomFromGeoJSON(feat->>'geometry')) AS geom,
  feat->'properties' AS properties
FROM (
  SELECT json_array_elements(fc->'features') AS feat
  FROM data
) AS f;

Finds three geometries. The geom column has the geometry object, and the gid is the feature number. The ST_AsText function shows the WKT equivalent of each geometry. I've also included the properties or attributes that can be defined for each geometry, as is shown in the specification.

 gid |                   geom                   |              properties
-----+------------------------------------------+--------------------------------------
   1 | POINT(102 0.5)                           | {"prop0": "value0"}
   2 | LINESTRING(102 0,103 1,104 0,105 1)      | {                                   +
     |                                          |           "prop0": "value0",        +
     |                                          |           "prop1": 0.0              +
     |                                          |           }
   3 | POLYGON((100 0,101 0,101 1,100 1,100 0)) | {                                   +
     |                                          |            "prop0": "value0",       +
     |                                          |            "prop1": {"this": "that"}+
     |                                          |            }
(3 rows)

You should assign an SRID for the geometry, using ST_SetSRID.

Or if you simply need a single heterogeneous GEOMETRYCOLLECTION, you can make it compact like this:

SELECT ST_AsText(ST_Collect(ST_GeomFromGeoJSON(feat->>'geometry')))
FROM (
  SELECT json_array_elements('{ ... put JSON here ... }'::json->'features') AS feat
) AS f;

GEOMETRYCOLLECTION(POINT(2565453.18267219 -3835048.65976031),LINESTRING(2727584.72197102 -3713449.19424187,2732476.69178127 -3992291.47342619),POLYGON((2442627.90254053 -3705499.95430853,2425506.00820465 -3886502.83728783,2555143.20817631 -3910962.68633909,2442627.90254053 -3705499.95430853)))

See also Creating GeoJSON Feature Collections with JSON and PostGIS functions from the Postgres OnLine Journal, which does the opposite.

Best Answer

Related Solutions

[GIS] Selecting feature programmatically from GeoJSON using OpenLayers

PostGIS GeoJSON – Storing GeoJSON FeatureCollection in PostgreSQL

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