CODEWITHSUNDEEP
javascriptjsonleafletmapboxgeojson
RKR
RKR

Reputation: 687

How to create a subset of geoJson file from existing file

I have a geoJSON file as below:

    var geoJSON=    
    {

    "type":"FeatureCollection",

    "features": [                                             
        {"type": "Feature","geometry":{"type":"LineString", "coordinates":[[102.463303,36.447488],[102.514114,36.439755]]},"properties": {"id":"01","points":9}},
        {"type": "Feature","geometry":{"type":"LineString", "coordinates":[[102.593765,36.414341],[102.634964,36.402183]]},"properties": {"id":"02","points":8}},
        {"type": "Feature","geometry":{"type":"LineString", "coordinates":[[102.880783,36.485038],[102.882156,36.561187]]},"properties":{"id":"03","points":10}}

........
and so on
                ]};

From this I want to create a variable filtered_geoJSON where only points >=9 are available like below:

var filtered_geoJSON=    
        {

    "type":"FeatureCollection",

    "features": [                                             
        {"type": "Feature","geometry":{"type":"LineString", "coordinates":[[102.463303,36.447488],[102.514114,36.439755]]},"properties": {"id":"01","points":9}},
        {"type": "Feature","geometry":{"type":"LineString", "coordinates":[[102.880783,36.485038],[102.882156,36.561187]]},"properties":{"id":"03","points":10}}

........
and so on
                ]};

Because each time I update the points of each Line String like 

  geoJSON['features'][i]['properties']['points']=data[i].points;

So from this I want to create the filtered_geoJSON variable each time and pass it to the 

L.geoJson(filtered_geoJSON, {
                     style: style,
                     onEachFeature: onEachFeature
                }).addTo(map);

So that I only draw the points which are having points >=9.

So I tried with 

var top_geoJSON={"type":"FeatureCollection","features": []};
            var c=0;
            for (i = 0; i<40000; i++) { 


                if(geoJSON['features'][i]['properties']['score']!=data[i].points){
                      links['features'][i]['properties']['score']=data[i].score;
                }

                if(geoJSON['features'][i]['properties']['points']>9){
                    filtered_geoJSON[c]=geoJSON['features'][i];
                     c++;
                }

The filtered_geoJSON is there but not plotting the lines in the map.

Any help is appreciated.

Upvotes: 1

Views: 1024

Answers (1)

ghybs
ghybs

Reputation: 53215

There is a filter option on the Leaflet L.geoJSON factory, that you can use to feed your entire geoJSON data and have Leaflet keep only the ones that meet your specified criteria (i.e. feature.properties.points >= 9 in your case).

When you re-build your filtered_geoJSON variable after updating your points, you have to build a new L.geoJSON out of it before you get something on your map.

Furthermore, even by changing the geoJSON data directly, Leaflet will not evaluate it again through the filter, so if some features go below 9, or some new ones go above, this will not be automatically reflected on the map.

The most simple solution would be to remove your previously created L.geoJSON layer group, and build a new one with your updated geoJSON data (and the same filter), so that Leaflet re-evaluates your features again.

A slightly more complex solution would be to iterate through the L.geoJSON layer group child layers directly (instead of your raw geoJSON data), typically using eachLayer, update their feature.properties.points there and determine whether it should now be hidden or shown back. You would need to create your L.geoJSON layer group initially without any filter, and manually add the child layers to the map / remove them from map. Of course you can also use an intermediate L.layerGroup.

Upvotes: 2

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