Remove null attributes from GeoJSON

Question

I used the following command to reproject a GeoJSON from lat/lon to 3857:

ogr2ogr -f "GeoJSON" results_3857.json -t_srs "EPSG:3857" results.json

Unexpectedly, the resulting file was 5 times larger than the original.

Turns out the resulting file contains all properties for each feature, while the original contained only those properties that were not null.

For example the original might have had a properties objects that look like this:

..."properties": { a: 1, d: 2, f: 1 }....
..."properties": { b: 1, c: 2, d: 2 }...

while the newly reprojected file has converted them to look like this:

..."properties": { a: 1, b: null, c: null, d: 2, e: null, f: 1 }...
..."properties": { a: null, b: 1, c: 2, d: 2, e: null, f: null }...

I don't want these extra null entries in my reprojected GeoJSON.

And so my question is this:

How can I remove those properties that have null values from the GeoJSON?

Is there some flag I can use in the ogr2ogr command?
Maybe there is a subsequent gdal command I can use to remove those attributes that have a null value?

Answer 1

for a GeoJSON featureCollection, you could do something like this:

var myGeoJSON = {
  "type": "FeatureCollection",
  "features": [
    {
      "type": "Feature",
      "properties": {
        "name": "hi",
        "num": 9,
        "other": null
      },
      "geometry": {
        "type": "Point",
        "coordinates": [
          23.203125,
          53.12040528310657
        ]
      }
    }
    //,....
  ]
}

for(var i=0; i<myGeoJSON.features.length; i++){
    var obj = myGeoJSON.features[i].properties;
    for(var key in obj){
        var attrName = key;
        var attrValue = obj[key];
        if (!attrValue){
          delete obj[key];
        }
    }
}

i posted a sample here