Calculate GeoJson polygon center in javascript

polygon-center-calculator.js

  function area(poly){
    var s = 0.0;
    var ring = poly.coordinates[0];
    for(i= 0; i < (ring.length-1); i++){
      s += (ring[i][0] * ring[i+1][1] - ring[i+1][0] * ring[i][1]);
    }
    return 0.5 *s;
  }

  function centroid(poly){
    var c = [0,0];
    var ring = poly.coordinates[0];
    for(i= 0; i < (ring.length-1); i++){
      c[0] += (ring[i][0] + ring[i+1][0]) * (ring[i][0]*ring[i+1][1] - ring[i+1][0]*ring[i][1]);
      c[1] += (ring[i][1] + ring[i+1][1]) * (ring[i][0]*ring[i+1][1] - ring[i+1][0]*ring[i][1]);
    }
    var a = area(poly);
    c[0] /= a *6;
    c[1] /= a*6;
    return c;
  }

//centroid(geojson.geometry);

Dude, you saved my life!

Turf.js not able to do the job with my (low quality) geoJSON file... this saved me too!

Anyone have a similar function for a multi polygon?

Anyone have a similar function for a multi polygon?

You could calc the average of the centroids like

function centroidMulti(poly) {
  if (poly?.type === 'Feature' && poly?.geometry) {
    poly = poly.geometry;
  }
  return poly.coordinates.map(centroid)
    .reduce((r, pair) => {
      r[0].push(pair[0]);
      r[1].push(pair[1]);
      return r
    }, [[], []])
    .map((a) => a.reduce(( p, c) => p + c, 0) / a.length);
}