text: export function distance(lon1, lat1, lon2, lat2) {
  	if ((lat1 === lat2) && (lon1 === lon2)) {
  		return 0;
  	}
  	else {
  		var radlat1 = Math.PI * lat1 / 180;
  		var radlat2 = Math.PI * lat2 / 180;
  		var theta = lon1 - lon2;
  		var radtheta = Math.PI * theta / 180;
  		var dist = Math.sin(radlat1) * Math.sin(radlat2) + Math.cos(radlat1) * Math.cos(radlat2) * Math.cos(radtheta);
  		if (dist > 1) {
  			dist = 1;
  		}
  		dist = Math.acos(dist);
  		dist = dist * 180 / Math.PI;
  		dist = dist * 60 * 1.1515;
  		return dist;
  	}
  }