Create GeoJSON in php

GeoJSON is a text format for encoding various geographical structures. I have a large number of point data with various extra information stored in a postgresql data base. I fetch all the data into an array in php, using PDO::FETCH_ASSOC, that is each row that has been fetched is an item in a numerical array, for each row, the various fields are coded as an associative array, so I have a structure like

Array
(
    [0] => Array
        (
            [id] => 210
            [name] => Sellafield
            [lat] => 54.43
            [lon] => -3.52
            [type] => Reprocessing plant
            [country] => Great Britain
        )

    [1] => Array
        (
            [id] => 177
            [name] => Dounreay
            [lat] => 58.57
            [lon] => -3.73
            [type] => Reprocessing plant
            [country] => Great Britain
        )
)

Now I want to use the lat and lon field to create the coordinate fields in GeoJSON and store the rest of the information as properties. Having the dataset stored as $dataset, I run the following code

$minlat=100;
$maxlat=-100;
$minlon=400;
$maxlon=-200;
foreach($dataset as &$item){ # Uses a pointer to refer to $item, so that changes are reflected in $dataset
   $item['geometry']['type']='Point';
   # Must make sure the coordinates are stored as numbers, not strings      
   $lon=$item['lon']*1;
   $lat=$item['lat']*1;
   $item['geometry']['coordinates']=array($lon,$lat);
   $minlon=min($minlon,$lon);                                                                                    
   $maxlon=max($maxlon,$lon);                                                                                    
   $minlat=min($minlat,$lat);                                                                                    
   $maxlat=max($maxlat,$lat);                                                                                    
   unset($item['lat']);
   unset($item['lon']);
   foreach($item as $k=>$v){  
      # Don't want to mess with geometry as it is already set
      # Id should also be set directly.
      if(!($k='geometry' || $k=='id')) {
         # Must make sure that numeric values are correctly handled
         if(is_numeric($v)?$v*1:$v;
         $props[$k]=$v;
         unset($item[$k]);
      }
    }                                                                                                      
    $item['type']='Feature';                                                                          
    $item['properties']=$props;
  }
  $dataset=array("type"=>"FeatureCollection","features"=>$dataset);
  $dataset['bbox']=array($minlon,$minlat,$maxlon,$maxlat);
  # Defining crs for WGS84 lat/lon
  $dataset['crs']=array("type"=>"name","properties"=>array("name","urn:ogc:def:crs:EPSG::4326"));  
$json=json_encode($dataset);