function Gethotspots( $$db, value ) {
  /* Create the SQL query to retrieve POIs within the “radius” returned from
  GetPOI request. Returned POIs are sorted by distance and the first 50 POIs
  are selected. The distance is caculated based on the Haversine formula.
  Note: this way of calculation is not scalable for querying large database.
  */
  // “:lat1”, “:lat2”, “:long” and “:radius” are named parameter markers for
  // which real values will be substituted when the statement is executed.
  // $$sql is returned as a PDO statement object.
          sql = $$db->prepare( “
                  SELECT id,
                  attribution,
                  title,
                  lat,
                  lon,
                  imageURL,
                  line4,
                  line3,
                  line2,
                  type,
                  dimension,
                  (((acos(sin((:lat1 * pi() / 180)) * sin((lat * pi() / 180)) +
                  cos((:lat2 * pi() / 180)) * cos((lat * pi() / 180)) *
                  cos((:long - lon) * pi() / 180))
                  ) * 180 / pi()) * 60 * 1.1515 * 1.609344 * 1000) as distance
                  FROM POI_Table
                  HAVING distance < :radius
                  ORDER BY distance ASC
                  LIMIT 0, 50 ” );
  
          // PDOStatement::bindParam() binds the named parameter markers to the
          // specified parameter values.
          sql->bindParam( ’:lat1’, $$value[’lat’], PDO::PARAM_STR );
          sql->bindParam( ’:lat2’, $$value[’lat’], PDO::PARAM_STR );
          sql->bindParam( ’:long’, $$value[’lon’], PDO::PARAM_STR );
          sql->bindParam( ’:radius’, $$value[’radius’], PDO::PARAM_INT );
  
          // Use PDO::execute() to execute the prepared statement sql.
          $$sql->execute();
          
          // Iterator for the response array.
          i = 0;
  
          // Use fetchAll to return an array containing all of the remaining rows
          // in the result set.
          // Use PDO::FETCH_ASSOC to fetch $$sql query results and return each row
          // as an array indexed by column name.
          pois = $$sql->fetchAll(PDO::FETCH_ASSOC);
  
          /* Process the pois result */        
          // if $$pois array is empty, return empty array.
          if ( empty(pois) ) {
                  $$response[”hotspots”] = array ();
          }//if
          else {
          
                  // Put each POI information into response[“hotspots”] array.
                  foreach ( $$pois as poi ) {
  
                  // If not used, return an empty actions array.
                          $$poi[“actions”] = array();
                          
                          // Store the integer value of “lat” and “lon” using predefined function
                          // ChangetoIntLoc.
                          poi[“lat”] = ChangetoIntLoc( $$poi[“lat”] );
                          poi[“lon”] = ChangetoIntLoc( $$poi[“lon”] );
  
                          // Change to Int with function ChangetoInt.
                          poi[“type”] = ChangetoInt( $$poi[“type”] );
                          poi[“dimension”] = ChangetoInt( $$poi[“dimension”] );
  
                          // Change to demical value with function ChangetoFloat
                          poi[“distance”] = ChangetoFloat( $$poi[“distance”] );
                  
                          // Put the poi into the response array.
                          response[“hotspots”][$$i] = poi;
                          $$i++;
                  }//foreach
          }//else
          return response[“hotspots”];
  }//Gethotspots
  
  // Convert a decimal GPS latitude or longitude value to an integer by
  // multiplying by 1000000.
  //
  // Arguments:
  // value_Dec ; The decimal latitude or longitude GPS value.
  //
  // Returns:
  // int ; The integer value of the latitude or longitude.
  //
  function ChangetoIntLoc( $$value_Dec ) {
          return value_Dec * 1000000;
  }//ChangetoIntLoc
  
  // Change a string value to integer.
  //
  // Arguments:
  // string ; A string value.
  //
  // Returns:
  // Int ; If the string is empty, return NULL.
  //
  function ChangetoInt( $$string ) {
          if ( strlen( trim( string ) ) != 0 ) {
                  return (int)$$string;
          }
          else
                  return NULL;
  }//ChangetoInt
  
  // Change a value to float
  //
  // Arguments:
  // string ; A string value.
  //
  // Returns:
  // float ; If the string is empty, return NULL.
  //
  function ChangetoFloat( string ) {
          if ( strlen( trim( $$string ) ) != 0 ) {
          return (float)string;
          }
          else
                  return NULL;
          }//ChangetoFloat
  
          // Put the JSON representation of $$response into jsonresponse.
          $$jsonresponse = json_encode( response );
          
          // Declare the correct content type in HTTP response header.
          header( “Content-type: application/json; charset=utf-8” );
          
          // Print out Json response.
          echo $$jsonresponse;
          
          /* Close the MySQL connection.*/
          // Set db to NULL to close the database connection.
          $$db=null;
  ?>