[UPDATED] Help Hacking a GPS module named VK16HX

Hi, I have problem with this script. It work chaotical. I want to know there offset of GPS coordinate. Interupts? Synchronization? Any idea??? Thanks

#include <SoftwareSerial.h>
#include <TinyGPS++.h>

#define RXPIN 3
#define TXPIN 2

float latitude1,longitude1,latitude2,longitude2,of_lat,of_lon;

SoftwareSerial gpsSerial(RXPIN, TXPIN); // create gps sensor connection
TinyGPSPlus gps; // create gps object

void setup(){
 Serial.begin(115200); // connect Serial
 gpsSerial.begin(9600); // connect gps sensor
}

void loop(){
 
 while(gpsSerial.available() > 0) // check for gps data
 gps.encode(gpsSerial.read()); // encode gps data
 if (gps.location.isUpdated())
 {
   // display position

   latitude1 = gps.location.lat();
   longitude1 = gps.location.lng();
   Serial.print("LAT=");  Serial.println(latitude1,5);
   Serial.print("LONG="); Serial.println(longitude1,5);
   Serial.println("This is first data from GPS");
   Serial.println("");
   delay(10000);
 }

 while(gpsSerial.available() > 0) // check for gps data
 gps.encode(gpsSerial.read()); // encode gps data
 if (gps.location.isUpdated())
 {
   // display position

   latitude2 = gps.location.lat();
   longitude2 = gps.location.lng();
   Serial.print("LAT=");  Serial.println(latitude2,5);
   Serial.print("LONG="); Serial.println(longitude2,5);
   Serial.println("This is second data from GPS");
   Serial.println("");
   delay(2000);

   of_lat = latitude2-latitude1;
   of_lon = longitude2-longitude1;
   Serial.print("Offset Latitude=");  Serial.println(of_lat,5);
   Serial.print("Offset Longtitude="); Serial.println(of_lon,5);
   Serial.println("");
   Serial.println("");
   delay(8000);

 }

}