Can't implement NMEA example in another class

[MauriceChocoSwiss]

Hi, i try to get a simple data location, the example NMEASimple work fine, i get position. But when i wan't to use in an another class than .ino file and call in in the main loop, it didn't work. I use AltSoftSerial to connect to my GPS.

Here is my code

GPS.h

#include <AltSoftSerial.h>

class GPS{
public:
    GPS();
    void GetGPSData();
    void gpsBegin();
private:
    AltSoftSerial gpsSerial;
};

GPS.cpp

GPS::GPS() : gpsSerial(52, 53)
{

}

void GPS::gpsBegin()
{
    gpsSerial.begin(9600);
}

void GPS::GetGPSData()
{
    while (gps.available(gpsSerial)) {

            fix = gps.read();

            Serial.print("Gps en vue : ");
            Serial.print(fix.satellites);
            Serial.print(F("Location: "));
            if (fix.valid.location) {
                Serial.print(fix.latitude(), 6);
                Serial.print(',');
                Serial.print(fix.longitude(), 6);
            }

            Serial.print(F(", Altitude: "));
            if (fix.valid.altitude)
                Serial.print(fix.altitude());

            Serial.println();
    }
}

Main file is to long but i'll simplify here

#include "GPS.h"
...

GPS gpsData;

void setup()
{
    Serial.begin(9600);
    gpsData.gpsBegin();

}

void loop()
{
        gpsData.GetGPSData();
}

Like i say, the code in GPS.cpp work fine if i put it in the main loop... I try to check if gpsSerial is available before read, it work, but no gps informations...

Thank you for your help