Adafruit GPS Shield + Arduino YUN

Hi ,

I purchased an adafruit GPS shield with Arduino YUN for measuring the Longtitude , latitude and Altitude. I want to get these numbers on my phone by wifi.
I had some more problem so you can check it on adafruit website:
Adafruit Forum

Now the problem is Altitude. I used Drone in my project so when Drone is on the ground , Altitude is about 185 to 190… but when drone is in sky the Altitude doesn’t change as fast as other data and also never show me the correct altitude. I want to know is it the GPS problem or YUN ???