How to print (or store) gps lat, lng value (TinyGPS++) with Bluetooth BLE nRF8001?
The Arduino Stream/Print classes may sometime need some extra attention.

BTLEserial.println(gps.location.lat()`, 6); 


The member function is available in the class Print but gets "hidden". You can help the compiler to find it with a prefix:

BTLEserial.Print::println(gps.location.lat()`, 6); 


Cheers!