Some users would like to use UART1 or Serial1 while compiling with GNSS library. This tutorial shows how to do this. It is assumed that user is familiar with the concepts in this “Hello World” tutorial:
http://www.navspark.com.tw/blog/tutorial-hello-world
To turn off NMEA output sentence, set message interval to 0 as below. GNSS.cpp is under /Arduino-1.5.6-r2-Bin-NavSpark/hardware/Arduino/leon/cores/Arduino