I used the GPS Portable Car Navigation System, "Mini Gorilla". The model was NV-SB250DT
and made by SANYO.
And now, I use Model : NV-SB540DT. This model has 8GB SSD, Digital TV Tuner, MP3 player, battery, 5.2 V type wide TFT screen and real-time traffic information system (VICS: vehicle information and communication system).
And also, it has gyro sensors for estimating height and horizontal movement direction and a acceleration sensor for measuring driving distance and speed.