After modifying a USB GPS receiver to use with Arduino, I continued to make a further attempt to measure distance between two locations with Arduino. The idea is straight-forward, when pressing a key, current location is stored and used as start location. The line distance of current location and the start location is calculated and displayed on the LCD on the spot. Next steps are: (1) allowing entering GPS coordinates of a location (2) calculating and displaying trip distance.
If the distance between two locations is not too long, the calculation of the line distance between them can be simplified a lot by treating the earth as flat.