[untrained skeptic]

If your car does have a film on the windows that is interfering with the GPS you can either mount an external antenna, or if you still get good cell phone reception you could possibly use the "GPS" service from a cell phone provider.

The cell phones are actually calculating their distance from various towers rather than using satellite signals directly, so if the frequencies the cell phones use don't have trouble with the film, it won't matter that the film blocks the satellite signals.

There are also places where a cell phone GPS will work where a real GPS receiver will not and vice versa. The cell phone ones may still work indoors or in a city with tall buildings where you can't get line of sight to the satellites. However, in rural areas where cell service is hit and miss, the satellite is your best choice.

[MindBender26]

Real GPS is accurate to 33 feet lat/lon and 16 feet vertical. How accurate is the cell phone pseudo-GPS?