I used to think that the higher GPS antenna position the better until I read the following on GPSd FAQ:
One common error is to place the GPS or antenna as high as possible. This will increase multipath effects due to signal bounce from the ground or water, which can cause the GPS to mistake its position and the time signal. The correct location for a boat GPS antenna is on the gunwale rail or pushpit rail, close to the water and as far from the mast as possible (to reduce signal bounce from the mast). If you're outside or in a fixed location, put the GPS antenna as far from buildings as possible, and on the ground.
If you're in a car, don't put the GPS antenna on the roof, put it on the towbar or some similar location. If you're driving in a heavily built up area, you're going to get signal bounce off buildings and reduced accuracy. That's just how the physics works. Note, however, that as your velocity goes up it becomes easier for the convergence filters in your GPS to spot and discard delayed signal, so multipath effects are proportionally less important in fast-moving vehicles.
Does anyone has experience placing GPS antenna on a towbar of the car as suggested? Does it give reasonable effect?
My concern is that placing antenna there will not reduce an error that much, but will expose the device (antenna) to possible mechanical damage.
So, are there any better positions apart from roof and towbar?