Using GPS to record actual path taken?

What you require is already available. Visit your closest hardware supplier and find out what is available. Then check the web for alternatives.

"instantaneous curvatures of that path" - The level of accuracy may be insufficient but it can be overcome.

Your final purpose is not clear and therefore the following might not be applicable.

We made a instrument to measure the driving style of fleet drivers. We measured the acceleration, braking, cornering, speed etc. The driver could then later be evaluated and warned of unacceptable behaviour.

Thank you for your response.

To clarify a bit: application = data acquistion to record vehicle dynamics. Am hoping to attain accuracy better than 1 meter. Sample rate at ~20-50 Hz seems proper.

Desire to relate other variables to vehicle position, and to calculations made from several measurement points.

Initial testing would be in North America.

Since my 1st post, i've been looking at the GALILEO system, & it promises higher precision than GPS. Will it also be available worldwise? Have also heard rumors that its accuracy would be downgraded for military reasons.

A lot depends on where you are trying to use the service and whjat kind of hardware you are using. Here in the US there are literally dozens of providers doing this in various ways, AirClic, Xora, Agilis, to name a few. They can work with GPS devices or cell phones/modules in most cases.

While I don't know all of them, my good friend, Mr. Google does.

Is there a GPS that can save the actual path taken on a small memory card? When driving to a remote area that is not on the map it would be handy if the GPS could save the actual path taken. This can be used for going to the same location next time. The GPS should be able to provide driving directions using the memory card as a reference. It can also be used to prevent the GPS from giving confusing driving directions. My NAVMAN is giving confusing driving directions when driving in the Houston area.

Well, it all depends on the app you are using. In and of itself, GPS doesn't give directions. GPS is getting data from a satellite and computing location. This information is passed to another application which is tied to some sort of geo-data base. It is the application that decides what directions to give you based on the start and end points and what the app thinks is in between.

The big issue with any sort of computer based directions is that it doesn't always have the same local knowledge that you have. Get a map of a city you are not familiar with, then figure out how to get from the airport (for example) to a hotel in the downtown area. Then go see what Mapquest says is the best route. Or maybe do something similar with a part of Houston that you are not familiar with. The you could go test. I bet you find that the directions are basically OK, but there may be some quirks that "local knowledge" would overcome.