GPS Project

I would like to have your help and thought in my project. Basically, my project is to control two D.C. motors, attached to a boat, using Arduino and GPS. My project is similar to your project, Pathfinder. Let me explain to you my project. I am going to use the coordinates where the boat is turned on as a fix coordinates or the center. Then, the boat would move in random motion. Once the boat be far from the fix coordinates or the center 20 meters, the boat return to the fix coordinates. Therefore, my range is 20 meters radius from the fix coordinates or the center. I think to use the GPS to detect the fix coordinates position and save it as a reference point. Then, the GPS will track how far the boat is from the fix point. Therefore, the Arduino will first save the reference point, then, the Arduino will compare the current position received from the GPS with the reference point to control the motors to ensure the boat is within 20 meters radius. My project is like this video. Finally, all the data should be erase once the boat is turn off. The second video shows how the two motor will utilize.

http://www.youtube.com/watch?v=VSub2p-j6V8

http://www.youtube.com/watch?v=0Nt2ElVCjC0

It has been said that typical civilian GPS is only accurate to ~30 feet. Is this what you expect?

That is about the average error at any moment. Over a period of an hour you can average to get more accuracy. Unfortunately that doesn't work for a moving object. Anyone want code? It tells you the estimated error as it is sampling.