Bill,

 

I respect and think that your idea would work on the surface, but I think you over estimate the ability of a cell phone GPS receiver to be reliable enough for this kind of task.

 

First of all, GPS signals have a signal to noise ratio that is surprisingly small.  Secondly, you really have to mount a GPS antenna so that it sees the sky.

 

I realize it is tempting to look at the high availability of cells phones and see it as a simple solution, but if you were to start to understand the technical details, I think you may quickly realize the pit falls of the technology and question its ability to perform as desired. 

 

My personal opinion is that if that solution were to be tried, it would fail to deliver often enough that it would loose it’s appeal.

 

Kevin