Saturday, December 6, 2008

Is GPS evidence gathering something new? PROPONENT

For centuries, man has been asking and answering the question, where am I, and corollary questions, where are they (who I am seeking), and where am I in relation to them. To do this, man devised maps, co-ordinate grid systems on those maps, and methods to take position information and record it to determine where the person was on those maps. The process involves four activities:

  • Finding a reference point. One who is lost has no reference point, finding a reference point is the start of finding out where one is. In the past, mountains, the moon, the stars and the sun all were used as reference points. Today, GPS satellites provide the reference points.

  • Getting a "fix"- "Fixing" your position usually requires using two or more reference points in conjugation to determine your location related to some other desired end, usually, your destination.

  • Plotting the "fix"- Taking the information about the reference point and calculating a position, usually involving reference to tables calculated from known information. Plotting the fix usually involves a time component.

  • Recording the "fix" recorded or plotted for future reference, including the time component.

  • Finding a "course" - Additional fixes are plotted and recorded, then connected to find a course, or your path in a general direction. Together with the time component, you can chart both your direction towards a goal and your speed towards that goal.

For centuries, man has been doing manually what a GPS does automatically. Lewis & Clark carried a sextant, "shot" the sun and the stars, fixed their current location on a grid, and found their course across the Louisiana Purchase to the Pacific.

From these observations we reach the first truth: The Global Positioning System does nothing new-it simply automates the ancient process of finding out where we are. It does it faster and more accurately, and automatically, yes, but it does nothing that is significantly new.


  • The GPS "constellation" of satellites is a smarter version of the sun, moon and stars, but it provides the same reference point as the stars.

  • The GPS "fix" calculates position using the constellation in the same fashion. In addition, the satellites provide a uniform time reference, which greatly increases accuracy, but does not change the procedure. A timed satellite code pulse provides the same information as a pocket watch on the ground-time reference. A GPS receiver calculates the position using a computer, which, while faster than Lewis & Clark's tables, performs the same function.

  • A GPS "fix" is recorded in computer memory, which serves the same function as Lewis & Clark's notebook.

  • Course calculation, although done by computer, uses the same type of computation applied to the information in memory that Lewis & Clark performed to plot their course.

The speed, accuracy and automation of GPS generated evidence do not provide a legal basis for excluding them from trial proceedings. As long as a foundation for the basis of operation of each of the above items is introduced, there should be no bar to the GPS generated evidence of locations- the GPS "track."

Because by observation a person could do the same reference point location, fix, plot, and course tracking to a third observed party or vehicle manually, because a GPS can do so more quickly and efficiently should not bar third party tracking simply based on the automated process. If the manual process would be barred, the GPS automated process should be barred.

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