GPS Tracking ROI

I was recently talking to a pilot who uses GPS in his work and the subject of map projections and datums came to mind. There’s a lot of technical ground here that goes way beyond what the average GPS user knows or even wants to know, but like any technical subject, the way to get started is to take the first step. I came upon this excellent beginner’s synopsis:

FAQ: WHAT ARE MAP DATUMS AND PROJECTIONS?
“NON-TECHNICAL ANSWER” (14 June 1999)
Different datums are based on different mathematical models of the
earth’s shape and dimensions (ELLIPSOIDS) plus an additional factor of
PROJECTION.

In Japan, say, they used a projection point that isn’t at
the center of the earth, but somewhere under Japan. This gives less
distortion of projecting a sphere onto a “flat map” there, but using
that projection for the US would result in a very weird map!…

Read more at the gpsinformation.net site, an excellent reference I came across today.  I was particularly taken by the reference in the article to the Japanese projection system.  I happened to be around for a real-world incident that cost a pilot’s life and I never understood why until I read this tutorial.Some years ago when I worked in the communications planning arena in Japan, an F-16, based in Japan, was on a training mission in Korea.  The aircraft flew right into a mountain, nearly a kilometer off course in a carefully planned training exercise.  The initial cause (when isn’t it?) was “pilot error”.  It could have been let go at that.

But some excellent detective work by the Defense Mapping Agency (now part of the National  Geospatial Intelligence Agency) proved that staff mission planners used a Korean map (kind of common in Korea, you know) that had been made using the current Japanese projection system. (Japan once occupied Korea and many ‘tag-ends’ of Japanese influence remain.)  The planners carefully plotted the course the aircraft was to fly, identified the points for the pilot to make his turns, etc., from the geographic coordinates on the Korean map, and then passed those latitude and longitudes to the aircraft folks who dutifully entered them into the aircrafts sophisticated navigation system.

Everyone did their work to what the believed to be the highest standards.  Can you spot the mountain coming up after reading the tutorial?  Yep, you guessed it.  The American-built F-16 system used the current GPS datum, WGS-84.  At the point where the metal and flesh struck the granite, it what was first assumed to be a navigational error of approximately one kilometer, the two projections were found to be just about one kilometer different.  The difference would have been a mere exercise in academic trivia, except that a man and an aircraft were involved.

So if you send people into the field, ground-based or airborne, take the time to know what projections and datums your maps are based upon.  It’s only trivial if you don’t have to worry about rocks in the windscreen.