Tales from the Geodetic Crypt

Andrew Zolnai

Events: 1989 - 1999Events: 1989 - 1999

(early GIS Day talk)

It’s the datum, stupid

• Errors in datums are in the order of meters, much harder to detect that errors in projections in the harder to detect that errors in projections in the order of hundreds of meters

• US cruise missile that hit the Chinese embassy in Belgrade during the Balkan War, apparently flew down the wrong street

• One military group provided the geodetics that were apparently mistranslated by another group were apparently mistranslated by another group in using the wrong datum

• Ironically it’s the very small size of the error that made it undetectable

Gentlemen, start your GPS

• Soldiers scouted locations in Afghanistan to triangulate targets on the ground, radioed to triangulate targets on the ground, radioed to AWACS above for use by laser-guided bombs

• One such troupe came under fire, jumped into a watery ditch, and dropped a GPS unit that reset itself when it short-circuited in the water...

• But wait! it then sent its coordinates to the AWACS, not the target’s it had just triangulated...AWACS, not the target’s it had just triangulated...

• The laser bomb hit the ditch alright - that’s how precise it was – so the blast went straight up not sideways, and the scouts lived to tell the tale

$100 beats $100M

• Air Force and Navy fighter pilots used to play war games over the Arctic, deemed the most likely games over the Arctic, deemed the most likely path for a Cold War-era invasion at the time

• The Navy outfitted its jets with radar detectors, the kind you buy for a car at any electronics store

• That apparently gave Navy pilots a split-second advantage in detecting Air Force jets firstadvantage in detecting Air Force jets first

• The upper hand was gained purely based on hardware that was a fraction of the cost of the fighter jets being flown then

$100 crashes $¼B

• The space craft carrying a Mars lander flew straight into the Red Planet at full speedstraight into the Red Planet at full speed

• It apparently had miscalculated its altitude by using the wrong conversion parameter

• The lesser-known part is, however, that when Ground Control noticed the error, the modem had a glitch and failed to relay the corrections

• Anyone who’s used a modem will know how • Anyone who’s used a modem will know how often they simply stop and need rebooting

• A $250M mission relied on off-the-shelf hardware to communicate as far as 250M miles