smgtheophilus
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There have been a few comments about the GPS monitoring, so I thought I'd throw some information into the pot, since I've worked with and even designed GPS equipment since its inception... The 36 foot variance from GPS systems is due to Selective Availability - an intentional flaw in the signal from GPS satellites that 'guarantees' that no commercial GPS receiver can ever be accurate to more than ~10 meters. This would keep rogue states and terrorists from using the devices to gain cheap, accurate, targeting from commercial systems.
MIL-SPEC receivers use a different channel that allows them to get much better information - with Kalman filtering the receiver can be accurate within centimeters.
HOWEVER - Selective Availability has been disabled since the Clinton era. Partially this was a 'convenience' with the reservation that SA could be turned on if the government deemed it in the nation's best interest. In the Gulf Wars SA was also turned off to allow military operations to be more accurate, especially when troops started getting commercial GPS receivers from their relatives to use. Since then they've determined that jammers are better at messing up GPS-aided guidance than turning on SA, so it's likely to remain off 'permanently'.
Anyone that has a recent GPS with mapping information can see for themselves that, without SA, they can track their position along the road to within several feet - enough to know which side of a two-lane divided highway they're driving down.
Given this, I would suggest that the plots they have of PG's position are about as accurate, and that if LE decided GPS data was worthless because of the supposed 36 foot variance, then they were grossly misinformed.
EDIT: Here's an article discussing the turning off of SA on May 2st, 2000:
http://geography.about.com/library/weekly/aa050400a.htm
The figures they indicate, of the 'more accurate' readings being within 10-20 meters, is without Kalman filtering, differential GPS techniques, etc, which most commercial GPS receivers did not implement. Now, accuracy can usually be had within several feet if the information is relayed through cell phone connection (the cell tower providing the differential offset).
Caveat: what is possible, and what LE paid for in their GPS monitoring systems, are two very different things.
MIL-SPEC receivers use a different channel that allows them to get much better information - with Kalman filtering the receiver can be accurate within centimeters.
HOWEVER - Selective Availability has been disabled since the Clinton era. Partially this was a 'convenience' with the reservation that SA could be turned on if the government deemed it in the nation's best interest. In the Gulf Wars SA was also turned off to allow military operations to be more accurate, especially when troops started getting commercial GPS receivers from their relatives to use. Since then they've determined that jammers are better at messing up GPS-aided guidance than turning on SA, so it's likely to remain off 'permanently'.
Anyone that has a recent GPS with mapping information can see for themselves that, without SA, they can track their position along the road to within several feet - enough to know which side of a two-lane divided highway they're driving down.
Given this, I would suggest that the plots they have of PG's position are about as accurate, and that if LE decided GPS data was worthless because of the supposed 36 foot variance, then they were grossly misinformed.
EDIT: Here's an article discussing the turning off of SA on May 2st, 2000:
http://geography.about.com/library/weekly/aa050400a.htm
The figures they indicate, of the 'more accurate' readings being within 10-20 meters, is without Kalman filtering, differential GPS techniques, etc, which most commercial GPS receivers did not implement. Now, accuracy can usually be had within several feet if the information is relayed through cell phone connection (the cell tower providing the differential offset).
Caveat: what is possible, and what LE paid for in their GPS monitoring systems, are two very different things.
