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9/19/2017 7:27:10 PM
Posted: 12/21/2005 8:41:56 AM EDT
Over the weekend I went out to a bar with a friend who was in town with one of his coworkers who is European (French, to be exact ). Everything was fine and well until after a few drinks he started critiquing the U.S. (there was a TV on CNN in the bar, this is what sparked it). Somehow he started telling me about how Galileo was going to be this great thing and is so much more accurate than GPS. If I recall correctly, not only did the gov. allow more accuracy in 2000, but hasn't it gotten even more accurate since? Anyway, this guy was a limp wristed faggot from France and did indeed smell like he hadn't washed b/w his ass cheeks in a few days. I tried hard not to be so typically stereotyping of him but when you live up to just about every single characterization it's hard (arrogant, smelled funny, US bashing, islam apologist, etc...) I'll probably have to see him again this weekend so...
Link Posted: 12/21/2005 8:46:55 AM EDT
[Last Edit: 12/21/2005 8:52:52 AM EDT by mr_wilson]
IIRC your probably referring to the SA (selective availability) option which existed at one time in the GPS satellites.

Sorry I cannot recall but it has been quite a few years since SA was active.

SA was originally intended to prevent our enemies from using our own GPS satellites to target their nukes and when switched ON threw the coordinates off by varying ranges.....

Mike

E.T.A - modern Trimble GPS RTK units (used in surveying) have a horizontal (X,Y axis) accuracy of millimeters (depending on the number of satellites your operating on). At max sats, you accuracy is in the 2-3 millimeter range.

Elevation accuracy (Z-axis) with max satellites is around 10 centimeters
Link Posted: 12/21/2005 8:51:04 AM EDT

Originally Posted By mr_wilson:
IIRC your probably referring to the SA (selective availablity) option which existed at one time in the GPS satellites.

Sorry I cannot recall but it has been quite a few years since SA was active.

SA was originally intended to prevent our enemys from using our own GPS satellites to target thier nukes and when switched ON threw the coordinates off by varying ranges.....

Mike



Yes I know about SA, but I thought I heard it has still gotten better since. Through the actual receivers possibly? Also, are civs just on a higher tier of SA or do we really get what the armed forces get now?
Link Posted: 12/21/2005 8:51:48 AM EDT
With good Sat coverage I have gotten to within 1 ft of the geocaches using my Garmin Vista, With my Trimble I use at work, within inches.
Link Posted: 12/21/2005 8:52:16 AM EDT
With WAAS on the boat , accuracy is about 8 feet, which equates to directly off either port or starboard side from the helm. Automotive systems that tie to the brake, reverse and VSS wires in the car are more accurate in showing small movements, whereas on the water, you need to move about 4 feet for movement to show on the screen.
Link Posted: 12/21/2005 8:53:08 AM EDT
SA has been turned off completely. However, it is still possible to turn it back on with the flip of a bit.

So as it stands your GPS is just as accurate as the ones on my jet, but it the need arose yours could be back to being off by a hundred feet or so.
Link Posted: 12/21/2005 8:57:49 AM EDT
I know the US is worried or at least irked at Galileo because where as the US can lower the accuracy of the GPS constellation in war areas, the Galileo constellation will be just as accurate as ever and the bad guys will just use the Galileo for positioning if the EU will not bow to the US and degrade the accuracy. Or so goes the theory. Which is why the Air Force is working on destroying satellites. So much for keeping war out of space. (Not that I ever believed that in the first place) But on that note, the first submarines were frowned upon by the powers that be because they threated the existing naval order.

Wikipedia

Projects website
Link Posted: 12/21/2005 8:59:24 AM EDT
[Last Edit: 12/21/2005 9:00:30 AM EDT by IAMLEGEND]

Originally Posted By mr_wilson:
IIRC your probably referring to the SA (selective availability) option which existed at one time in the GPS satellites.

Sorry I cannot recall but it has been quite a few years since SA was active.

SA was originally intended to prevent our enemies from using our own GPS satellites to target their nukes and when switched ON threw the coordinates off by varying ranges.....

Mike

E.T.A - modern Trimble GPS RTK units (used in surveying) have a horizontal (X,Y axis) accuracy of millimeters (depending on the number of satellites your operating on). At max sats, you accuracy is in the 2-3 millimeter range.

Elevation accuracy (Z-axis) with max satellites is around 10 centimeters




Our RTK units here at work get horizontal accuracy well below 10 centimeters. You start getting into TOS (time on station) because to achieve this level of accuracy you have to be there for a bit.

You're right about SA. This is a measure put in place to stop our enemies from getting the benefit of high-accuracy GPS receivers. It is introduced and does not reflect on the potential accuracy.
Plus, differential weeds it out. That's why there are strict export regs concerning RTK units.
Link Posted: 12/21/2005 8:59:41 AM EDT
Selective availability was turned off by executive order in 2000.

The GPS system without selective availability is accurate to about 15 feet. Add-on technologies, such as WAAS and differential GPS, can improve that accuracy to about 1/2 inch.

Gallileo's free service will be accurate to about 13 feet (4m). Wow, a 10% improvement. For a subscription fee you will be able to get accuracy of three feet, and using something like differential GPS they'll be able to get down to about 10 centimeters. Notice that differential GPS (ours) is still much better than the full subscription version of Gallileo.

All I can say about Gallileo being better than GPS is "Whoopee Doo". It's going to come online, if they get it online, in 2008. I should hope that twenty extra years of development would get them a system with some improvements. I'd say that's pretty scarce improvement for the investment. What they really want is safety from when we turn the GPS system off in time of war. Safety from us...

Jim
Link Posted: 12/21/2005 9:11:21 AM EDT
SA was a joke anyway since DGPS was available. I had a differential receiver on my boat prior to SA being turned off and I got great accuracy, under 10' IIR. So we have one agency degrading the signal, and at the same time have another agency receiving, cleaning up, and rebroadcasting the signal.....makes sense to me.

FWIW my WAAS signal is slightly better than differental.
Link Posted: 12/21/2005 9:32:24 AM EDT
[Last Edit: 12/21/2005 9:33:08 AM EDT by INI]
Marine units can also have their movement on the screen improved with the addition of a fluxgate compass, with it's internal gyroscope relaying real time vessel position info to the GPS unit, which makes fine positioning not appear as clunky, and a little faster responding. When I install an autopilot, the AP and fluxgate and GPS are all tied together. The software makes it work.

The car specific units have the gyro. The new Alpine that just came out about a month ago is very seamless.
Link Posted: 12/21/2005 9:44:23 AM EDT
A good DGPS subscription like Omnistar's combined with a good Trimble receiver can approach centimeter accuracy.

Beats the hell out of WAAS, especially in the northern lattitudes.

Link Posted: 12/21/2005 10:13:38 AM EDT

Originally Posted By DocBrooks: Anyway, this guy was a limp wristed faggot from France and did indeed smell like he hadn't washed b/w his ass cheeks in a few days. I tried hard not to be so typically stereotyping of him but when you live up to just about every single characterization it's hard (arrogant, smelled funny, US bashing, islam apologist, etc...) I'll probably have to see him again this weekend so...
Is he married to a woman? Does he have any children? Does he live with his mother? So many EU stereotypes, so little time.
Link Posted: 12/21/2005 10:16:00 AM EDT
Link Posted: 12/21/2005 10:16:35 AM EDT

Originally Posted By INI:
With WAAS on the boat , accuracy is about 8 feet, which equates to directly off either port or starboard side from the helm. Automotive systems that tie to the brake, reverse and VSS wires in the car are more accurate in showing small movements, whereas on the water, you need to move about 4 feet for movement to show on the screen.



Yep
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