Miata Mailing List: February 1997, Message #262
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   From: (none)

Subject: Re: Inaccuracies of GPS 

   Date: (none)



My father had some good experience with GPS units in the Oil & Gas

surveying industry

in Alberta. In Relative mode a civilian GPS unit is highly accurate, but

requires an

established accurate starting point, then you can take relative coords

based on the point. If

your a surveyor its not that hard to find benchmark points where the coords

are know. As

far as the military having different algorithms, this is very correct,

because a civil GPS 

unit in Absolute mode is kinda useless for surveying (however, it is good

if you need a

chopper to get you close to a job location deep in the bush).



						Seth.



----------

> From: RSAlder@aol.com

> To: Multiple recipients of list 

> Subject: Re: Inaccuracies of GPS 

> Date: Sunday, February 02, 1997 5:23 PM

> 

> In a message dated 97-02-02 02:12:14 EST, n6mod@amt.org (Aleksandr

Milewski)

> writes:

> 

> > 	The DoD has decided that it would be a Really Bad Idea to put up a

> >  satellite navigation system that would provide highly accurate

positition

> >  data with an average, consumer reciever. So, they munge the data a

little

> >  bit on the signals that are easy to decode, and keep the good stuff

for

> >  themselves. However during the only war to take place since GPS has

become

> >  operational, SA was turned off so the US Military could use average,

> >  consumer GPS units. :-\

> 

> I had dinner with an old friend the other night and he told me that he is

now

> working with some engineering company or other, on a contract/consulting

> basis, which is working on a GPS problem the government is worried about.

 It

> seems that GPS is very vulnerable to jamming and that for a measly

$500,000

> or so of equipment, Saddam could have rendered the navigational

capabilities

> of the Desert Storm forces useless.

> 

> I found that quite interesting (he was talking about band widths and a

whole

> bunch of esoterica far beyond my comprension) and took the opportunity to

ask

> him about the accuracy of using GPS for speedometer calibration.  After

some

> thought and more talk of electronic and physics theory, again largely

beyond

> my understanding, said quite convincingly that he could see no reason to

> preclude the use of GPS in checking your speedometer for accuracy.  In

fact

> he was quite excited to find an other use for his own GPS unit.

> 

> He also mentioned something about secret, changed-daily, algorithms

(don't

> test me on this) which military units have which allows them to be so

much

> more accurate than mere civilian models.  The government simply won't

release

> them to the manufactures of civilian models hence, the reduced accuracy. 



> 

> FWIW, I would be happy to forward any more detailed questions anyone

might

> have.

> 

> Ralph Alder

> SoCal 90 Red A

> 

> 

> 

> 

>