[MLB-WIRELESS] Interesting GPS post by John Dalton

[Steven Haigh]

His message is below, but because he sent the mail from a different address 
than he's subscribed with, it bounced from the list..... (the huge 
disadvantage...) on the same note, Dwayne's posts are doing the same....

** Begin email **

The precise positioning service (PPS) (military) has been
measured to give an accuracy of 8.3m Spherical Error
Probable (SEP) and 4.6m Circular Error Probable (CEP)[1].
These measurements were made using code tracking (ie. standard)
receivers during the "Desert Storm" campaign of the Gulf
War in 1991.

Expected RMS horizontal errors of the standard positioning
service (SPS) (civilian) is around 10m [1].

*Differential* GPS , using the SPS, is precise to 1m (one
standard deviation) for two points within 50km of each
other. [2]

Carrier Tracking receivers can give a *differential*
precision of less than a centimetre.

Summary:

1) You will not get an accuracy of 0.5m out of a single GPS receiver.
2) Differential GPS *may* give you an acceptable result. Differential
 receivers are readily available.
3) Carrier tracking GPS will give accurate positions. I'm not sure
 whether such receivers are available off the shelf. Such a receiver
 can only give you a difference in height.

Have you considered using a laser to check your line of sight?

Regards
John



References:
[1] Global Positioning System: Theory and Applications Volume 1
 Edited by Parkinson and Spilker
 page 18

[2] Global Positioning System: Theory and Applications Volume 2
 Edited by Parkinson and Spilker
 page 4


Glossary
SEP = radius of sphere which contains 50% of measurements
 In other words, accuracy in 3 dimensions.

CEP = radius of circle which contains 50% of measurements
 In other words, accuracy in 2 horizontal dimensions. 

** End Email **

-- 
Signed,
Steven Haigh
President - Melbourne Wireless
www.wireless.org.au


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