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Cappy
Excelent
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Joined: 16 May 2002
Posts: 27368
Location: Spreadsheetylvania
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 Posted: 10/21/04 - 18:13 Post subject:
| MechEngDropout wrote: |
Seems like a pretty significant distance. GPS would have to get much more accurate before I'd consider it. |
No the GPS is balls on accurate, the bike computer is off.
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MechEngDropout
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Joined: 27 Jun 2003
Posts: 10474
Location: Off the grid
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Posted: 10/21/04 - 18:15 Post subject:
| Cappy wrote: |
No the GPS is balls on accurate, the bike computer is off. |
How do you know that? And what have you measured the GPS against that you know it is absolutely correct?
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Cappy
Excelent
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Joined: 16 May 2002
Posts: 27368
Location: Spreadsheetylvania
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Posted: 10/21/04 - 18:16 Post subject:
| MechEngDropout wrote: |
How do you know that? And what have you measured the GPS against that you know it is absolutely correct? |
The GPS claims a 97% accuracy. I would say that pretty darn accurate in my book
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copteacher
Adjunct
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Joined: 08 Jun 2002
Posts: 20588
Location: Teaching in the Halls of Justice
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Posted: 10/21/04 - 20:21 Post subject:
I believe I was on the team that you beat. So we win then right?
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purple hayes
Frightened Inmate #2
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Joined: 14 May 2002
Posts: 14462
Location: ON YOUR LEFT!
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Posted: 10/21/04 - 21:16 Post subject:
| Cappy wrote: | | No the GPS is balls on accurate, the bike computer is off. |
I would think that bike bike with a wheel that was constantly in touch with the pavement that you were traveling on would be more accurate than satellites that are miles up in the atmosphere and are intentionally controlled by the government to not be 100% accurate.
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Sahara
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Joined: 17 May 2002
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Posted: 10/21/04 - 23:07 Post subject:
| purple hayes wrote: |
I would think that bike bike with a wheel that was constantly in touch with the pavement that you were traveling on would be more accurate than satellites that are miles up in the atmosphere and are intentionally controlled by the government to not be 100% accurate. |
a conspiracy!!!
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MechEngDropout
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Joined: 27 Jun 2003
Posts: 10474
Location: Off the grid
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Posted: 10/22/04 - 00:19 Post subject:
| purple hayes wrote: |
I would think that bike bike with a wheel that was constantly in touch with the pavement that you were traveling on would be more accurate than satellites that are miles up in the atmosphere and are intentionally controlled by the government to not be 100% accurate. |
Agreed. If you have the computer calibrated correctly with a good rollout measurement, it should be very precise, within .5% I would think.
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genie
Master of Prissface
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Joined: 14 May 2002
Posts: 16194
Location: Finding serenity one day at a time
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Posted: 10/22/04 - 10:07 Post subject:
| phillycat wrote: | | Thanks guys! I might have to get me one of them there gadgets! |
GASP! And support the capitalistic corporate monster who manufactures them? 
Kidding, for reals......you'll love it, they do so much more than any other gadget out there. Mine even works relatively well on the trails I run, which I had been told it wouldn't.
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genie
Master of Prissface
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Joined: 14 May 2002
Posts: 16194
Location: Finding serenity one day at a time
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Posted: 10/22/04 - 10:08 Post subject:
| Cappy wrote: |
No the GPS is balls on accurate, the bike computer is off. |
PC is a girl, silly....she doesn't have those
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phillycat
Member
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Joined: 14 Jul 2004
Posts: 1953
Location: Da hood
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Posted: 10/22/04 - 10:18 Post subject:
| genie wrote: |
GASP! And support the capitalistic corporate monster who manufactures them?
Kidding, for reals......you'll love it, they do so much more than any other gadget out there. Mine even works relatively well on the trails I run, which I had been told it wouldn't. |
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robp
Pyromaniac
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Joined: 26 Jul 2002
Posts: 16242
Location: Waiting in line at the beer store...
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Posted: 10/22/04 - 10:27 Post subject: fyi
there is a difference between military quality gps signals and civilian. I would believe that a properly calibrated bike odometer would be more accurate.
GPS Positioning Services Specified In The Federal Radionavigation Plan
Precise Positioning Service (PPS)
Authorized users with cryptographic equipment and keys and specially equipped receivers use the Precise Positioning System. U. S. and Allied military, certain U. S. Government agencies, and selected civil users specifically approved by the U. S. Government, can use the PPS.
PPS Predictable Accuracy
22 meter Horizontal accuracy
27.7 meter vertical accuracy
200 nanosecond time (UTC) accuracy
Table of Contents
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Standard Positioning Service (SPS)
Civil users worldwide use the SPS without charge or restrictions. Most receivers are capable of receiving and using the SPS signal. The SPS accuracy is intentionally degraded by the DOD by the use of Selective Availability.
SPS Predictable Accuracy
100 meter horizontal accuracy
156 meter vertical accuracy
340 nanoseconds time accuracy
These GPS accuracy figures are from the 1999 Federal Radionavigation Plan. The figures are 95% accuracies, and express the value of two standard deviations of radial error from the actual antenna position to an ensemble of position estimates made under specified satellite elevation angle (five degrees) and PDOP (less than six) conditions.
For horizontal accuracy figures 95% is the equivalent of 2drms (two-distance root-mean-squared), or twice the radial error standard deviation. For vertical and time errors 95% is the value of two-standard deviations of vertical error or time error.
Receiver manufacturers may use other accuracy measures. Root-mean-square (RMS) error is the value of one standard deviation (68%) of the error in one, two or three dimensions. Circular Error Probable (CEP) is the value of the radius of a circle, centered at the actual position that contains 50% of the position estimates. Spherical Error Probable (SEP) is the spherical equivalent of CEP, that is the radius of a sphere, centered at the actual position, that contains 50% of the three dimension position estimates. As opposed to 2drms, drms, or RMS figures, CEP and SEP are not affected by large blunder errors making them an overly optimistic accuracy measure
Some receiver specification sheets list horizontal accuracy in RMS or CEP and without Selective Availability, making those receivers appear more accurate than those specified by more responsible vendors using more conservative error measures.
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HighHeat
Big Daddy
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Joined: 30 May 2004
Posts: 6682
Location: Out of the frying pan, and into the fire.
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Posted: 10/22/04 - 11:01 Post subject:
I love mine.
The only bad thing is that it can take 10-15 minutes to grab a signal if it's cloudy, but oh well, trade offs for the absolute coolness of it all.
AND if you buy it at REI and have an issue with it, they'll swap it for a new one, even months after you bought it. 
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