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Author Topic: can a gps hiccup?  (Read 4616 times)

cassandra and sara's daddy

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can a gps hiccup?
« on: March 21, 2012, 05:19:47 PM »
have an anomaly (like temporary loss of power) that would cause it to indicate a very high max speed?  like say 99.7 mph? garmin nuvi
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Harold Tuttle

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Re: can a gps hiccup?
« Reply #1 on: March 21, 2012, 05:25:00 PM »
looking at a kids driving record in the management app?

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erictank

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Re: can a gps hiccup?
« Reply #2 on: March 21, 2012, 05:27:59 PM »
An actual, dedicated GPS unit?  The GPS function on my phone has, at times, indicated anomalously-high and -low walking speeds during exercise, but my wife's Garmin GPS unit is actually really accurate in displayed speed, as far as we can tell.
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Nick1911

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Re: can a gps hiccup?
« Reply #3 on: March 21, 2012, 05:30:07 PM »
It's probably possible.  I mean, it's electronic, it could fail.  Seems unlikely though.  The question is, are there more likely reasons for your GPS to have recorded that speed?
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41magsnub

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Re: can a gps hiccup?
« Reply #4 on: March 21, 2012, 05:31:54 PM »
I had one back in my army days that was 7 klicks off.  It was one of the early shoe box sized units.
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cassandra and sara's daddy

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Re: can a gps hiccup?
« Reply #5 on: March 21, 2012, 05:38:52 PM »
Quote from: Harold Tuttle on March 21, 2012, 05:25:00 PM
looking at a kids driving record in the management app?



wife borrowed my jeep. saw it next morning
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It is much more powerful to seek Truth for one's self.  Seeing and hearing that others seem to have found it can be a motivation.  With me, I was drawn because of much error and bad judgment on my part. Confronting one's own errors and bad judgment is a very life altering situation.  Confronting the errors and bad judgment of others is usually hypocrisy.


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roo_ster

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Re: can a gps hiccup?
« Reply #6 on: March 21, 2012, 05:57:13 PM »
Quote from: 41magsnub on March 21, 2012, 05:31:54 PM
I had one back in my army days that was 7 klicks off.  It was one of the early shoe box sized units.

I remember those.  They worked a lot better if you had a map & compass handy.
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MicroBalrog

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Re: can a gps hiccup?
« Reply #7 on: March 21, 2012, 06:01:27 PM »
It is possible for them to lose contact with one or more satellites if it helps, and then take a few minutes to come back. Don't know if that does anything.
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charby

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Re: can a gps hiccup?
« Reply #8 on: March 21, 2012, 06:29:27 PM »
Bad satellite geometry can cause GPS units to go wonky.

It takes 4 satellites to get the GPS results, if one of those breaks contact or in a poor location then less than accurate readings can occur.

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Jim147

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Re: can a gps hiccup?
« Reply #9 on: March 21, 2012, 06:55:56 PM »
Aliens. Their spaceships are always messing with our satellites.

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Re: can a gps hiccup?
« Reply #10 on: March 21, 2012, 07:16:57 PM »
Quote
It takes 4 satellites to get the GPS results

IIRC, it takes 3 sats to get position and speed, and 4 to get altitude. Generally you will get 4 or more in most areas.

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griz

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Re: can a gps hiccup?
« Reply #11 on: March 21, 2012, 07:23:23 PM »
They can do funny things when they "catch up" after a weak signal.  I have lost coverage in a tunnel and had it assume I more or less instantly arrived at the point where coverage resumed.  I've also had it read a max speed of just over 20 MPH when the tree cover was very heavy.  I was walking at the time.
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MillCreek

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Re: can a gps hiccup?
« Reply #12 on: March 21, 2012, 07:38:36 PM »
Quote from: cassandra and sara's daddy on March 21, 2012, 05:38:52 PM
wife borrowed my jeep. saw it next morning

Can a Jeep make this speed other than in free fall?
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Re: can a gps hiccup?
« Reply #13 on: March 21, 2012, 09:57:04 PM »
Quote from: cassandra and sara's daddy on March 21, 2012, 05:38:52 PM
wife borrowed my jeep. saw it next morning

The only way to get a jeep to 97 is to heave it off a cliff. Is there any damage to indicate is was heaved off a cliff.
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Re: can a gps hiccup?
« Reply #14 on: March 21, 2012, 10:04:43 PM »
Yes, they can and do hiccup. 
Even the pro models lose contact once in a while and throw erroneous readings while they regroup on satellites.
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CNYCacher

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Re: can a gps hiccup?
« Reply #15 on: March 21, 2012, 10:50:45 PM »
The GPS system can only indicate position, not speed.
Speed is calculated by knowing where you are now, and comparing that to where you were and how long ago it is that you were there.
If the position is innacurate and trending in one direction, and then is off in another direction, the calculated speed will be wrong, perhaps wildly wrong.

It is very common for GPS systems to drift off like that, and then correct.  I've seen my avatar on the map pace me along a highway 200 yards to the right, then slowly drift back over.  If it had instead drifted behind me, and then caught up, the system would have thought I was going much faster than I was.

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JonnyB

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Re: can a gps hiccup?
« Reply #16 on: March 21, 2012, 11:10:24 PM »
A few years ago, I was flying to Two harbors, MN from Willmar. Tooling along in my 90hp Champ, which had a climb prop and cruised in the high 80s and maybe 92 -93 at higher RPM. I noticed I was a bit to the left of my intended track, and moving along at 99mph. Hmmm... Wind is more than I thought. Corrected to the right, and glorified in the nice tailwind.

Pretty soon, the GPS is indicating 112mph and I'm still tracking left. Correct again. But, I'm getting suspicious.

When the Apollo showed me with a ground-speed of 141 mph, I turned it off, waited a minute and powered back on. Now, I'm way right and back at 88mph.

I said all that in order to say that, yes, a GPS can show faulty information.

jb
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Harold Tuttle

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Re: can a gps hiccup?
« Reply #17 on: March 22, 2012, 12:43:35 AM »
My Garmin has an application on my laptop that waypoints the entire trip for speed and location

Using that, you can see where the high speed was recorded.
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wmenorr67

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Re: can a gps hiccup?
« Reply #18 on: March 22, 2012, 06:25:18 AM »
Quote
Now, I'm way right and back at 88mph

Couldn't get enough voltage to the flux capacitor?
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JonnyB

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Re: can a gps hiccup?
« Reply #19 on: March 22, 2012, 10:03:31 AM »
Quote from: wmenorr67 on March 22, 2012, 06:25:18 AM
Couldn't get enough voltage to the flux capacitor?

Voltage was OK but the generator was only good for 20 Amps.  =D

jb
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KD5NRH

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Re: can a gps hiccup?
« Reply #20 on: March 22, 2012, 10:20:22 AM »
Quote from: CNYCacher on March 21, 2012, 10:50:45 PM
The GPS system can only indicate position, not speed.
Speed is calculated by knowing where you are now, and comparing that to where you were and how long ago it is that you were there.
If the position is innacurate and trending in one direction, and then is off in another direction, the calculated speed will be wrong, perhaps wildly wrong.

This; I've seen a 75mph max speed on my bicycle.
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sanglant

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Re: can a gps hiccup?
« Reply #21 on: March 24, 2012, 05:00:37 PM »
Quote from: MillCreek on March 21, 2012, 07:38:36 PM
Can a Jeep make this speed other than in free fall?
yes :angel:
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