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Wrong average speed
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peterc10
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PostPosted: Tue Nov 15, 2011 7:40 pm    Post subject: Wrong average speed Reply with quote

Have been meaning to report this for a while. I thought somebody else did but could not find the post.

I am now the proud owner of the world land speed record. According to CamerAlert I managed 945mph average on the SPECS section of the M25 (M1 slightly slower). The instantaneous speed was telling me I was only doing 50mph, but I am told that it is the average that counts. Should I write into the Guinness Book of Records?

Or maybe there is a problem with the average speed calculation? Wink

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CAA_0824011705
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PostPosted: Sun Jan 01, 2012 11:32 pm    Post subject: Reply with quote

i was also having this problem to day tn the a 419 & m4
is is possable to have a fix for this
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adm143
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PostPosted: Fri Jan 13, 2012 11:46 pm    Post subject: Reply with quote

CAA_0824011705 wrote:
i was also having this problem to day tn the a 419 & m4
is is possable to have a fix for this


I'm seeing the same thing 75% of the time on the A127

In an average speed zone the display will show my "instantaneous” speed and the average speed as I pass the camera. Both displays will be updated correctly for perhaps quarter or half a mile. Suddenly the average speed will go red and start reporting speeds of 900+ mph. The values will revert back to being correct at the next camera post.

There doesn't appear to be any pattern to the failure. It happens if I'm cruising at 50mph on a virtually empty road or if I'm doing 1mph during the rush hour(s). It may fail 100yds after passing a camera post or wait until I'm a mile further down the road.

I have a HTC Desire S and the problem occurs when using the internal GPS and also when using a much more sensitive external Globalsat BT359 GPS unit connected via Bluetooth http://www.pocketgpsworld.com/globalsat-bt-359-gps-review.php

If the 900+ mph average speed occurs and I stop in a traffic jam the 900 figure will gradually fall indicating that the software it is still attempting to work out an average speed, but based on an erroneous starting figure.

Wild speculation: Could one of the reported GPS positions be behind the previous one thus the algorithm now thinks I'm travelling backwards and negative numbers are wrapping in the software to become large positive numbers? Should there be a zero trap for negative position values?
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lbendlin
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PostPosted: Sat Jan 14, 2012 1:54 am    Post subject: Reply with quote

The GPS doesn't have a concept of "forward" or "backward". It only thinks in headings. So any distance value that we get back from the GPS is always an absolute distance. However we have seen quite a few chipsets that are, let's say, rather inventive about the distance they claim to have traveled in a second. That is a much more likely cause.

A klutzy workaround in such a situation is to stop and restart the averaging manually by tapping on the speed icon twice.
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CAA_0511165900
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PostPosted: Mon Jul 23, 2012 1:13 pm    Post subject: SPECS says 895 mph! Reply with quote

Clearly CP still has a problem with SPECS, any chance it will ever get fixed?
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PaulB2005
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PostPosted: Mon Jul 23, 2012 1:36 pm    Post subject: Reply with quote

Please feel free to elaborate.
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CAA_0511165900
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PostPosted: Tue Jul 24, 2012 10:57 am    Post subject: Reply with quote

Of Course!

Travelling along the A14 towards Cambridge at the first SPECS camera it showed my speed and average as expected and at the next, then suddenly the average speed showed red and displayed crazy numbers changing constantly! I pressed the screen and the display recovered and then immediately did the same!

I had CoPilot Live on a Samsung Galaxy SII and on entering the SPECS zone brought CameraAlert to the front.

Chris
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peterc10
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PostPosted: Tue Jul 24, 2012 11:22 am    Post subject: Reply with quote

All of us appear to be reporting the same problem - the instant speed is correct, it is the average speed that is wrong. In those circumstances I am struggling to see how it can be the chipset getting the distance it travelled in a second wrong, otherwise the instant speed (or both speeds) would be wrong. Or have I misunderstood how it all works?

And we all three have different phones - Desire, Sensation and Galaxy.
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AliOnHols
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PostPosted: Tue Jul 24, 2012 2:33 pm    Post subject: Reply with quote

I'm no mathematician or scientist but I think that this is how it works -

Let's say that you are traveling in a straight line at 90kmh (25m/sec). Now, while everything is TicketyBoo, every second the chipset is calculating that your position is 25m further along the road than the last time it checked. Your average speed remains 90kmh.
If there is a glitch for a second and for some reason the chipset calculates that you are 100m away from your actual position, it shall report that you will have traveled at 100m/sec or 360kmh and the average speed shall be affected accordingly. If in the next second it accurately records your location, you have now traveled 100m+25m+25m in the last second at a speed of 540kmh. Your average speed is now WAY OUT and shall take a very, very long time, if at all, to get back to anything meaningful, so best to stop the app and restart.

CamerAlert only takes the information given to it by the chipset and performs the calculation to give the average speed. If the information is wrong, the calculation is wrong. RiRo.

The mathematicians amongst us shall say that the above example is only true at times when Pythagoras-Sees Old Harry-Catch A Herring-Trawling Off America correctly, but I don't care. I know what I mean, I hope you do too.
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peterc10
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PostPosted: Tue Jul 24, 2012 2:49 pm    Post subject: Reply with quote

Alionhols

But that means that the instant speed reading would change too, albeit for a second, but it doesn't. And it would also mean that the speed would increase by a small amount if you were half way along a section, because the error would be mathematically less significant than at the beginning of the section, but that does not happen either. And finally it also means that the readings of average speed would start to fall each second (as the error became mathematically less significant) until the problem occurs again, but they don't.

It seems to have no rhyme or reason to it. Half way between cameras it will suddenly leap from 50mph to 900mph, suggesting a huge error in distance, then a couple of seconds drop to 500mph, suggesting it was not so huge, then a couple of seconds back up to 750mph! And during the whole time the instant speed will remain a steady 50mph.
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M8TJT
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PostPosted: Tue Jul 24, 2012 2:56 pm    Post subject: Reply with quote

I've been through the specs on the A14 between A1 and M11 4 times over the last couple of days and CA behaved perfectly. But that does not really help those for whom it isn't behaving perfectly Confused
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AliOnHols
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PostPosted: Tue Jul 24, 2012 3:09 pm    Post subject: Reply with quote

peterc10
Like M8TJT's, my CamerAlert also performed perfectly when in the Uk recently so I believe that there is nothing wrong with the software or the formulas employed.

Sorry, I don't have an alternative suggestion other than the chipset/gps receiver on your phone giving the occasional false reading.
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peterc10
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PostPosted: Tue Jul 24, 2012 3:10 pm    Post subject: Reply with quote

M8TJT wrote:
I've been through the specs on the A14 between A1 and M11 4 times over the last couple of days and CA behaved perfectly. But that does not really help those for whom it isn't behaving perfectly Confused
Galaxy Ace2

Does the Galaxy Ace 2 have the same GPS chipset as the Galaxy SII that Chris says he is using?

I too have been through that section of the A14 a while ago, but I had cameralert running in the background with overspeed alerts on. I got no alerts, but I think they are based upon the instant speed not average aren't they?
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M8TJT
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PostPosted: Tue Jul 24, 2012 4:23 pm    Post subject: Reply with quote

peterc10 wrote:
Does the Galaxy Ace 2 have the same GPS chipset as the Galaxy SII that Chris says he is using?
I don't know. Google is your friend Very Happy
peterc10 wrote:
I too have been through that section of the A14 a while ago, but I had cameralert running in the background with overspeed alerts on. I got no alerts, but I think they are based upon the instant speed not average aren't they?
I don't think so. I would have hoped that they are are based on average speed in a specs zone as your instantaneous speed is irrelevent. I had CA in the foreground, and on the lucky occasions that I was able to get up a bit of speed and get the calculated average speed just above 70, the readout turned red. Can't remember about alerts as I turned down the sound as HWMBO was getting teed off with the constant nagging of the SPECS warnings.

@Ali.
I don't think that instantaneous speed is calculated as you suggest by distance/time with time = 1 sercond. Velocity is a direct reading from the chipset. Obviously average speed IS calculated by distance/time.


Last edited by M8TJT on Tue Jul 24, 2012 5:10 pm; edited 1 time in total
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lbendlin
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PostPosted: Tue Jul 24, 2012 5:10 pm    Post subject: Reply with quote

The overspeed warning is for the current speed, not the average speed/
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