GPS and Speed Accuracy

Variant

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#1
I have the Opia2, and I suppose a suggestion here will absolutely be to check my firmware (which I will)...

With the GPS module, it seems like the speed reported is off -- when I'm going 55, the GPS says I'm going 47 for example. I know speedos in cars are not necessarily accurate, but I fired up Torque on my Android and connected it to my OBD II reader and set up a view for both the OBD speedometer *and* my phone's GPS speed readings. Both are very close...

So I feel like the Opia2 is the one that's off...

Anyone else run into this? I guess I need to hit a speed trap to confirm :)
 
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Variant

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#2
Bumping this...

I've been able to compare against radar as well now and the GPS Mouse is still running quite slow (I think about 15%). Have emailed support to see if they have any ideas.

Opia2 is at latest firmware... maybe I should see if KPH is more accurate?
 

kamkar1

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#3
Your car speedo will always read too much, and i assume its the same speed that come out of the OBD port.
I have tried to compare the GPS in my dashcam ( SG9665GC ) Vs the GPS speedo in the waze like app i run on the phone when driving, and in that case the speed are the same, also related to the radar speed signs we have at some little towns along highways.
But when my GPS speed are 80 my car speedo say 75 km/h.

I cant see the speed on my dashcam as the screen are so little and my eyes so old, so i had to resort calling out the GPS speed from the waze like app and then listen for that during playback of dashcam footage.
And as the phone and camera are the same i always put my car at the speed limit when i pass a mobile speed cam ( we Danes dont have fixed speed cams ) and i have never gotten a speeding ticket.

The GPS are laggin a little if you look at footage where you brake / stop,,, maybe hard, you will see you can almost come to a complete stop before the GPS speed in the footage start to drop.
This i do find a little strange when the GPS used in the cameras are polling the speed many times every second, so to me it should be pretty damn close to a live speed.

I am not sure if having the GPS antenna in a less than favorable place will cause a deterioration in the quality of the speed readings, i have my GPS mouse in the upper left corner of windscreen and the cameras in the middle of it.

Setting KPH or MPH i dont think matter.

Try a GPS speedo app and see what it say, or any other form of app on the phone that give a speed reading too.
If your car have cruise control maybe use that to make sure there are no little speed fluctuations when taking the speed test, at least myself i can fluctuate a little in speed when driving, not least if its in a uneven terrain ( that be as uneven as things get in little old and pretty flat Denmark )
 
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Nigel

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#4
Bumping this...

I've been able to compare against radar as well now and the GPS Mouse is still running quite slow (I think about 15%). Have emailed support to see if they have any ideas.

Opia2 is at latest firmware... maybe I should see if KPH is more accurate?
Sounds like someone is working in Knots instead of MPH - 15% difference. Most GPS units work in knots since GPS was originally developed for nautical and aerospace use.
 

kamkar1

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#5
If that's the case then OP need to buy a old Chrysler as big as a ship, then knots will be good :giggle:

Maybe Vico messed up the knots/MPH conversion, so now it would be really interesting to hear if its the same with KMH,,,,, and i have a sneaky feeling that part of the algorithm are screwed too.
 

Antoeknee

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#7
Hmm, wonder if this is an issue caused by non standard wheel/tyre. Speed shown by my sat navigation is generally 2-4 mph less (speed dependant) than shown by speedo and seems to be same as seen by other sat navigation users. Usually considered more accurate as speedo cannot under read so most manufacturers make over read.
Would expect GPS enabled dash cam to show same
 

lacibaci

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#8
Even when the software is correct in calculating the speed (knots vs mph or km/h) the accuracy will be affected depending on how you drive.
Most dash cams will update speed once a second. This is fine if you drive slow or at a constant speed.
Better devices will sample 10 times per second so this will be more accurate.
 

c4rc4m

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#10
TBH I wouldn't worry if it's under reading. It's all to your advantage.
 
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