Ultimate GPS precission at low speeds

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jorge5a
 
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Ultimate GPS precission at low speeds

Post by jorge5a »

Hi!

I am making a GPS localitation system using Ultimate GPS. I have about 10 of it, all with same hardware (Arduino + Ultimate GPS).
The system works fine if the object where I have attached is in movement, but if the speed is slow, about 0,5 Km/h the GPS starts to be not precisse with errors up 150 meters.
With the same hardware I have 2 that works perfect..
Someone had similar problem? or know a solution for it?

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adafruit_support_rick
 
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Re: Ultimate GPS precission at low speeds

Post by adafruit_support_rick »

Please refer to page 13 of the command document. You can set the nav speed threshold ($PMTK397) for low-speed applications:
http://www.adafruit.com/datasheets/PMTK_A08.pdf

Also, see this thread:
http://forums.adafruit.com/viewtopic.ph ... ld#p279903

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jorge5a
 
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Re: Ultimate GPS precission at low speeds

Post by jorge5a »

Dear admi:

I have this sentence at top of my code
$PMTK397,0.00*0D. But I have tested other same GPS and by default is with 0 (low speed)
It's possible I have Other Ultimates GPS with other configuration Threshold by default?

Thanks

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adafruit_support_rick
 
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Re: Ultimate GPS precission at low speeds

Post by adafruit_support_rick »

I would use the sentence exactly as specified in the user guide:
$PMTK397,0*23

However, if you think the threshold really is turned off, then you are at the limit of resolution of the GPS module itself.

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jorge5a
 
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Re: Ultimate GPS precission at low speeds

Post by jorge5a »

I have tested with $PMTK397,0*23 and I have error, about more 50 meters.
I must send any sentence (like +++) for put on command mode before send the $PMTK397,0*23 sentence?
The GPS is exactly when is stoped and about 3 hour after start, but with more time the GPS lost precision. The system run about 0,03 m/s
Do you have any idea, about I'm doing bad?
I must add or change another chip variable?
The same systems works fine in other places. The precission changes depending the place where the system is. But, I have ever good connection satellites, about 7-11 satellites.
Thanks a lot

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adafruit_support_rick
 
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Re: Ultimate GPS precission at low speeds

Post by adafruit_support_rick »

jorge5a wrote:I must send any sentence (like +++) for put on command mode before send the $PMTK397,0*23 sentence?
No. Just send the $PMTK sentence.

I think you're just at the limit of accuracy of the system.

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Barry914
 
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Re: Ultimate GPS precission at low speeds

Post by Barry914 »

Do you have WAAS enabled? There's a dramatic improvement in stability when I have it enabled.

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jorge5a
 
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Re: Ultimate GPS precission at low speeds

Post by jorge5a »

If is not for default I have not it active.
Could you advice me what option to select with DGPS?
0’ = No DGPS source
‘1’ = RTCM
‘2’ = WAAS
And will be better activate or not SBAS?

Thanks a lot

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adafruit_support_rick
 
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Re: Ultimate GPS precission at low speeds

Post by adafruit_support_rick »

Which DGPS you activate depends on where in the world you are.
In North America, activate WAAS.
You want to activate SBAS.

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jorge5a
 
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Re: Ultimate GPS precission at low speeds

Post by jorge5a »

SOLVED!

Thanks a lot, I was using Arduino with SoftSerial library to chat with the GPS.
I have changed the sentence and all works fine :)
ss.wite("ss.println("$PMTK397,0*23\r\n")") -> Didn't work form
ss.println("$PMTK397,0*23")- > works fine

The mistake was ever on the threshold. The GPS module is perfect!

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