Logging of GPS positions

General Help and support for the Taranis Radio.
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Raythegreat
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Logging of GPS positions

Post by Raythegreat »

Hi,

I have Taranis With V2.1.9, and FrSky GPS V2. It works very well.
However, I have noticed that when I log all my telemetry sensors including the GPS values and then use Google earth, I lose a few seconds at the end of the flight.
The logging is activated ON by a switch just before takeoff and put OFF after the plane has landed and completely immobilized.

So my problem is when I look into Google earth all the flight is well recorded but it seems there is always the a few seconds at the end that are lost.
This might be a big problem if the plane crashes in the corn field and I want to locate it with the last GPS position.

Is there any reasons why the logging would stop a few seconds before flipping OFF the logging with the switch?

Thanks
RTG

Carbo
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Re: Logging of GPS positions

Post by Carbo »

Raythegreat wrote: Sun Jul 30, 2017 3:29 amIs there any reasons why the logging would stop a few seconds before flipping OFF the logging with the switch?
The FrSky GPS has a noticeable delay. Presumably this is the reason. If you want a fast GPS, switch over to openXsensor.
Raythegreat
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Re: Logging of GPS positions

Post by Raythegreat »

Hi Carbo,

Interesting.

Do you mean the delay is the time between receiving a GPS position and that real GPS position?
Do you have an idea how much time is this delay (in seconds)?
I evaluate this time to be several seconds, approx 5 seconds.
I can see my positions logs stop about 5 seconds before my switch is OFF according to Google Earth.
I clearly see a landing in the corn field just before the landing runway but my plane did a nice landing on the runway.
However, I tested the position of the GPS to be pretty accurate (besides the delay).

What is the openXsensor? Can it be used by X6R receivers from FrSky?

Thanks
RTG
Carbo
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Re: Logging of GPS positions

Post by Carbo »

Raythegreat wrote: Sun Jul 30, 2017 2:26 pm Do you have an idea how much time is this delay (in seconds)?
I have never tried to measure the delay. But if you switch an unused switch when the plane is immobilized (this is visible in the log) and let the log run for several additional seconds you can evaluate the delay.

https://github.com/openXsensor/openXsensor

Additional information about openXsensor and the developer mstrens can be found here: viewforum.php?f=86.
Raythegreat
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Re: Logging of GPS positions

Post by Raythegreat »

Thank you Carbo.

I will try to do some measurements and let you know.

RTG

Raythegreat
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Re: Logging of GPS positions

Post by Raythegreat »

Hi Carbo & All,

I confirm that the FrSky GPS V2 has a significant delay of many seconds.
When I leave the logs ON for 5 seconds after the plane is completely stopped, I can capture the whole flight from Takeoff to the complete landing (plane stopped).

I have not yet find a way to properly measure that delay. I think it must be around 5 seconds which is huge.
any suggestions?

A 5 seconds delay can make a big difference in a crash in a corn field if the battery is disconnected at crash time and GPS did not have the time to transmit the final plane position.

This delay cant represent many meters to identify the crash site.

RTG
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bob195558
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Re: Logging of GPS positions

Post by bob195558 »

Here is some other info about the FrSky GPS V2 (S.Port) sensor: (viewtopic.php?f=97&t=10339&hilit=GPS+V2#p129959).

Bob B.
Er9x on 9x radio, with Smartieparts Programmer and TelemetrEZ Board.
ErSky9x on Taranis, Sky9x, 9Xtreme radios.
3D-Printing: (https://openrcforums.com/forum/viewforum.php?f=129).
Carbo
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Re: Logging of GPS positions

Post by Carbo »

Raythegreat wrote: Thu Aug 03, 2017 1:37 amI have not yet find a way to properly measure that delay. I think it must be around 5 seconds which is huge.
OpenTX logs by default every pilot input, sticks, pots and switches. Just flip an unused switch, when your plane stopped moving. You can see exactly in the log, when you flipped the switch. Let the logviewer display GSpd and GAlt and the switch, to see the delay of both data. You can see additionally in the raw log data (under the graph or open the logfile with a spreadsheet program), when you flipped the switch and how long the GPS position still changed after that, this is your position delay. It is eventually different from speed and alt delay, never tried that. Logging with 5Hz (0.2s) gives a sufficient resolution for things like this.
Raythegreat
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Re: Logging of GPS positions

Post by Raythegreat »

Thanks Carbo,

I understand your method, but you assume that the GPS device is a good and stable sensor.
The Galt, Gspd, Gposition are not stable and not precise even when the plane is stopped, so I cannot measure exactly how many seconds.
I will try this at 0.2 second logging and let you know. I have 0.5 presently. The GPS sends info at each second so logging at 0.2 second might not help a lot.

Thanks
RTG.
Carbo
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Re: Logging of GPS positions

Post by Carbo »

Raythegreat wrote: Thu Aug 03, 2017 1:44 pm The GPS sends info at each second so logging at 0.2 second might not help a lot.
You are right of course. I am used to a 5 Hz update rate from oXs GPS:
5Hz.png
Raythegreat
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Re: Logging of GPS positions

Post by Raythegreat »

Hi Carbo,

I tried with the switch and it does not give me a precise result.
The FrSky GPS is 1Hz and data is not stable when plane is on the ground (Gspd, Galt, lat, long, all move when plane is stopped).
Very difficult to measure the delay. It is approx. 5 seconds.
I will find a way to measure it more precisely but for now I have no solution.

I hope there is no additional delay caused by the Smart port protocol and openTx.


Ray

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