Dual XGPS160

Discussion related to external and internal GPS / GLONASS / Galileo / BeiDou sensors
gplracerx
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Re: Dual XGPS160

Post by gplracerx »

What it says in the GPS display and what HLT actually uses in the end are not the same. I have a VBOX Sport that updates at 20Hz. In the GPS page it shows connected at 20 Hz. But when you look at the actual data file, it says VBOX Sport @ 10Hz because only about half the fixes are logged.
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bulls23
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Re: Dual XGPS160

Post by bulls23 »

I think that's because of the data compression. You can turn it off in settings but that will generate bigger logs. At first glance, we definitely want as much fixes as possible, but that can lead to some poor reaction times while analyzing the data. Laps of the Nordschleife at 20Hz are that big, so even an iPhone 5 struggles while processing the data.
Which file type are you talking about btw? Haven't tried if the compression setting has an effect on VBO files yet, but the 10Hz could also be declared in the file for compatibility reasons with Circuit Tools. Anything below that value would lead to crashes in the past.
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Re: Dual XGPS160

Post by gplracerx »

It's right there in the device. Go to Lap List. Select a lap. Below the preview screen under Data Recording you will see a 'GPS Sensor' line. In my case it says: External @ 10Hz. I have compression turned off. What's the point of a high data rate GPS if you throw out most of the data? I might as well go back to the Emprum.
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Harry
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Re: Dual XGPS160

Post by Harry »

gplracerx wrote:It's right there in the device. Go to Lap List. Select a lap. Below the preview screen under Data Recording you will see a 'GPS Sensor' line. In my case it says: External @ 10Hz. I have compression turned off. What's the point of a high data rate GPS if you throw out most of the data? I might as well go back to the Emprum.
DeWitt, I wonder a little bit about the discussion as I provided you with a in depth information on the background of the 10 Hz display. In fact LapTimer makes a guess on the update rate by using the time gap between fixes that appears most often in the recording. Your sample showed 125 fixes updated at 10 Hz and 95 fixes updated at 20 Hz - which makes a 10 Hz display currently. Please feel free to turn off compression, it is available as a setting in LapTimer. In general, LapTimer stores every GPS fix it receives. Finally, your statement throwing away fixes makes no sense, is not true. In case it does not provide any additional information and can be recalculated by interpolation - it is certainly valid to remove it. Keeping it just to show an update rate the sensor formally delivered makes no sense from my point of view. But as written above, if you do not like that behavior, please just turn compression off.

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gplracerx
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Re: Dual XGPS160

Post by gplracerx »

Compression is off on my iPod as I stated above. I have no problem with the actual as opposed to theoretical update rate. I was just pointing that there was a difference. I would be very interested to see how close the actual rate of the XGPS160 was to it's maximum rate. That might make a difference to people considering which external GPS device to purchase in the future.

The higher the data rate, the more accurate the calculation of acceleration from the measured velocity will be and the less information that will be lost by the necessary smoothing of the calculated acceleration data. You can't do that by removing points and then interpolating to put them back. You need the actual data. You can't get information on frequencies more than half the actual data sampling rate. Presumably there is internal filtering in the GPS device to prevent aliasing of higher frequencies.
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Re: Dual XGPS160

Post by Dr_Pippin »

Just saw the XGPS160's FAQ page: http://gps.dualav.com/faq/xgps160/
Will the XGPS160 work with racing apps like Harry's Lap Timer or TrackAddict?

Yes.
HLT getting some love from Dual!
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Re: Dual XGPS160

Post by gplracerx »

I've obtained a Dual XGPS160. It seems to work fine with HLT and with iOS Location Services. One important advantage over some other external GPS devices is that the XGPS160 can receive signals from the Russian GLONASS system as well. With the other devices I've tested, I've never seen more than 10 satellites. The XGPS160 had 16 in view the first time I used it. The only problem I can see so far is that the non-slip mat may be a problem in competition. It might be OK for an autocross, but definitely not for a race car where a positive attachment to the vehicle is required. I haven't looked very hard for a positive mount for the Dual. I was getting 9Hz for the Dual and 5Hz for a BT1 connected at the same time. Unless you absolutely positively have to have 20Hz data logging capability or a positive mounting system, the Dual seems to be a better deal than the VBOX Sport.
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Re: Dual XGPS160

Post by Harry »

Can you please check which NMEA sentences appear in the Satellites View or the XGPS entry in Sensor List? Thanks.

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Re: Dual XGPS160

Post by gplracerx »

GLGSV, GPRMC, GPGGA, GNGSA
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Harry
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Re: Dual XGPS160

Post by Harry »

Interesting. The latest NMEA standards 3 says:“GP”: GPS; “GL”: GLONASS; “GN”: GPS+GLONASS
This means GSV is a GLONASS sentence, RMC and GGA come from GPS, and GSA is a combined sentence.
  • GSV is the satellite details information shown in LapTimer's Satellites View
  • RMC is the basic set of position data
  • GGA has some additional position data
  • GSA includes the satellites currently used for position calculation, numbers 1-32 are from GPS, and 65-96 are GLONASS
Would be interesting to understand how and if GLONASS information goes into position information here...

- Harry
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