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GPS accuracy
Started by richard11 Sep 11 2018 07:15 AM

10 replies to this topic
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#1

richard11

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Currently putting a proposal together for a new client, on the development of a mobile app which will be used in woodlands. Long story short, the primary purpose is to record and upload data but of course, in a woodland, there's limited connectivity.

 

Most of the data recorded is manually input, or relies on device sensors that will work offline no problem, so for the most part we'd simply store the data locally and upload when there's a connection, no problem at all.

 

BUT one crucial element will be obtaining the lat/lon value of where the device is at the time this data is recorded. I'm aware that GPS is completely independent of data connectivity, but given both GPS and mobile data connections are essentially the same in terms of being satellite based technologies, I'm wondering if there's just as much chance of being offline from a GPS perspective as from an Internet perspective. I.e. if the signal drops, is GPS going to drop too?

 

Does anybody have any experience with this? The sat-nav in my car has never had issues tracking my location and I don't recall sat-nav on Android struggling either, so long as the maps are pre-fetched and a route doesn't need recalculating mid-journey, but of course I've never driven through a dense woodland!



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#2

Rob Miracle

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GPS needs to see at least three satellites in the cluster to work. The more satellites your device can see the more accurate the results will be. If you're outdoors, you shouldn't have any issues getting GPS data (note there will always be some inaccuracy for security reasons). If the person carrying the device crawls into a cave for shelter, or the forest cover is quite heavy, you might lose signal for a little bit.

 

The biggest issue is being indoors. It doesn't take a lot of building structure to block enough signal to lose GPS data.

 

Rob



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#3

richard11

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Thanks Rob, that makes sense.

I'd forgotten when posting this but another dev reminded me that a regular data signal bounces off of masts rather than directly communicating with the satellites, so that's more susceptable to signal loss. This combined with your feedback I think gives me enough confidence in our approach here =)

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#4

agramonte

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Sounds like a fun project. My experience with old-school GPS devices is that outdoors you should not have a problem. 



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#5

richard11

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It'll be the first app we've used Corona for instead of building native or as a Phonegap project, so it'll be an interesting one. Corona supports all of the necessary sensor events and networking though so I don't see any reason not to use it, despite its focus on games. I'll definitely post a link back here when it launches. I can't give anything away about what it'll do just yet though as it's the first of its kind and will form the basis of our clients new business - don't want to risk anybody taking the idea and beating us to the finish line...

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#6

XeduR @Spyric

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From what I remember from an old GPS based project of mine (not made with Corona), the GPS does work even if the device has no connection, but the accuracy of the location seemed to significantly improve when Internet connection was used. I can't verify if this was due to the Internet connection itself, or if it meant that the device simply had a better signal and could therefore receive more accurate location.

 

The most important factor regarding location accuracy seemed to be the quality of the receiver (i.e. the device and its parts).



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#7

Rob Miracle

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Location services will use WiFi hotspots to supplement the GPS or provide location data to devices without GPS chips. Your device will generally determine it's location quicker from WiFi since it takes time to acquire the GPS constellation. This is why when you bring up a map application you see a large blue circle and it eventually shrinks to a smaller circle with the more accurate GPS signal.

 

Having both WiFi and GPS data will supposedly provide more accuracy.

 

Rob



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#8

agramonte

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Everything Rob said is correct. GPS does not need internet service to connect but on phones it helps.

 

@XeduR depending on how long ago you worked on that app, accuracy has improved. Prior to the year 2000 the USA would intentionally lower accuracy for civilian applications. It is not the case anymore.

 

@richard11  I think I read somewhere that some phones accuracy is more than 12 feet radius. Depending on the application that might not be acceptable. Compare that with some dedicated GPS (CPGPS) that have accuracy of a few cm. 

 

Without wifi most phones will take longer to acquire the satellite signal. I don't know the exact reason but it has to do with the phone connected to Wifi being able to prefetch a satellite location data (ELO or EMO) that otherwise it will have to determine once it has acquired enough satellites.



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#9

richard11

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Accuracy shouldn't be massively important to this particular application, just so long as something reasonable can be obtained. Basically, if you can stand where the GPS claims you were and see the point you actually recorded, that'll do just fine.

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#10

davida6

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The gps also uses the cellular data - triangulating from the towers. One problem you will run into using FINE accuracy is generation of 0 value records if the provider switches from the chip set to WiFi or Cellular. I’ve found that this works better (fewer 0 records) if COURSE accuracy is turned on when heavily depending on WIFI and CELLULAR.

A bigger issue (for Android) is google’s handling of presenting gps data through google play services. To better manage battery life, they have dramatically reduced the frequency of presenting gps data. A quick search on location services changes for Oreo will explain it all.

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#11

richard11

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Thanks for the pointers. When we come to development I may very well need to read up on this in more detail!


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