How is accuracy calculated?

Suggestions for WiGLE/JiGLE/DiGLE

11 posts • Page 1 of 1

Postby IcAnHaZwIfI » Thu Feb 08, 2024 8:40 pm

I have looked through the java best I can, but was wondering if anyone knows the formulae for calculating accuracy?

Postby arkasha » Thu Feb 08, 2024 11:28 pm

it's provided by the GPS subsystem in Android (or in other providers) as "horizontal dilution of precision" in meters - this raw value is associated with each observation - it's not "calculated" in our system at all.

Postby IcAnHaZwIfI » Fri Feb 09, 2024 1:37 am

So it's merely the HDOP NMEA string? When it says say 73. That's a 73 possible meter area?


Postby arkasha » Fri Feb 09, 2024 4:34 pm

what are you even talking about? you haven't explained:
- where you're seeing this value
- what you're expecting/assuming
- what you're trying to do.

Postby IcAnHaZwIfI » Fri Feb 09, 2024 11:36 pm

On the Wigle app, it showed 73 as the 'accuracy'. I have connected an external GPS unit and have recorded NMEA sentences trying to figure out the accuracy. But using python I have not gotten anywhere near that number.

So is the 73 a representation of meters, accuracy percentage, the HDOP value on a scale of 0 to 100?

Postby arkasha » Fri Feb 09, 2024 11:53 pm

We don't use that string that way anywhere in our UI.

When asking strangers to spend time and effort helping you on the internet, it's common courtesy to be precise and complete when asking your questions.
Please check out the documents for the Android Location core instead of asking open-ended questions.


Postby IcAnHaZwIfI » Sat Feb 10, 2024 12:28 am

I appreciate your time.
If someone doesn't know an answer they don't know how to get to that answer do they?
"How is the accuracy number derived?" seemed fairly direct. But I get your point.

Postby arkasha » Sat Feb 10, 2024 12:37 am

Sure, but you haven't explained where the value you're asking about appears in the app after multiple go-arounds here on the forums, as well as opening a github issue (which is used to track feature requests and bugs, not bug people for info you could get from reading the code).

You literally haven't pointed out on which screen this number is present, and (as I mentioned) we don't say "accuracy" next to any numbers in the UI. You could also expand upon what's got you puzzled here rather than being oblique. is a great presentation from a user on wardirving location accuracy. I'm guessing that what you want to know is something about why Android location is so precise compared to a random GPS - that's probably a combination of terrestrial signals assistance and multiple constellation support, but how would we know?

Postby IcAnHaZwIfI » Sun Feb 11, 2024 3:04 am



As stated I am writing a python script. I plan on uploading to Wigle. How is the requested 'AccuracyMeters' derived?

On the github:
// check if accuracy is under 10 miles
boolean horrible = location.hasAccuracy() && location.getAccuracy() > 16000;
//Great in theory. Real-world testing of GPS accuracy makes this appear impractical
if (currentAccuracyMeters > 10 && currentAccuracyMeters > distanceMeters) {

From the NMEA sentances to the result of 'AccuracyMeters' how is that achieved, derived or calculated?

Postby arkasha » Sun Feb 11, 2024 5:18 pm

You'll have to go read the Android source code - not all Android devices use NMEA GPS signals, but some do.

You can also look at other programs such as Kismet and the jhewitt boards that synthesize CSV uploads.

Postby IcAnHaZwIfI » Sun Feb 11, 2024 9:23 pm

Will do. Thanks.

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