Accuracy XYZ

FAQ for the GNSS-Commander Android app
https://play.google.com/store/apps/deta ... nder&hl=en
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PilaBlu
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Accuracy XYZ

Beitrag von PilaBlu » 16.10.2017, 20:03

The accuracy of your external GNSS antenna is notified by the NMEA-GST string.
nmea-gst.png
nmea-gst.png (15.02 KiB) 490 mal betrachtet
The last 3 values of the GST-string define the standard deviation error for latitude, longitude and altitude.
The GNGST sample in the screenshot above shows: dev-lat=0.330m dev-long=0.217m and dev-alt=0.558m

The position/horizontal accuracy (XY) is calculated by very simple mathematics.
It's the square root of the square sum of the deviation latitude error and deviation longitude error.
In this example: Accuracy.XY = sqrt(0.330^2 + 0.217^2) ~ 0,39m
deviation.png
deviation.png (30.08 KiB) 490 mal betrachtet

If your external GNSS antenna doesn't send the GST string :( the GNSS-Commander app can't display the accuracy!
But on almost all external antennas (U-Blox, Prolific, etc.) the GST-string can be activated by device configuration.

:!: If the internal GPS is selected as current data source we never receive the GST string.
There is no GST string send by the internal GPS, so the accuracy is requested right by the Google Location API.
:arrow: see method https://developer.android.com/reference ... etAccuracy for further information

Google Developers API:
We define horizontal accuracy as the radius of 68% confidence. In other words, if you draw a circle centered at this location's latitude and longitude, and with a radius equal to the accuracy, then there is a 68% probability that the true location is inside the circle.
There is no vertical accuracy (Z) provided by the Location API.
A pretty good estimated value for the vertical accuracy is 1.5 times the value of horizontal accuracy. (that's displayed by GNSS-Commander)

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