Internal GPS accuracy

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11-09-2016 02:17 PM
RandyBurton
MVP Regular Contributor

In the GPS receiver support document it states: "Estimated accuracy is not available for internal GPS systems on devices."  However when using the internal GPS, these fields (Horizontal Accuracy and Vertical Accuracy) do contain data.  Is it that the data is inaccurate?  If so, what other data from the internal GPS should be considered inaccurate or suspect?

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4 Replies
GISSupport3
Regular Contributor

How accurate can a GPS in a mobile phone? 

Sure to be other articles around as well.

JayRiester1
New Contributor III

Here is another article about Cell Phone Accuracy vs Professional GPS Accuracy.

https://www.linkedin.com/pulse/how-accurate-your-smartphone-ken-joyce

Step 1: It does come down to Precision vs Accuracy and Repeatability.

One of the major issues with Cell Phone/Tablet only accuracy, is to know where your positional accuracy is truly coming from: GNSS Only, GNSS with SBAS, Cell Tower, and Wireless Router.  Or a combination of any of the four listed.

Step 2: What are the levels of accuracy that your software on the Cell Phone/Tablet can handle via filter settings, display and recording of the data and GNSS Metadata.

Step 3: Once you get into higher accuracy receivers (Sub Meter, Sub Foot or Centimeter) then you need to consider the following. Coordinate Systems, Projections, Datums, Geoids, Real-time Correction Service and its Coordinate System and Datum.  All of these raise a whole different level of accuracy parameters in the equation of overall GNSS Accuracy.

Step 4: Always test and verify via multiple control points in your work area as a "Best Practice". This can be done by locating local certified NGS control points.  See our recent blog on NGS Control - Resources to finding them: http://mapsupport.seilerinst.com/2016/10/31/ngs-control-points-resources-to-finding-them/

Jay

RandyBurton
MVP Regular Contributor

The information about internal GPS accuracy is helpful.  But the documentation indicates that for internal GPS accuracy is not available, yet data is being placed in the accuracy fields.  I would expect that it is coming from the internal GPS, but could this data just be bogus numbers from some incomplete math calculation?

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Kylie
by Esri Regular Contributor
Esri Regular Contributor

Hi Randy -- thanks for calling my attention to this. The wording in that topic was unclear, and it has been updated. The sentence "Estimated accuracy is not available for internal GPS systems on devices." was about estimated accuracy: internal GPS does report accuracy, and that is what you are seeing in your data. Where that accuracy comes from depends on your device:

  • If you are using an Android device with an internal GPS that outputs valid NMEA and there is a GST sentence, the GST sentence is used by Collector to record the accuracy. This uses root mean square (RMS) accuracy.
  • If you are using an Android device with an internal GPS that outputs valid NMEA and there is no GST, but a GSA sentence, then the accuracy you are seeing reported is estimated accuracy. 
  • If you are using an internal GPS that doesn't output NMEA, or that is outputting invalid NMEA, the accuracy you are seeing is that reported by the device's location service. In this scenario, the way the accuracy is calculated is based on your device, and won't follow the formula for estimated accuracy that is outlined in that topic.

If you tap on the Location Accuracy badge on the map, you'll see details of the accuracy you are currently getting. If it is based on GST, you'll see "(RMS)" after the number. If it is estimated, you'll see "(Est.)" after the number. If it is using the device's location service, it can be RMS (some Android devices without NMEA do report accuracy that same way).