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3. How accurate is the app?

How accurate is the app?

A quick reminder that MilGPS is intended for navigation use only - applications that require precise positioning (eg surveying) need special software and hardware designed for that purpose.

Short Answer

When using the WGS84 datum, MilGPS will be as accurate as the GPS receiver in your phone. Typically 5m horizontal accuracy can be achieved with a clear view of the sky. When using a datum other than WGS84, the accuracy of displayed locations will depend on both the accuracy of the current location fix and the accuracy of the datum conversion. In general datum conversions introduce an additional 5-25m of inaccuracy.

More Info

Consider where inaccuracy may be introduced in an app:

• GPS error. This is the accuracy of the GPS receiver’s current location fix. It is influenced primarily by signal strength and the number of satellites visible to the receiver at any one time. The location fix is provided by iOS. All apps will be subject to GPS receiver error. This is the “accuracy” value shown in MilGPS.
• Conversion error. Most apps will use a well-tested conversion library for their coordinate and datum conversions. Some apps (including MilGPS) use GeographicLib and Proj.4, other apps use GEOTRANS. When using the WGS84 datum, conversions between location formats do not introduce substantial additional inaccuracy (eg conversion from WGS84 lat/lon to WGS84 MGRS). When using datums other than WGS84, up to 5-25m of inaccuracy may be added. This varies with the datum used, and with your current location within the datum’s valid region. This additional inaccuracy is not reflected in the accuracy shown in the app which refers only to the accuracy of the current GPS fix.