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An estimate of the position accuracy from the Global Navigation Satellite System (GNSS) can be derived from several factors, including:
  • A
    Geometric Dilution Of Precision (GDOP) and User Equivalent Range Error (UERE).
  • B
    The correction for the receiver clock error as transmitted by a differential station.
  • C
    Inaccuracies from the geometry of the satellites above the user's horizon.
  • D
    User Equivalent Range Error (UERE) alone.

The User Equivalent Range Error (UERE) is the maximum position error that has to be expected by the user and can be calculated as the square root of the sum of all individual errors squared (ionospheric propagation delay, satellite clock error, satellite orbital variations, multipath propagation). UERE is therefore the value of all residual errors affecting the receiver position after attempts have been made to compensate.

The actual position error to be expected is however not only affected by UERE. Another factor is the Geometric Dilution of Position (GDOP).
The total position error can be computed by multiplying UERE by GDOP.

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