Accuracy and Precision

Accuracy and Precision

Accurate results may not be precise and precise results may not be accurate

• Accuracy = how close is the measurement to the actual value, can only be calculated if the ground truth is known
• Precision = how close is the measurement to other measurements, might be high even though some systematic error cause all measurements to be off

The receiver can measure the received signal ­strength, through the so-­called carrier­-to-­noise-­density ratio \(C/N_0\), which gives an indication of the quality of the measurement (larger signal­ strength yields more precise measurement).

The pseudorange measurement precision is typically at the one or few meter level for low­-cost, mass-­market equipment, and can get down to the few decimeter level for professional high­end equipment.

The carrier phase measurement precision ranges from the few centimeter to the millimeter level. The carrier phase is an ambiguous measurement of distance, but it is more precise than the pseudorange, typically by two orders of magnitude.