Dilution of precision metrics are common in GPS applications. The horizontal dilution of precision comes directly from the Cartesian components (x and y) of the position estimate covariance matrix in equation (20).
The HDOP metric is normalized by the range uncertainty (ffr)to isolate the sensitivity of the metric to the solutions geometry. Fig. 7 illustrates how this Cartesian interpretation overestimates the uncertainty by describing a rectangular boundary of uncertainty ellipse.
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