Vertical Dilution of Precision (VDOP) (VDOP)

A dimensionless GNSS geometry factor describing how ranging errors are amplified in the vertical component of a position fix.

VDOP depends on the distribution of the satellites used in the solution. Because satellites are normally visible above rather than below the receiver, vertical geometry is often weaker than horizontal geometry and altitude uncertainty may be greater than horizontal position uncertainty.

A lower VDOP generally indicates stronger vertical geometry, but VDOP is not itself an altitude error. Actual accuracy also depends on signal, atmospheric, multipath, receiver and correction errors.