Methods and apparatus are described and illustrated for producing GPS
corrections, comprising: collecting measurements from a plurality of
network reference stations; determining network corrections from the
measurements; determining residual errors at one or more vernier-cell
reference stations; and preparing vernier-cell corrections to compensate
the residual errors within a vernier-cell region. Network correction
streams are described and illustrated which contain network corrections
derived from a plurality of network reference stations and residual error
corrections derived from one or more vernier-cell reference stations.
Methods and apparatus are described for employing such network correction
streams in a virtual reference station to produce corrections and/or
virtual measurements for use in a GPS receiver.
