Systems, devices and methods are provided improving the accuracy,
availability and integrity of GPS service. Specifically, the present
invention provides a GPS device with the correction messages which are
from the most accurate and desirable source while at the same time
conserving processor and memory resources of the device. The method
includes receiving GPS data. An SBAS signal from a first correction source
is received. Ionospheric mask messages, for a number of grid points, in
the received SBAS signal are analyzed. An abbreviated bounding region
around a group of similar type grid points is constructed. The method
further includes determining whether the position of the GPS device is
within the abbreviated bounding region.
