In this paper, ionospheric VTEC (Vertical Total Electron Content)
estimation methods based on GNSS Regressive models based on spherical
cap harmonic analysis (SCHA) are presented. It is expected that the
spherical cap harmonic function can well model the distribution of the
VTEC in local area like the sky over Japan. The VTEC estimation results
are examined by comparing the precise point positioning (PPP) results
applied by the ionosphere corrections produced from the presented VTEC
model and the Global Ionosphere Maps (GIMs) provided by theInternational GNSS Service (IGS).