FlightTest
The vertical path used in VNAV, whether VNAV or VGP, is based on the two lateral waypoints and the barometric altitudes, hence "Baro-VNAV". At colder than ISA temps the path will be shallower than at ISA, conversely at higher than ISA temps. This is because the true altitude at the first waypoint will be, in cold temps, lower than standard by a greater deviation than the lower waypoint i.e. the runway. All paths based on Baro-VNAV will have temp limits which must be observed unless the FMS has temp compensation.
Raw GPS fixes are not presently using GPS heights unless augmented with WAAS creating a LPV glide slope.
GF