Accurate GPS positioning has been of interest in automating data collection in field strength surveys of antennas on HF. To be useful, the positions need to be accurate to 100mm.
RTKLIB is an open source program package for GNSS positioning.
A number of experiments were conducted using a U-Blox LEA-6T assembly with integral small patch antenna (cost ~A$40) and RTKLIB v2.4.3(b8) using a base station feed from Geoscience Australia (with thanks). The test location is about 200km from the reference station at Symonston ACT.
Above, the LEA-6T and a RS-232 to USB adapter are strapped to a roof rack bar with stretch film. The high mounting position gives good view of the sky.
Above is a position plot of about an hour with the vehicle stationary (though in Kinematic mode) beside the house. Sky view was slightly restricted by the house and a line of tall trees to the west.
For the most part the track is smooth, but there is one section where the track in a more heavily treed section is markedly jaggy.