VTEC map generation to support ionospheric error models for satellite-based navigation

These are the associated Matlab files corresponding to the ionospheric model proposed in M. Imad et al., "Ionospheric error models for satellite-based navigation-paving the road towards LEO-PNT solutions", submitted to MDPI Computers. The main code in this file is a simplified version of the code used in the simulations that were discusses in the paper, but it uses the Y matrix that was presented in M. Imad et al. (2023) to generate TEC values corresponding to random users. The Vertical Total Electron Content (VTEC) map has been saved in TEC_HourMap.mat. The Main.m function shows an example with 10 users uniformly distributed on Earth and the VTEC values corresponding to them (i.e., VTEC values from the user position on the ground until 450km above the Earth). The actual ionopsheric delays depend on the Slant TEC (STEC), which can be derived from VTEC and from the actual satellite constellation (STEC tells us how many electrons 'collide' with the satellite signal when the signal crosses the ionopsheric layer). The VTEC however is independent on the satellite constellation as it only shows how many electrons are present above a certain location (lat,long). The files are distributed under CC4_BY license.