Resolution of less than 1 meter is normal with a decent view of the sky and a lack of interference. GPS itself is always receive-only on our end as consumers.
What problem are we trying to solve here? At this point in time, guided navigation with completely offline maps and GPS has already been a no-brainer off-the-shelf thing for decades.
> GPS itself is always receive-only on our end as consumers.
AFAIK it's almost always enhanced by things cell tower data, wifi network data, and external data sources (besides the satellites). Look up GPS/GNSS enhancement and augmentation for the latter.