3d car models

I've seen some 3d car models who look exactly like the real thing? How do they make this in autocad? Where do they get the dimensions?

Dimensions-Probably from the manufacturers and designers themselves

Autocad- Autocad can do it but with a lot of limitations, usually for cars there's Mechanical and Solidworks that specialize in designing em, im not aware of any other software that they use

it probably is the manufacturer but i dont understand how they get leaked to the public, theres a big problem in the luxury/sports car market with people creating replica panels and fitting them to a much lesser car:? (ooh noo im now officially a very boring person)