Google explores these techniques as well. They're critical to improving accuracy in urban areas where you don't have line of sight to satellites (this is why your GNSS (AKA GPS) location is terrible whenever you're in a city). Here's [0] a cool gif visualizing the principle of GNSS ray tracing taken from one of Google's blog posts [1]. Here's an article with more information about Google's techniques [2].

[0] https://1.bp.blogspot.com/-FskvGHx-IOc/X8qtZi1GUNI/AAAAAAAAP...

[1] https://android-developers.googleblog.com/2020/12/improving-...

[2] https://insidegnss.com/end-game-for-urban-gnss-googles-use-o...