On Firefox, Edge:
Hit ‘F12’ → Debugger → resize the developer tools upwards for your convenience.
Under ‘modelvviewer.dev’ on the left browse the folders for the relevant source files and see the code on the right panel.
(On Opera Ctrl + Shift + I).
You can also download the gltf model viewer (I don’t think it’s the same):
Click on “Code” on the right, download “.zip” and extract.
No the model viewer is not the same, I am only interested in the logic of how they are hiding and showing the markers.
Where exactly should I search for this, I mean what URL, do you mean here?
I tried to use their npm as described but there are a lot of errors when building the project and it dose not work…
This is the way to do it but I have no idea how to implement it in code “A faster alternative to what you’re doing now would be to raycast just once for each marker, storing the normal vector of the surface at the intersection. Then show the marker when that normal vector is within some range (maybe 75–80º) of facing the viewer.”
I am searching and searching but no luck 
I have posted this as a paid job, I need to solve this asap, if you guys are interested and think you can help me please let me know.
Ok guys @ XAR actually wrote the code for this using the “storing the normal vector of the surface at the intersection” unfortunately is not usable some markers are acceptable but others do now work, can this be improved?
