HI King Coffee
I think you’re over thinking this.
It sounds like you’re opening the OBJ in a text editor,. no need.
First,.. You make a model,. such as a cube,. then you would apply a “preset” UV mapping type to that model, EG: (Box mapping) and select an appropriate “layout” option,...
You can define a “custom” UV Mapping type, EG:( define seams and pins manually,. and use Unwrapping)
Once you’ve applied a “UV Mapping type”,. then your 3D program will know “How to” project the 2D texture maps,.. onto the 3D model.
When you make a 3D model,. and you want to apply a texture to that object, then there are two basic ways..
You can create a “Procedural shader”,. which uses colours, and math’s to apply a texture to the object,. (this doesn’t require any UV mapping)
You can also use 2D images (Texture maps) and apply those to the 3D model,. In this case you DO need to specify how the texture map should be applied to the 3D object.,, and that’s done using UV mapping.
The vertex editor has a UV mapping area,. where you can specify and change the mapping type.
You can also apply different layout options from the “operations” tab
When you apply a UVW mapping type to a 3D object,.
The Objects is split “virtually” and then flattened out into a 2D wire-frame (UV Grid area),.
This is then matched with the 2D layout of your “Texture map”.
In a 3D object,,. the vertices are numbered and have values to specify their 3D position,. (X, Y, Z)
In a 2D image,. values are normally represented with X, and Y.
In a 3D program,... (to avoid confusion) the 2D mapping reference used is UVW (or UV for short),. while the 3D model reference is XYZ
Hope it helps