I would not call the first method physically based since it does not even trace the path of photons.
Physically based doesn't mean physically accurate, just that it is based on real physics (unlike, e.g. Phong shading, which was based on intuition, or the standard implementation of Blinn-Phong which is based on a solid theoretical foundation but blatantly violates the conservation of energy).
However, yes, comparing any PBR technique to the real world lets us measure how correct it is. Or, in games we often compare our PBR renderers to existing film-quality PBR renderers :lol:
PBS is the approximate way to PBR, am i right?
No. Rendering covers the whole system (lighting, geometry, shadows, shading, post processing, etc) whereas shading is just the interaction between lights and materials.
PBS is a small part of PBR.
In (1), it use environment map to do light calculation. And in (2) it use light that we define (just like point light, directional light) to do light calculation.
My question is:
(1) What difference between two method?
(2) In my understanding, (1) do the indirect lighting, (2) do the direct lighting, are they?
(3) If so, do i need both of them in my light calculation? and how to combine them in the final result?
I haven't read your two articles yet, but just to be clear, PBS/PBR are not nouns / they are not a specific thing. PBS/PBR are adjectives that can be used to describe endless things.
Two different games might both say "We do PBR!", but their algorithms/shaders/code are probably completely different from each other, because what they mean is "our renderer uses some algorithms that are based on approximations of physics".
As for combining direct vs indirect lighting - all lighting is additive. Indirect lighting is just another type of light source such as spot, point, directional, etc...
In the real world there is a lot of indirect lighting going on. When you reproduce a real world material using PBS, but only light it with direct lights (point, spot, etc) they tend to look very wrong, as this lighting situation is unrealistic... So once you have PBS, figuring out a way to do more and more PBR (such as indirect lighting) becomes important.
There is no one standard implementation of PBS, but the most common techniques at the moment are covered in the Unreal 4 rendering course notes by Brian Karis.