Here's a question, why couldn't GTS have dynamic time of day and weather? Was it due to the PS4's hardware constraints?
Full disclosure: I am not a programmer, nor an environment artist, or a lighting artist - this is just what I know from things I’ve picked up on over time from various sources.
If GTS had dynamic time of day and probably weather, the game would’ve looked noticeably worse. This is because GT Sport uses baked lighting (ray traced at that), which is a visual step up from dynamic lighting, but is always static. This is the same reason that helps The Last of Us Part II look so good - all the lighting is baked. I don’t think baked lighting is a bad thing, it just depends on the game.
For TLOU and games like it, where TOD doesn’t really influence anything, gameplay wise (whereas races can take place from day through the night IRL), baked lighting is probably the way to go, if you’re not aiming for a dynamic system. The visual fidelity it has along with more resources for other parts of the game really helps if you’re trying to push the envelope, graphically. There’s no way you could run real-time ray-traced global illumination on the PS4 with a game of such complexity and fidelity (GTS or TLOU II, or pretty much any last-gen AAA game out there), not unless you drop the resolution dramatically and even then, it would run pretty poorly.
I believe that’s partly why GTS’ file size is so large, due to all of the light maps.
Here’s an article on GTP from a few years back which goes in depth about the lighting system:
https://www.gtplanet.net/polyphony-digital-reveals-gt-sports-iris-ray-tracing-system-at-cedec-2018/
EDIT: Having said that, I believe Horizon interpolated between “sets” of baked lighting for their time of day, if I recall correctly, so perhaps something like that could’ve worked for GTS? I’m not 100% though, I might be misremembering.
EDIT 2: They did interpolate between sets of baked lighting.
"For our indirect lighting solution, we used irradiance volumes. You can think of them as multilayered lightmaps, where each pixel of each layer has a 3D location in space, and multiple directions based on probe positions. We used this for both our static and dynamic objects, giving us a fully unified way of doing indirect lighting for all objects...
It also allowed us to have a dynamic time of day. We baked the indirect lighting of our sunlight at 4 times of our day/night cycle, to 4 different sets of irradiance volume textures, which we then blended overtime to give the illusion of having accurate indirect lighting across all times of the day."
https://www.resetera.com/threads/gu...cimas-lighting-and-render-systems-work.54431/
Having said that, I did notice that the interpolation did feel a bit... fast? A little unnatural. I wonder if this was because the lighting was baked four times. Not sure if it was a hardware limitation or just an artistic choice, but perhaps a few more “sets” would’ve made it look a little more natural. Definitely wasn’t bad, it was fine, just something I was thinking as I played.