Oh, neat!
I didn't realise that there were a research thread for Gran Turismo Concept aswell.
Great finds
@Castrol96. The dirt layout that is reminiscent of Tsukuba Circuit is rather questionable indeed. Its plausible that Polyphony Digital created the circuit using the original model of Tsukuba Circuit, before editing it accordingly. Given the name and the exceptional amount of elevation alterations and jumps, it appears to be, as the name somewhat implies, a track used for testing purposes.
The early build of Twin Ring Motegi is rather reminiscent of the early Nurburgring build in the Prius Trial Version, as both highlight the early modelling processes of the circuits of Gran Turismo. This, as we've seen, typically involves creating a floating layout before adding anything that could be regarded as the surrounding environment.
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Speaking of Gran Turismo Concept. I recently acquired this:
Came with free complimentary considerably scrunched Japanese newspaper packaging.