RTXDI vs RTXGI and how they both work with Lumen

It is difficult, especially for any new developer, to get heir heads around RTXGI vs RTXDI, their purpose, and how they either replace or complement Lumen.
From my understanding of Lumen, doesn’t it do exactly what RTXDI +RTXGI does?
For example Richard shares an amusement park, ferris wheel scene at the 31 minute mark and suggests this is a great example of combining Lumen with RTXDI. But where does RTXGI fit in then?

I also watched this excellent presentation from 2021 GDC

Some type of simple comparison flow chart listing features and advantages, hardware requirements and most importantly, the ways in which RTXDI+RTXGI complement Lumen, would be HUGELY useful!

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I really think that RTXGI was there before lumen, back for UE 4.27.
It’s a different tech than what Epic did. There’s a lot of GI solutions (remember Light Propagation Volumes ?)

So… my understanding is that RTXGI does overlap with Lumen, but has the advantage of using Nvidia-specific accelerations.

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Yeah. Similar to Lumen I believe it also relies on radiance caching.
Need to do a test comparison of

  1. Lumen alone with Hardware RT enabled
  2. Lumen + RTXDI
  3. RTXDI (Lumen off)