Q:

HoloLens external rendering

Does soneone of you have a good solution for external rendering for Microsoft HoloLens Apps? Specified: Is it possible to let my laptop render an amount of 3D objects that is too much for the HoloLens GPU and then display them with the HoloLens by wifi including the spatial mapping and interaction?

A:

It's possible to render remotely both directly from the unity editor and from a built application.
While neither achieves your goal of a "good solution" they both allow very intensive applications to at least run at all.
This walks you through how to add it to an app you're building.
https://docs.microsoft.com/en-us/windows/mixed-reality/add-holographic-remoting
This is for running directly from the editor:
https://blogs.unity3d.com/2018/05/30/create-enhanced-3d-visuals-with-holographic-emulation-in-uwp/

