How to create an HLOD model from a tiled 3D model of a city?

I have a 3D model of a city, that has been created from flight photographs using photogrammetry. I need to convert this model to a hierarchically lodded model suitable for real-time rendering of the city, such that fine/low level details are used to render parts of the model that are close to the camera, and coarse/high level details are used to render parts of the model that are far away from the camera, in order to limit the memory requirements of the application and the time it takes to render each frame but still get descent rendering quality.

The 3D model itself consists of 74*95 adjacent tiles stored as filmbox files and associated jpg texture files, which in total take up almost 100 GB in memory. How can I convert this to a HLOD model in Unreal Engine 4?

It’s also a plus, but not a requirement, if it is possible to load and render the resulting HLOD model in OpenSceneGraph.

You can only HLOD what you can get into a scene. And HLOD wont break up one model into multiple actors, you need to do that manually first.

You’ll probably have to break up the model into individual buildings outside of UE4. Run the model through some sort of polygon reduction (not necessarily to reduce detail, but to make sure all of the geometry is being used as efficiently as possible) and auto UV. Bake over the textures. Repeat for each building.

And then do the same with with chunks of the road (probably about a block).

You might be better off using a specialized application for working with photogrammetry data.