I have been using Noesis World Space UI for scenarios which combine 2D and 3D. The World Space UI is either in a fixed 3D position or shown via billboarding.

I saw this screenshot the other day, and I was curious if anyone has thoughts on how they might be integrating Noesis 2D line drawing with 3D rendering -- where a height component is involved.

It looks great. Is it a Noesis View rendered to a texture, with said texture applied to the terrain?

That screenshots is from Age of Wonders 4 from Triumph Studios.

Developers use the forums sometimes, let's see if they provide more information about this.

They have customized NoesisGUI in several ways, but I am not entirely sure those lines are rendered with Noesis.