>>28406
You still fail to describe what exactly you want, for the sake of the thread I'll talk about both 3 and 2D and what I think youmight be talking about .
Here's 3D:
It depends if you mean like snapping segments of geometry (complex structures like rails) or simpler, more organic patterned materials like dirt or stone.
For the small stuff there is voxel technologies I'm not at all familiar with or aware of how much they're integrated into most of the popular middleware. It ranges from minecrap-tier all the way to stuff like this:
https://www.youtube.com/watch?v=mcpLSHU8M1c
For 3D objects snapping together you can either use a 3D grid to organize them, so they always align... OR you can script them in such a way they snap onto bones (the same one uses for rigging) of the previously placed objects. There are likely some kind of built in tools for this in most graphics engines. Think about a rifle snapping to an npc's hand. I'm sure some other anons can tell you all about it.
You can repurpose those to do what you want with larger, static objects.
2D: simple shit, you take a 3D model, slash it up into a vertical-facing grid. You render these portions of the structures you want to piece together in the game into 2D sprites, deploy as identically sized tiles on the map's grid.
With some basic bitch scripting you can add border tiles to be generated between different types of flat terrain tiles... I dunno if roller coaster tycoon had anything more to it than this.