Say you want to create a 3D game, and have either players, or mobiles, be able to tract other entity by following their scent trails. Is there any known data-structure that matches this use case?

If you have only few individuals going about, you can probably do something like a map of 3D coord to entity ID, but real scent works differently, because it fades over time, but slowly. And most of the time, you can only know approximately what went there, and approximately how many things of that type went there. And the approximation becomes worst with time, until it's gone.

I imagine it's kind of like starting with an exact number, and slowly loosing the least significant digits, until you loose the most significant digit too. But that doesn't really help me, because entity IDs aren't normally encoded to contain the entity type, in addition to it's individual ID.