Anchoring Areas

[cfalcon]

Is there an official way to do this? What do you guys do?


If you are in a mundane dungeon, or a forest, or on the road, or wherever, it's pretty obvious how spell areas work. If you put down a Silent Image with 6 10-foot cubes by the side of the road, it's pretty obvious that it's not going anywhere...


But of course, motion is relative. The best example would be a boat- are effects stationary relative to the boat, or to the ocean, or to the underlying world, or what? Boats at least are slow- airships, trains, cars, and spacecraft can be much faster.

Do I just need to come up with it based on what makes the most sense? Keep in mind that while it's silly not to be able to make a permanent image of a closed door in a hallway in your pirate ship, it's far more devastating to have a ballista that shoots prismatic spheres. I'm hoping for an interpretation that allows the first and disallows the second, and I can just tell my players that.

[Toliudar]

You could tell your players that you, as the DM, establish the frame of reference for any given spell. If they try to do something that mucks about with the laws of the universe in a way you don't think serves the game, assign it a frame of reference that prevents this.

[NichG]

I had a campaign in space where this was critically important. Basically all large objects pushed their reference frame outwards with a sort of field akin to gravity, except encoding the reference frame of the source. So if you cast a wall of force on a spaceship, it'd stay stationary relative to the ship. But if you crashed that ship into a planet there'd be some point at which the planet's reference frame would gradually start to overwhelm the ship's, and the Wall of Force would come to a halt rather than coring the planet.

There were also things like solar winds that caused the reference frame fields to be very unstable in space, so no one wanted to use Wall of Force shields due to the 20% risk that they'd blow backwards through the hull.

'Nearest big cohesive object' is probably a reasonable way to do it, and when that object changes, so does the spell reference frame (gradually, of course). That way you can illusion your pirate ship but not fire prismatic spheres from a cannon (well you can, but its harder and they'll stop before they core the target).

[cfalcon]

The players know that my rulings will stand, of course. I'm just hoping that there's a way to do this that can be counted on in general.

[cfalcon]

'Nearest big cohesive object' is probably a reasonable way to do it, and when that object changes, so does the spell reference frame (gradually, of course). That way you can illusion your pirate ship but not fire prismatic spheres from a cannon (well you can, but its harder and they'll stop before they core the target).

This is good, thank you much!