D&D 5E SPIRIT GUARDIANS range clarification

[Voadam]

Use plain language then.

Sure.

If I draw a 10' radius around an (object or person), do I measure from inside the object or person, or outside of the object or person?

If you are drawing a 10' radius circle around an object or person the 10' radius circle should be centered on the object or person. You should measure from the center point of the person or object. Very straightforward

Natural language suggests the 10' radius is drawn from the outside of the object or person, seeing as it avoids the absurdity of a 10 radius around something that is bigger than 20' across, not have a 10' radius around them, but instead have the 10' circle be wholly inside of them.

For D&D the typical case is a medium or small size person who will comfortably fit completely within a five foot radius circle. There is no problem with the typical case. It only becomes an issue with corner case NPC types of things like the gargantuan dragon casters.

Like assume I (right here and now) instruct you to go away and draw for me a '10' radius around your house'.

Using plain natural language, do you then draw a 10' radius circle inside your house, or around the outside of it?

If I was given written instructions to do so and could not clarify your actual intent I would infer that you mistakenly said 10' radius and meant a line 10 feet away from the house on all sides. Which wouldn't be a circle or a 10' radius.

If the instruction however was to "draw a 10' radius around a box" I would assume you probably meant draw a 10' radius circle centered on the box and not a line that was mostly oval to conform to the shape of the box and a little bigger than a 10' radius circle, though both are possible intents from the imprecise phrasing.

 

[Voadam]

If you play without a grid, then the whole thing is not an issue in the first place. I'd simply measure the distance from the caster center to the target center and if it's 15ft or less, it hits. I wouldn't have to care about area of control at all here.

Even easier, I'd just allow my players and also the monsters to just be like "I stay at 16 feet distance and shoot an arrow at it". No need to overcomplicate things when working without grid.

Only applying the optional grid rules creates this problem in the first place.

No, its an issue both ways.

With no grid it is still either 15 feet from the center of the gargantuan dragon cleric or 15 feet extending from both ends of the 50 foot long dragon.

In your example if you are 15' 3" from the center of the cleric you are within 15' of the edge of the cleric. Not really a big issue that will come up for normal size people casters the way it would when measured in five foot square increments, but the difference on ridiculously giant casters could be narratively significant.

 

[DND_Reborn]

So, here is a house (10' grids) with a zone of 10' distance around it.

Anyone within 10' of the house will trigger the alarm (light, whatever) system.

No need to use the words radius or around. Being "within" X feet (without a directional component) automatically implies "around" and the radii on the corners also get created by default.

 

[Voadam]

Radius is also used outside of strict mathematics to indicate an area around a site that isn’t necessarily a single point in geometric space. You’ll find plenty of places advertising that they deliver goods in an x mile radius of their store or the mall they’re in.

I would not expect the difference of the size of the store to be a factor when determining whether something is within a five mile radius of the store. When looking at the map I would expect the delivery area to be a five mile radius circle centered on the store as the base assumption, not a base assumption of a five mile radius plus an exact distance of a hundred feet or so depending on the store or mall, but also I would expect the exact edges to be a little loose in such things.

Mesuring out from the edge of the store would also not be unreasonable for roughly determining whether you are within the delivery area, as I don't think the difference would generally be significant on the scale of miles.

 

[Hriston]

What if it is that big? Are you saying the Globe appears inside the creature?

Not necessarily, the creature could appear to shrink to fit inside the globe. What I'm imagining is that when the gargantuan cube casts globe of invulnerability, the image of the cube is replaced by a shimmering 10' radius globe with a smaller image of the cube inside of it. I think that's one way of reconciling the spell's description that the barrier is "around" the caster with the fact that it specifies a 10' radius sphere as its AoE.

No, the spells I referred to expressly state they create the 10 or 15' radius around you (the caster).

If I draw a 1' radius around a circular power or telegraph pole (that itself has a radius of 2'), is the circle I drew inside the pole, or 1' outside of it?

If the circle you drew has a 1' radius and is centered on the pole, then it would be inside the 2' radius pole. Putting the word around in your description of what you've done is a nonsense.

 

[Flamestrike]

So, you want to use the "bone definition"? How will that help your argument...

(Which I don't understand why you are even arguing...)

No. I can say 'there are no burglars within a 50m radius of this city block' which is one of the examples used.

It means there are no burglars within 50m of the city block, and the block is square.

You can use radius, not in strict geometry terms, but something 'radiating' from something.

 

[Flamestrike]

If the circle you drew has a 1' radius and is centered on the pole, then it would be inside the 2' radius pole. Putting the word around in your description of what you've done is a nonsense.

Whats nonsense is your interpretation that something that is 'an X radius around a person (the caster)', can literally be inside the person if the caster is bigger than X. Or now you're trying to argue the magic also shrinks the caster to fit inside it as well as the spell effect.

Your interpretation leads to an absurd result, and thus is to be ignored, in favor of one that doesnt.

 

[Flamestrike]

If you are drawing a 10' radius circle around an object or person the 10' radius circle should be centered on the object or person.

So when I say 'You are not allowed to enter within a 10' radius around that Football stadium', you interpret that to mean 'I cant enter a 10' circle inside the stadium and in the middle of it?'

I hope you never get a restraining order placed on you, because the above would be a breach of the order.

 

[Flamestrike]

It is my position that the trap is described poorly and misusing the word radius.

Raidus means other things than a circle. In this case it means 'radiating out from the creature that cast the spell X feet, and filling that volume.'

 

[NotAYakk]

Wow... you REALLY just don't get it, do you? Why are you still debating this with me?

Radius is a geometry term. Period. If they don't mean that, (WHICH I AGREE WITH YOU THAT THEY DON'T, OK?????? Got that?), they should use a different term and then we wouldn't be discussing it. Would we?

"Zone", for example, would be a better term. A "zone" is an area, and can be "around" something or someone.

You are using radius wrong.

More specifically, you are taking one geometrical use of radius that you happen to be aware of, and declaring that any other use is wrong.

That isn't evidence you are right. That is evidence you only know of some uses of the word radius.

Any wedge of a circle can be said to have a radius, not just circles. So can any curve -- this is known as the radius of curvature.

If you want a formal geometrical definition, radius around a non-point object can be mathematically described by creating a derived metric where the distance between any two points in the object is defined to be zero, and that "short cut" can be used to measure distances between other points. Then do the usual equivalence classes of neighborhoods.

This reduces the object to a single point in a metric space, and we can now define a sphere of radius 15' around that single point. All points in this modified metric space correspond to points in the space we derived it from, so we can map this back to the original space.

If the original object was (say) a 5' cube, the 15' radius sphere centered on that 5' cube is a 20' radius cube with rounded corners. Those rounded corners have a radius of curvature 15'.

Is that mathematical enough?

I suspect not; I suspect you aren't actually interested in radius as a mathematical concept other than insofar as it supports your position. But, if you are only using radius as a mathematical concept insofar as it supports your position, then radius as a mathematical concept doesn't support your position.