Detect magic vs invis

[HandofMystra]

Last night one of the players in the group cast detect magic in the direction of an enemy spellcaster. The DM ruled that detect magic at first level cannot replicate See Invisibility at second level. I would argue that detect magic needs three rounds to get the location of an invisble creature while See Invisibility only needs a standard action. Not to mention that detect magic requires a spellcraft check to tell disambiguate the invisbille thing from other magical places in the detect zone. How do you play it?
This brings up an interesting question: if an object is in the detect magic cone during round one of the spell and moves to another location within the detect zone in round two, how many rounds does the caster need to identify its position?

 

[Lonely Tylenol]

Detect magic works this way:

round 1: there is a magic aura in my 60 ft. cone
round 2: the magic aura is in this particular direction
round 3: the magic aura is in that square

Add in the Spellcraft check and you get: the magic aura is an Illusion school effect.

That's the best you can do. You can take a guess that the illusion aura is an invisible creature, but all you get is the 5 ft. square it's located in (assuming it fits in a 5 ft. square). You certainly can't see the creature, and can't target it with spells, but you can attempt things like attack rolls to hit it, with all the penalties associated with attacking invisible creatures. If you stop concentrating, or it leaves your 60' cone, you must begin from round 1 again.

 

[Archade]

Dr. Awkward has it right ... that's how our group handles it.

 

[szilard]

Detect magic works this way:

round 1: there is a magic aura in my 60 ft. cone
round 2: the magic aura is in this particular direction
round 3: the magic aura is in that square

What happens if the invisible thing moves to a different square between 1 and 2? between 2 and 3? after 3?

-Stuart

 

[Ranes]

Actually, it's:

Round 1: Presence or absence of magical auras in the 60' cone
Round 2: Number of auras and power of the most potent
Round 3: Strength and location of each aura. For aura(s) in line of sight, make spellcraft checks to determine school. Magic areas, multiple types or strong local emanations may distort or conceal weaker auras.

What happens if the invisible creature moves depends, at least partially, on where it moves. If it moves out of the cone, clearly, the detecting creature must re-direct the cone and start again at step one. If the invisible creature moves to another point within the cone, then:

Round 1: no change
Round 2: potential for change based on the previous round (1) if there was no aura but there now is one
Round 3: potential for change based on the previous round (2) and current one, based on change in number of auras and possibly the strength of the most powerful in round 2 being different to the strength of the most powerful in round 3

So if an invisible creature stays within (or enters) the cone in or before round 2 and moves but stays within (or if it enters) the effect in round 3, you detect that there's an illusion in round 3 and, depending on the number of auras you detected in round 2 and the number you detect in round 3, and on the possible change in strength of the most powerful aura you detect from round 2 to 3, you might be able to deduce that there's an invisible creature in the cone. If you do, you'll know what square it's in, that round. Any subsequent rounds that it moves within the cone you're concentrating on will make it fairly obvious that there's a mobile invisible entity there and you'll know what square it's moved into.

Basically, from the third round of concentration onwards, I'd rule that magic auras that move within the cone are automatically located - but with the caveat already mentioned that multiple auras can distort or conceal weaker auras.

 

[Archade]

Y'know, this just makes Nystul's Magic Aura so much more useful ...

 

[kayn99]

Under detect magic it says you must have line of sight to get a spellcraft check to determine what school it is; Under line of sight it say, if you can not see the target you can not have line of sight. So I guess you can locate the square, but you will not be able to figure out what school it is. At this point you may be able to make a logical guess.


Kayn

 

[Ranes]

Exactly. You're locating an unidentifiable aura which may or may not 'appear' to move. Thanks for spelling that out, Kayn. I used the phrase 'might be able to deduce' without going on to qualify that.

 

[Quidam]

LoS to the Aura

Under detect magic it says you must have line of sight to get a spellcraft check to determine what school it is; Under line of sight it say, if you can not see the target you can not have line of sight. So I guess you can locate the square, but you will not be able to figure out what school it is. At this point you may be able to make a logical guess.

I would interpret that to mean you must have line of sight to the aura that is being examined, not line of sight to whatever is giving off that aura. It's the aura that's being examined, after all, and it is visible.

 

[Hypersmurf]

I would interpret that to mean you must have line of sight to the aura that is being examined, not line of sight to whatever is giving off that aura. It's the aura that's being examined, after all, and it is visible.

Is it?

Arcane Sight says you see auras. Detect Magic says you detect them. You know they're there, but you can't see them.

And Detect Magic is quite clear about what you need line of sight to:
If the items or creatures bearing the auras are in line of sight, you can make Spellcraft skill checks to determine the school of magic involved in each.

Arcane Sight has the same wording... so if there's an invisible creature standing in the open, you can see the aura of the invisibility spell, but since you don't have line of sight to the creature bearing the aura, you can't determine the school with a Spellcraft check.

One advantage of Detect Magic over Arcane Sight, of course, is that Detect Magic can work through certain thicknesses of solid objects, while Arcane Sight only lets you know the location and power of magical auras 'within your sight'... so something in a box or behind a door is concealed from Arcane Sight, but not from Detect Magic.

-Hyp.