Determining radius with squares

[Kershek]

Consider a 10-foot radius burst. Is this what you think it looks like?


.XX.
XXXX
.XX.


If so, you're not targetting a square. Instead, you're targetting one of the corners of a square. But it's obviously 10 feet on each side. How do you deal with this? Do you allow targetting a specific corner of a square like this? It could be very significant based on which corner of the square you place the spell and the placement of the enemies.

You might be wondering why I'm asking. Look at the spell Ice Knife from Tome & Blood. After a ranged attack to hit, it showers ice crystals in a 10-foot radius burst centered on where the shard lands. You can't center it on a square, so you have to center it on a corner. Are you able to choose which corner on which you want it centered? What if you missed the target and it hits based on the grenade scatter rules?

 

[Sir Hawkeye]

the easy way is to just allow
. . X . .
. XXX .
XXXXX
. XXX .
. . X . .
which only hits one more square than the corner-centered one.

That aside, I would suggest using the scatter diagrams (the 1d4 one for hits, and others for misses).

Edited to improve diagram.

 

[Kershek]

Actually, yours hits 13 squares instead of 8, which is a lot more than one square difference.

 

[Sir Hawkeye]

You missed a row. Your original should hit 12.

. XX .
XXXX
XXXX
. XX .


Of course, I should have noticed that the first time through.

 

[Kershek]

Ah, yes, I see that now. Thanks.

 

[kiznit]

As a DM -

I usually ask a player to pick a square then I roll 1d4 to pick a corner. It adds a slight element of randomness to the area effect of a spell. This is after I got tired of players spending up to two minutes carefully calculating the exact edge of their circle effects with a tape measure to ensure maximum coverage and minimum friendly fire.

Think about it. Can you look at a point on the ground up to fifty feet away and trace an exact 10-ft diameter circle around it? I doubt it.

I also think it kinda of reflects the slight urgency and excitement that casting spells in combat would do. If the players have the element of surprise and the time to prepare, I let them pick a specific corner.

2 coppers

 

[Kershek]

Think about it. Can you look at a point on the ground up to fifty feet away and trace an exact 10-ft diameter circle around it? I doubt it.

I don't have a 21 intelligence (oh, wait, up to 26 with Fox's Cunning) and cast spells for a living. Once again, real life doesn't pertain here.

 

[kreynolds]

Instead, you're targetting one of the corners of a square. But it's obviously 10 feet on each side. How do you deal with this?

Actually, when you place a fireball, you pick a corner of the square. Now, draw the circle. Any square that is at least half covered by the circle is effected. dcollins has site with some info on this, and it's really useful. You can check it out here.

 

[Ranger REG]

For fireball, assemble and use the spell area template provided in Dragon magazine #301.

 

[dcollins]

Re: Re: Determining radius with squares

Thank you for the mention, KR.