Cone from above

[Vrecknidj]

I have a party that's about to get attacked by a dragon. The dragon has Adroit Flyby Attack and happens to have a 75' cone breath weapon. The dragon will probably be concealed when it makes its attack (it's a shadow dragon on the plane of shadow).

I'm planning for the dragon to send a bunch of ground forces into the fray to keep the party busy, and then it'll fly over head, launching its breath weapon onto the group as it flies by.

From the perspective of a ground-based dragon, the cone would be 75' long and 75' wide at its terminus. From the perspective of flying overhead, the dragon could affect a 75' diameter circle if its breath weapon were maximally affective.

Anyone see anything wrong with my just assigning a 75' diameter circle as the area of effect when I pull this off?

Dave

 

[DanMcS]

Nope. Dragons are wicked smart, and would be able to figure out something like this. Make sure to allow your players to use the same kind of 3D thinking, ie, "the giant is 20 feet tall, I should be able to hit him with my lightning bolt without hitting the PCs fighting him".

Only complication I can think of is that if the ceiling isn't 75' high, make sure to reduce your cone-floor-intersection diameter accordingly. This might be desireable for the dragon, even, since he can have forces on both sides of the PCs and still hit only the PCs.

 

[Plane Sailing]

In 3.5e they changed the definition of cone spells from the sensible and usable "diameter is the same as the range at any point of the cone" to the incomprehensible "Cone is a quarter circle heading away from you".

So a 75ft cone at 75ft range could (by an ultra-strict interpretation) only affect a few 5ft squares because of the rounded end of the cone, or by a mathematically strict definition it would be a circle of a radius defined by the chord across the quarter-sphere... and I can't remember the maths to work that out off the top of my head.

Remind me again why they changed spell effect descriptions in 3e? Something about simplifying things?

 

[Vrecknidj]

Okay, let me get this straight. A "cone" isn't a cone, it's a quarter-circle. Um, ok. So a cone from above is, what, a quarter-circle sheet that's one "square" thick? Why would dragons have a breath weapon of that silly shape?

Scrap it.

I'm going with a cone being conical. I'll work out the math and leave it at that.

Thanks for the replies--it's given me more reasons to use house rules.



Dave

 

[Someone]

A cone from a spell is a quarter circle. A dragon´s breath cone, by the SRD, continues to be "as high and wide as its lenght".

You only need to house rule if it´s a wizard casting cone of cold from above

And better not to think if any of them launch the cone and the inclination isn´t 0 or 90º

 

[Staffan]

it would be a circle of a radius defined by the chord across the quarter-sphere... and I can't remember the maths to work that out off the top of my head.

Since the cone is a quarter-circle, it's not that difficult. Basically, a 3.5e cone is twice as wide as a 3.0 cone: 90 degree "point" instead of 45 degrees. So the cone radius would be equal to the distance.

Now, if you're starting to aim the cone in other directions than "straight forward" and "straight up/down", that's when the trouble starts...

 

[Someone]

Not exactly. Once you do the math (I can post them if you require it) the cone´s radius equals 1/(square root of 2) of the quarter circle´s radius, aproximately 0,71. Therefore, a cone (quarter circle actually) of 60 feet shoot directly downward means a circle with a maximum radius of 42,6 feet: a diameter of 85 feet. The wizard hast to fly at 42,6 feet, too, to get a circle this huge.

 

[HeavyG]

Someone, your math is right, but if you take the whole diameter as the spell's area of effect, then some people on the edge would get full damage even though only their feet are within the cone.

What is the rule for squares with partial overlapping of spell areas, again ? Can't remember...

If we want to keep only the squares that are, vertically, completely within the area, then we have to cut a 5' deep (I do believe that combat grid "squares" are 5' high in 3D combat) section of the cone. In that case, on the 2D grid, the spell has a 37,6 radius circle area of effect, which I would round down to an even 35 feet radius for the standard 60' spell cone.

 

[Staffan]

Not exactly. Once you do the math (I can post them if you require it) the cone´s radius equals 1/(square root of 2) of the quarter circle´s radius, aproximately 0,71. Therefore, a cone (quarter circle actually) of 60 feet shoot directly downward means a circle with a maximum radius of 42,6 feet: a diameter of 85 feet. The wizard hast to fly at 42,6 feet, too, to get a circle this huge.

Ah, my bad - I was thinking of the cone as a triangle with a side = distance and a 90-degree angle on top, forgetting that there's all that wasted area in the round bit beyond that.

 

[Someone]

Not too much of a difference; the circle will probably cover most of the board anyway...