Determining line of sight vs cover

Nikosandros · Oct 15, 2008

I am trying to figure out if I'm reading the rules correctly.

On page 273 of the PHB we read that when determining LOS, a line can't touch an obstacle. Next page, we see in the drawing that LOS is obstructed by touching the corner of a wall. On the other hand when determining cover: A line isn’t blocked if it runs along the edge of an obstacle’s or an enemy’s square. (p. 280). This in confirmed in page 43 of the DMG: A line that runs parallel right along a wall isn’t blocked.

When a line runs parallel to a wall it in fact, touches the obstacle. So, are the rules for LOS and cover different?

Are those two examples correct?

1) A character is shooting around the corner at someone in a corridor. The target doesn't have any cover, because we have line that runs along the wall.

2) A character is shooting around the corner at someone behind another corner (a U-shaped corridor)

1+++++++++++++2
..........................

for the purpose of cover there are two unobstructed lines from square 1 to square 2, however there is no line of sight.

JGulick · Oct 15, 2008

Nikosandros said:
I am trying to figure out if I'm reading the rules correctly.

I think the difference here is that Cover is determined from EVERY corner (1 or 2 blocked = cover, 3 or 4 blocked = superior cover) whereas LoS is determined from only the Best corner (even just 1 unblocked = have LoS). So, in your example, you could have LoS determined along corners not touching the wall (say, from the bottom front corner of 1 to the top front corner of 2). LoS and (because of the "following the wall" exception in the Cover rules) no Cover.

Kordeth · Oct 15, 2008

JGulick said:
I think the difference here is that Cover is determined from EVERY corner (1 or 2 blocked = cover, 3 or 4 blocked = superior cover) whereas LoS is determined from only the Best corner (even just 1 unblocked = have LoS). So, in your example, you could have LoS determined along corners not touching the wall (say, from the bottom front corner of 1 to the top front corner of 2). LoS and (because of the "following the wall" exception in the Cover rules) no Cover.

Not quite. Cover is determined by one corner of your square and every corner of the target square, LOS is determined by one corner of your square to any point in the target square, not just a corner.

Hypersmurf · Oct 15, 2008

Nikosandros said:
2) A character is shooting around the corner at someone behind another corner (a U-shaped corridor)

1+++++++++++++2
..........................

for the purpose of cover there are two unobstructed lines from square 1 to square 2, however there is no line of sight.

There is also no line of effect (PHB p273: "If every imaginary line you trace to a target passes through or touches a solid obstacle, you don't have line of effect"), so someone in square 1 cannot make a ranged attack on square 2 ("You need line of effect to any target you attack").

-Hyp.

Ravingdork · Oct 15, 2008

Thought this might help clear a few things up.

CubeKnight · Oct 15, 2008

raven_dark64 said:
Thought this might help clear a few things up.

That was extremely helpful. Huge thanks!

Syrsuro · Oct 16, 2008

Note: The cover rules in the PHB are the 'simplified' version of the rules.

The DMG (page 43) gives an optional approach which restricts the PHB version of cover to ranged, close and area attacks, but gives a different approach to be used for melee attacks.

Thus, for example, under the DMG system a creature that is right around the corner from the combatant (see the bottom left of the earlier posted diagram - "PC#3 has no cover from M#3") has no cover from a ranged attack by M#3, but does have cover from a melee attack by M#3.

Carl

Nikosandros · Oct 16, 2008

What about a defender behind an arrow slit?

He has superior cover in melee, but it would seem that he can't be targeted by a ranged attack. LOE can pass through the slit, but cover must be determined using the corners of the target's square.

cjais · Oct 16, 2008

It would seem that area bursts can easily ignore cover.

In the case of area bursts, cover is determined from the origin square. So firing a scorching burst through an arrow slit would provide no cover to the enemy hiding behind it, as it would instantly place the origin square on the enemy, and as there's no cover between the origin square and the creature (they occupy the same square), he would have no cover, even if the wizard had to aim the burst through a pixie-sized keyhole.

Is this a correct interpretation of the rules?