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I'm a little confused by how the LOS system works. On a few occasions I've had my units be attacked when I thought they should be hidden from the enemy. I do not mean just in Full Cover since I understand that doesn't confirm complete protection. I'm talking about instances where my units are on the other side of a raised area that should have entirely blocked sight.

One notable occasion had an alien attack one of my units when a fountain stood between them, along with two or three steps upwards making the fountain area a very high section.

Are there any tools, options or recommendations on how to better judge my troops visibility?

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  • Disregarding retcons like described below, I have had instances where none of my squad had the little red alien icon indicating a visible enemy from their vantage point, and yet that alien managed a good shot. In one particularly memorable moment, I knew it was there because I was maneuvering, it was the last alien on the map, and in I had free actions to take with all squad members so I would have taken a shot with each of them if possible (so opted for overwatch instead). I verbalized something unrepeatable to the empty room.
    – horatio
    Commented Oct 16, 2012 at 18:24
  • I've found there are also situations where you don't get LOS when you should. For Example
    – AnnanFay
    Commented Oct 24, 2012 at 17:42
  • I agree with @Annan, I've seen LoS behave illogically a lot, while level above or level below the target.
    – vartec
    Commented Oct 25, 2012 at 15:01

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The following correct information to the best of my knowledge, but is generally based on my own gameplay experience and memory, and not backed with SCIENCE (TM). I'm happy to correct any errors noted in comments.

General Line of Sight and Cover

This Image (it's large) provides a great guide to cover and it's effects on line of sight(LOS). I found it via reddit, but I'm not sure of it's original source.

Based on my experience, low cover doesn't block line of sight, and high cover does block line of sight. However, it's important to note that if your unit is peeking around the edge of a piece of high cover, the enemy can see them peeking out, and can still establish a line of sight, even though most of your unit is behind high cover.

When thinking about cover and line of sight, it's important to consider that your soldiers are "active" at all times, looking over their shoulders, peeking out from cover, sometimes even automatically sidestepping a space to take a better shot. Being active in such a way allows your units to maintain a 360 degree line of sight, but also exposes them to enemy fire. Your unit may be in cover, but they're peeking out from it constantly to maintain line of sight on the enemy, and that gives the enemy a line of sight on your soldier.

A good rule of thumb is, if you can see your enemy, there's some kind of line of sight between him and you. If you're being shot at from within the fog of war, then I'm not sure what's going on there. I've only seen that happen when I'm hunkered down (which reduces a unit's line of sight).

Unfortunately, when all your soldiers are bunched together, it's hard to know which particular soldier is giving you visibility on any particular square. The game doesn't provide any way to determine a soldier's individual LOS when multiple soldiers have overlapping fields of view.

The Hill Scenario

For the "Hill Scenario" you described, here's what I'm imagining (side view from ground)

        __+__
  _____|FFFFF|_____
S|HHHHHHHHHHHHHHHHH|X

H: Hill (terrain)
F: Fountain (cover object)
S: Soldier
X: X-Ray

Let's assume that the fountain is a half-cover object for now. In the above section, we assume that half-cover doesn't affect line of sight. This should always be true on flat ground. However, in three dimensions, the relevant question seems to be, "if the terrain is a half-step up, and the fountain is a piece of half-cover, shouldn't that equal full cover, and block line of sight?" The image I linked to above does not address this scenario.

Realistically, line of sight should probably be blocked in this scenario. However, you got shot, so it obviously wasn't.

I'd theorize that the game simply treats low cover objects as not blocking line of sight, and doesn't actually calculate total "height" of cover.

If this is the case, we can completely disregard the fountain (pretend it's invisible and immaterial). This means that the elevation of the Hill would be the key to determining LOS.

If the side of the hill is the height of low cover, then there would still be line of sight across the hill, when ignoring the fountain.

If the hill is the height of full cover, then I feel like it should block line of sight, and this is probably a bug. I could see a possible argument that the soldier could be actively peeking his head out over the hill, creating a LOS across the hill. However, based on the unit height and animations of the soldiers, it seems like it would be very difficult for one of them to fire over a piece of high cover.

If the hill is higher than a full-cover object, then there should definitely be no line of sight across the hill, even ignoring the fountain.

If the fountain is full-height cover, then it should block LOS between the two units regardless of the hill height.

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  • Thanks for your thoughts. I appreciate that the cover system is designed to simulate your operative peeking around the cover to maintain their view. The problem I experienced concerned two units on either side of what amounted to a small hill. I would not expect the unit on one side of the hill to be able to target the unit on the opposite side ( The 'hill' in this case was steps up to a large fountain, the fountain itself and then steps down the other side.)
    – Rob
    Commented Oct 15, 2012 at 14:17
  • I have had similar problems as well inside an alien base where there was one door to get through what seemed like a solid wall and I got shot through the wall it looked like. May be that it wasn't a solid wall but it certainly seemed like it from what the camera was showing me. :(
    – Chris
    Commented Oct 15, 2012 at 14:33
  • @Rob, I've added notes on my theories for the "Hill" Scenario.
    – Jon Quarfoth
    Commented Oct 15, 2012 at 14:58
  • @Chris, sounds like a bug, but remember, bugs in determining LOS aside, if you can see the X-ray through the wall, the X-ray can see you through the wall :)
    – Jon Quarfoth
    Commented Oct 15, 2012 at 14:59
  • Oh yeah, I shot him back with overwatch fire and killed him. I still took three damage though! ;-)
    – Chris
    Commented Oct 15, 2012 at 15:01

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