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[PatrikLundell]

I have the problem that invaders frequently enter the map, and then slowly drift back and forth along the map edge without finding any of the entrances to the fortress, despite literally climbing down into one of them, only to exit again. If I'm really lucky they find some animal to chase so they find an entrance they like. If I'm moderately lucky they leave after a season, but usually they drift in the outermost tile row of a standard 3*3 embark for a year before leaving.

I've also had cases where the invaders are indifferent to an entrance, but once they find one they like, the previously ignored one becomes attractive if the approved one is closed off.

Does anyone understand what causes some entrances to be "approved" and other to be ignored, and better still, can describe how to make attractive ones, preferably ones that can draw the morons all the way from the edge of the map into an entrance?

Sending the militia out is not an option. Engaging undead armies outnumbering the under equipped and poorly trained militia 5-10:1 is suicidal.

[PyroTechno]

Sounds like a pathing bug. If you can make it repeatable, you should report it, and possibly upload the save to DFFD and link to it in your report.

[PatrikLundell]

It happens to almost all my fortresses (and I believe I have reported it almost a year ago), and sometimes some siegers work as they should, while others drift aimlessly, even though they seem to enter the map very close to where the other one entered. Undead seem to be slightly more clueless than goblins.

I'm currently embarking only in perfectly flat embarks according to the theory that they can't handle elevation differences well, but that doesn't help.
It seems moving my entrance tunnels underground rather than building corridors above ground has made things slightly worse.

[gchristopher]

There's some bug reports out there, but I don't remember seeing much conclusive.

I recall some discussion of Toady announcing that he'd improved game performance with pathing changes. Especially on larger maps, invaders have a hard time finding the fortress at all.

I suspect that one trick used is to precalculate parts of the map. Cavern undead have a weird behavior where if you breach the cavern, they reliably (within a set radius) come running to the tile where the breach, then they mill around randomly in your tunnel, but will not path back into the cavern. One result is that you can have dozens or hundreds of undead piled on top of each other in the first 10 tiles of a tunnel that breaches the caverns, but they won't figure out to walk up the stairs and attack the fortress.

I've tried a variety of ways to get them moving, but never came up with anything conclusive. Mostly I think pathing just doesn't work as well in the current version as it did in some previous versions.

[PatrikLundell]

I'm looking for ways to work around the pathing issues so the invaders will find the fortress until the pathing issues are addressed and design can be done more freely. Any "do this" and "don't do that" with respect to making the invaders find the fortress would be useful.
I've heard the surface uses some kind of precalculation that causes major modifications to it to screw up pathing.

If your cavern breach example applies to the surface as well, then my current approach to channel down and build a recessed courtyard that's then paved over (with underground tunnels leading to it) is catastrophic, since the breach location is floored over, so invaders would look at that point and find nothing.
However, I've had a lot of problems with my previous approach as well, where I've build a courtyard, roofed it over, and then build an access "tunnel" for the caravans as well, but possibly less invader pathing problems with that approach.

[TruePikachu]

I believe that invaders attempt to path to your meeting areas, which are defined as follows:

• No areas designated: The area where the embark wagon is/was
• Areas designated, embark wagon not deconstructed: Both the wagon and the designated areas
• Areas designated, embark wagon deconstructed: Just the designated areas

As a result, there is always at least one area for invaders (who wish) to path to. Of course, if the invaders and the destination are considered unpathable (there is no path between the two), the invaders will discount the destination, which can result in there being no destinations for invaders to head for.

I'm not familiar with the invasion technique used by the undead, but in general, if a unit is such that it wants to path "into" the fortress, it looks for these meeting areas and, provided there is a path, uses it.

[PatrikLundell]

I've previously thought the meeting area was the target, and I think it probably is, but I also suspect there is more to the pathing than the existence of a path, since the path exists in all my problematic invasion cases, so something else causes them not to find it/use it. Fort invading cavern critters usually have no problems finding the path (although I don't know if they sometimes stop a bit in, since I normally deal with them at my entrances to the caverns).

I've tried the theory that invaders fail to find the path if it involves passing above the meeting area before going down and then back towards the starting point a few tiles, but eliminating such paths doesn't help.

I've never had a problem with caravans being unable to find a path when one exists (although they sometimes take unexpected routes, especially when leaving), and my trade depot paths are generally most of the way to the meeting area.

If the invaders would path to where the embark wagon was on failure to use the meeting area path I could see some kind of logic behind it, but just randomly drift along the edge, not even reaching any part of the center tile at any time for a whole year is rather annoying. Closing off the fortress entrances won't get the morons to move to the embark wagon location either.

Undead in particular, but also goblins, can sometimes "pick up the scent" when drifting sufficiently close to an "approved" entrance, at which time the make a beeline for it. Undead, in particular, seem not to communicate with each other, so only the ones picking up the scent will move, whereas goblins at least bring their sub group with them.

[PatrikLundell]

Another failure. The morons (undead, lead by an apparently brain dead living goblin) are drifting and have come within 30 tiles from my original down staircase. For whatever reason they can't perceive the straight path there. A bunch of morons drifted somewhat south and came close enough to my south path to the same entrance to sniff it and run for it, but the main group keeps drifting aimlessly. They might be thrown off by the fact that the path is a built one on top of my recessed and covered courtyard.

Layout:

WWWWWWWWWWWWWWWWWWWbWWWWWWWWWWW
W                 WcW         W
W                 WcW         W
W                 WcW         W
W                 WcW         W
W                 WcW         W
W                 WcW         W
W                 WcW         W
W                 WdW         W
W                 WbW         W
WWWWWWWWWWWWWWWWWWWbWWWWWWWWWWW
    bbccccccccccdbbhbbdcccccccbb
WWWWWWWWWWWWWWWWWWWbWWWWWWWWWWW
W                 WbW         W
W                 WdW         W
W                 WcW         W
W                 WcW         W
W                 WcW         W
W                 WcW         W
W                 WcW         W
W                 WcW         W
W                 WcW         W
W                 W W         W
W                 W W         W
W                 W W         W
W                 W W         W
W                 W W         W
WWWWWWWWWWWWWWWWWWWbWWWWWWWWWWW

W = Wall
b = raising drawbridge, two tiles long (image missing one tile jutting out on the top and bottom)
c = cage trap
d = door
h = hatch
 = clear ground

The morons are to the west, with the map edge 53 tiles from the hatch. The doors are unlocked, as is the hatch. The drawbridges are down, except for two periods when I collected first the splinter invaders from the southern cage traps, and then a copperhead snake woman chased into the west arm.
The reason for the boxes in between the arms are for future orchards and to block camping invaders from camping on the sides of the arms when a "leader" has been caught in a trap (I have had that problem in the past).
The courtyard is below the right half of the western branch.
The hatch leads down two levels to a 10 tile southward tunnel (with an unlocked door and cage traps inside an open airlock) into my workshop. When the invasion started my meeting area was some 10 tiles south of the workshop entrance (a season later I moved it downwards, with no change in invader behavior).

The embark wagon stood a few tiles to the NE of the NE corner of the whole structure.

The embark is completely flat with the ocean to the north and east to restrict the room for morons to drift, so land comprises about 1/3 of the 3*3 embark.

[TruePikachu]

Okay, so many of the zombies follow a single "leader".
Are they getting distracted by anything? I'm not sure it applies, but building destroyers will prefer to destroy buildings.
If the path is one such that dwarves can path to it (along the ground), there shouldn't be any problems. What happens if you construct some piece of furniture (so it's in an easily-dwarf-accessable stockpile), and try to build it near the zombies; is the furniture found? If the piece of furniture is indeed found by that list to choose what specific piece to place, I'm stumped. If it isn't found, there isn't actually a path...

[Goatmaan]

Maybe the morons remember that a long 1 tile wide hallway is how they became zombies?
Try widening it to 3. Sprinkle the traps out a bit, and add a few slicey dicey pokey smashy ones in too!!
Gotto make them "think" they have a chance.
Cuz their standing around going "I'm not going first into that redeath trap!! You go first, I'm right behind you!!" "No, no!! YOU go first, I insist!! Besides I already died today.. "

   Goatmaan

[PatrikLundell]

Nothing to distract them except the echoes in their heads (the Copperhead Snake people had to wander into them to get killed). OK, they did fire bolts at birds at some point.
I've never seen a dark tower siege force containing building destroyers, and this one is no exception. Goblins, elves, and humans only, I think. Even if there were any, my juicy doors should do the trick. My dorfs have had no problem using any of the 4 corridors to gather the logs from the embark, so there is nothing wrong technically with any of the paths (And the Copperhead Snake Man who got away from the undead got caught in the outermost trap in the branch the undead are unable to find, and my dorfs collected the captive without problems (I'd closed the drawbridge outside for protection during the cage retrieval).
The sieger problem is not an absence of functioning paths, but failure on siegers to find any of those existing until they get close to one by accident (and "close" sometimes probably means halfway down one, in the cases where they back out).

@Goatmaan: This problem has plagued me in most of my fortresses for over a year (IRL), and I'm not in a mood for "funny" suggestions. I'm somewhat surprised it isn't a widespread issue, so somehow I do something DF doesn't like, but I try again and again to find some approach that doesn't suffer from it, without success.

Edit:
After more than half a year the invaders drifted close enough to the southern entrance to smell it and a few more were caught, I collected those, and a new batch were caught. I then closed off the southern entrance to allow my dorfs to collect the new gift bringers, and suddenly the invasion handler fled. That strangely enough prompted the remaining invaders to rush the previously uninteresting western entrance, as well as the eastern one, so I think I caught everyone except the handler, who seemed to be the one to BLOCK the invaders from finding the fortress. Weird, although the remainders might have smelled my dorfs working behind the closed drawbridge?

[Goatmaan]

Patrik,
 Yes my suggestion was "meant" to be funny!
But if you reread it I offered a viable solution.
In you're reply to me, you said "most forts" did you have that same setup in them?
"Surprised the problem isn't widespread" " must be someting I'm doing in my forts"
 That sounds like you need to change "something" about you're setup, hence my suggetion.
You're design may be "technically" correct, but this IS Dwarf Fortress we're talking about, right?
And to be technical many things are "not working as intended"

So get out of you're safe zone, and have some fun.


Edit: Upon rereading that last bit came out a little to strong.
 I meant you should try like Monty Python used to say 'And now for something completely different! !"

  Goatmaan

[PatrikLundell]

The problem is that I AM trying a lot of different approaches, with the common theme being cage traps, drawbridges, and corridors (and the fortress itself below ground, although the courtyard has been both above ground and recessed). I have a trade depot entrance I didn't mention, as it ends up at the other end of the embark and starts in my courtyard. On most of my embarks the trade depot entrance (3 tile wide) has had greater problems attracting invaders than the main one(s).
Each embark I change at least something in the hope of it getting the invaders to find the fortress, but I'm running out of theories on why they fail to find the (very existing) paths.

I understand the comment was meant to be funny, and I tried to convey the message that I am not a willing receiver currently. It's hard to get anything done when you have to watch siegers closely a year at a time in case they might suddenly find the fortress and rush it (especially with the rather weak defenses of the current fortress). Giving up and just turtling until they leave would work, of course, but that's, well, giving up.

- Maybe they can't handle paths with varying elevation? Perfectly flat embarks.
- Maybe the distance to the fortress is too large for them to find it? Ocean embark with limited distances due to the limited amount of ground.
- Maybe they can't find a path that doubles back above/below the meeting area? Make sure none of the paths require such a route.
- Maybe they can't find a path when it digs down into the ground far away? Make the paths short and above ground.
- What about one path in each direction rather than a main entrance and a trade one? Ain't working too well...
- etc.

I'm considering to move back to my early design (above ground courtyard with a trade entrance that's later on converted into a main one, with a separate longer trade entrance) since those fortresses were found at least occasionally (virtually all of them had drifting siegers as well).

And, by the way, another undead siege force has arrived. This time they've spent the first season in a 20*20 area in the lower left corner of the embark (still only about 50 tiles from my hatch). If I get some time between sieges I'm going to build retracting bridges along the edge to drop them into cages.

[Goatmaan]

I'm still on .19, my current quest has kept me busy for a long time. So I've never messed with undead.
That said, have you tried bait? Do undead even attack animals? Pasture whatever critters you (they)  like about 10 tiles apart...leading to entrance.
 Tried bunkers 20+ tiles out? (Archery/ballista) not to kill, but to lure them to entrance.
Tried walls to try and funnel them?
Tried using a sacrificial lamb,er dwarf, to run out and smack them?

 Ok I'm out of ideas,

   Goatmaan

[PatrikLundell]

Undead attack everything, so bait works. However, you'd have to tie them up 10 or so tiles apart, and even so, only the few undead that happen to scent the animal will attack the next one, so it's quite bait intensive, and you don't really know where they'll show up, so you'd basically have to sprinkle the map with bait beforehand. Trying that with free ranging dorfs will probably have the scenters kill the fleeing dorf and then walk back to their handler.
I think I've actually tried chained bait early on.

Haven't tried bunkers, but since undead bring ranged weapons with them, the marksdwarves (whom I'm not using) would be in significant danger, and given how uncontrollable military dorfs close to a fight is, you'd probably not be able to pull them back. I've considered ballistae, but I doubt the undead would react to being fired at. If it had been possible to put ballistae on rails to make it possible to aim them I'd have made use of them (I actually built a few in one fortress, but the enemies never came within their firing directions after that). I've also considered 20 tiles high (i.e. out of sight/disturbance) platforms to drop stuff on top of drifters (tower up from the fortress and then out to the edge). That's a lot easier by the ocean where there isn't as much edge the enemies can hug. If I'd finished the orchards I would certainly consider using them for ballistae (which is what I did in my previous attempt), but currently these areas are accessible only from the outside (and it's quite possible the undead would find the path to the north up the stairs and then down to their prey if they scented dorfs).

I've tried walls early on, and it just made them less likely to find the fortress since they'll drift back and forth along he wall, not through the passage(s) in the wall. It basically restricts the handler's brownian motion options.

I've occasionally tried using civilian dorfs as bait for enemies camping by my cage traps, but they are in grave danger from missiles, and frequently they just run away before the campers react to rush the civilians (and into the traps just in front of them).

Anyway, the second group of siegers left after only a season, and I don't think they ever came further than 15 tiles from the SW map corner...
Two 10*10 holes with one tile in between have been channeled out and are in the process of being covered by retracting bridges. I'll gradually add more.

I appreciate your attempt to help.