UFO Flight Patterns

(Zaimoni: Some working notes. This plausibly should be moved to mainline when sufficiently detailed. While I do use MISSIONS.DAT notation to index the UFOs, this does not belong there.)

Common Observations

In spite of the game having precomputed trig functions at 1/8 ° resolution, the "turning points" are not nearly so densely packed. (I suspect a sparse latitude-longitude grid, or an explicit valid list somewhere.) It should be possible to identify the precise intermediate destination in-game, at least when it's near the equator and not at the same latitude. UFOs are notably slower at turning points.
The current waypoint appears consistent between saves. Later ones in the sequence aren't (some question about Retaliation missions)
When a UFO leaves its target region, it's leaving for good.
The next "turning point" (or landing site, as the case may be) is only generated when the current one is reached.
I have not been able to get a Retaliation mission scheduled when a UFO is shot down at the second or later "turning points". Scheduling is very unreliable even then, and is not a strict matter of either speed or accuracy.

Retaliation searching UFOs

Searching Retaliation UFOs (before BattleShip) fly slow. With XComUtil craft, it may be possible to shoot them down with a Skyranger.
Searching Retalation Battleships merely fly "normally".
needless to say, the sequence will abort if the UFO finds your base.

I am tentatively assuming that the number of turning points is fixed, but that they may not necessarily be visible to the naked eye because of practical colinearity.

Research UFOs

Research 0/0

These do not land.
Four turning points, leave.

Research 1/0

Four turning points, land, leave.

Research 2/*

Four turning points, land, two turning points, land, leave (May test 2/1 a bit more to confirm leave, but rest of sequence is directly observed)

Harvest UFOs (incomplete)

Harvest 0/0 - small scout

These do not land.
Five(?) turning points, leave.

Harvest 1/0 - medium scout

Five turning points, land, leave.

Harvest 2/0 - small scout

These do not land.

Harvest 3/0 - large scout

These do not land.

Abductor UFOs

Abductor 0/0

Six turning points, leave.

Abductor 1/0

Five turning points, land, three turning points, land, leave.

Abductor 2/0

Five turning points, land, leave.

Abductor 3/0

Six turning points, land, leave.

Abductor 4/*

Six turning points, land, leave.

Base Construction UFOs

Base Construction 0/0

5 turning points, land, 3 turning points, land, leave.

Base Construction 1/0

4(?) turning points, land, 3 turning points, land, leave.

Base Construction 2/0

6(?) turning points, land, 3 turning points, land, leave.

Base Construction 3/0

4 turning points, land, 4 turning points, land, leave.

Base Construction 3/1

4 turning points, land, 4 turning points, land, leave.

Base Construction 4/0

4 turning points, land, leave.
The alien base is placed the instant this Battleship arrives in the Earth's atmosphere.

Terror UFOs

Terror 0/0

three turning points, land, three turning points, land, leave.
Slow...until preparing to land. Pretty large difference (~450 vs ~1800).

Terror 1/0

two turning points, land, leave

Terror 2/0

These do not land (??? need more samples to document variability between instances ???)
two turning points, leave

Terror 3/0

two turning points, land.

Retaliation UFOs

Retaliation 0/0

These do not land.
five turning points, leave. (Didn't get a clear sample)

Retaliation 1/*

These do not land.
seven turning points, leave. The 1/0 I observed to count this did a very tight zigzag pattern...it would have touched any base in about 2/3rds of the nation of South Africa, and just about any base in Madagascar. This may be fluky, though. 1/1 is the same format, but the one I observed was not a tight-weave.

Retaliation 2/0

These do not land.
eight turning points, leave.

Retaliation 2/1

These do not land.
I had some problems measuring the number of turning points here. I'm inclined to think there are ten turning points, but eight is the most consistent; if I was forced to jump to conclusions, I'd say eight.
I thought I saw a six-turning point instance, but suspected that was spoiled because it had found Base Nigeria. However, the expected base attack did not happen on Retaliation 3/0, and (conjecturing that the actual base attack is coordinated in BASE.DAT) there was no odd change in BASE.DAT that would have flagged a base attack.
- AFAIK BASE.DAT doesn't contain any information pertaining to a retaliation. It stores the layout of your bases and what items are stored in them, there are some unknowns at the end however. I'm fairly certain it isn't in there... --Pi Masta 17:04, 9 July 2007 (PDT)
Another possibility is that base attack Battleships are handled in MISSION.DAT, using some oddball sub-UFO index that clearly is out-of-sequence.
Also: what does AKNOW.DAT do...it certainly is suggestively named.
- I would like to know as well. So far I have only seen it contain 0s, possibly an abandoned file...? --Pi Masta 17:04, 9 July 2007 (PDT)
I'm thinking that the file XBASES.DAT handles what base the aliens will attack. It's 48 bytes long which divides into 8 nicely. Normally the file has all zero's in it but on my saves just before a Base attack there's one byte set to 1 --Pi Masta 17:04, 9 July 2007 (PDT)

Retaliation 3/0,1 (base not found)

These do not land.
eight turning points, leave.

One thing i've noticed that might help: searching Battleships on retaliation missions tend to overfly the base that they are looking for. This could be just coincidence but i've seen it happen a few times. Could the turning points be related to the location of the base?

Hobbes 16:12, 6 January 2007 (PST)

The Retaliation 1/0 I observed was zigzagging across where I had done two shootdowns, so that's entirely possible. The 1/1 was more generalized.

Zaimoni 6:48, 7 Jan 2007 (CST)

Zaimoni, anything you can do to predict where and when something might land, given your insights, would help. Are there specific speeds and/or distances associated with each leg? I guess it's less relevant with Terror (aimed at a city) and Retaliation searches, and Supply is often (always?) aimed at an existing base. But with Research it could be useful. Players sometimes want to catch a UFO just as it lands, to save flytime/fuel and/or daylight. In my experience though it's pretty random and basically hard to predict, even with reloading, as you say.

Could you benefit from a logger program that collects data overnight, or does it seem so highly variable that it's anybody's guess when a Research might land? - MikeTheRed 17:09, 10 January 2007 (PST)

Sorry for the delay...I must have had a work schedule spike that lasted a few weeks. (I don't have email notification turned on, just a URL checklist that includes this site.) I just started actually playing again, so had new early-game data.

There is no consistent distance, just the sparse grid of valid points. Landing times will not be predictable from a savegame until the landing site is the next waypoint. Retaliation missions may not be consistently random in the choice of these points. Speeds are consistent within UFO type: there is an "incoming" speed, a "near waypoint" speed, and a "between waypoint" speed. The current waypoint is consistent between saves.

Not sure about logger yet (have AutoHotKey installer on my system, but my AV is very unpredictable in when it runs). Some sort of "slice" logger would be of limited use here. I'm also considering a range test run to pin down the exact duration ranges on MISSIONS.DAT