Talk:UFO Detection

Removed sentance suggesting using the graphs to locate UFOs general area being a 'borderline exploit', after all your base could well come with a telephone so governments can call and tell you that their civilians have been reporting UFOs flying over their terrority. It would seem to be a fairly essential way of defending the rest of the world in the first month or two while you get other bases set up to detect more aliens anyway, otherwise your interceptor would have almost nothing to do with your piddling little single radar covering about 5% of the land surface, and missing half the UFOs that wander over that terrority for 10-12 hours anyway (let alone missing anything fast moving 90-95% of the time). Its not like it is something you want to be doing for long anyway, as its fairly fiddly to keep checking the graphs every hour or so for new contacts.

--Sfnhltb 15:01, 26 February 2007 (PST)

Added a load here - the detection rates are based on the values in BASE.DAT and some hex editted trials of game saves that bore out that the values there seemed to be percentages. As this value seems to not get increased by building extra radars, this would seem to indicate the suggestions that more than one of each type are useless, but the combo of 1 short/1 long is valid (until hyperwave of course). The range of short radars was done by testing at what point on the map UFOs could get to without disappearing (factoring in that they almost always disappear only when each 30 minutes is up, so positions between those times dont count as part of the range). This assumes that the point at which you lose contact is based on the same range as you can spot them, but I think this is a reasonable assumption.

Note I tried a few things to try to disprove these hypothesis, such as building 20+ large radars in all 8 bases - no clear increase in detection rate over a dozen or more reloads of the same time period (ran for about a day, just to let the existing UFOs move about, and see if any more were seen compared to a similar amount of runs with just 1 radar). Changing the BASE.DAT detection rates for short/long to 100 each saw an immediate increase in detection rate, so it seems these values are what is used by the geoscape. They reset when you complete a build of any new facility it that base, so you could have 100% radars if you wanted, but only if you dont build anything new (or remember to go back and re-edit any time you complete something). Of course if you are doing that, why not just edit a hyperwave decoder in...

--Sfnhltb 18:55, 26 February 2007 (PST)

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We really need to look at the Small and Large radar pages. Simply put, much of the information in-game doesn't agree with game file analysis. In fact, it normally is in direct disagreement with both game files and the Official Strategy Guide (OSG). Here's a table I drew up a long time ago to show the differences. Please note that the detection ranges listed in the OSG are 1/5 that of in-game, so we can back-calculate it's hypothetical range of 480.

Radar	Det. %	Det. Range	Sweep Rate
Small (in-game)	5%	300nm	10
Small (game file)	10%	1500nm (OSG)	30
Large (in-game)	5%	450nm	10
Large (game file)	20%	2250nm (OSG)	30
Hyperwave (in game)	100%	? (480)	DNA
Hyperwave (game file)	100%	2400nm (OSG)	30

--Zombie 19:35, 26 February 2007 (PST)

I think they now match up mostly to what you have above, with a couple of differences being as they have been calculated experimentally (and fairly roughly) they show some level of deviation, and also there definitely seems to be an extended tracking belt from my tests that is not covered in the table, although its exact size is open to question a little, but it certainly seems to be larger that 1500 for Small Radars.

--Sfnhltb 21:43, 26 February 2007 (PST)

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I might have missed some of the discussion, but do UFOs leaving the tracking zone disappear and reappear on the half hour? I've always had the impression that they just dropped off and reappeared instantly the moment they cross into or out of the tracking area's borders.

Can we also work the phantom radar bug somewhere in here? The only reference of it so far has been on my talk page for yonks. I could never think of how to slip it in.

- NKF

One thing you might want to check with that bug is that it might go away when you complete any new build on the site, not just a new radar - as when I was playing with setting the radars to 100% detection rates, those got reset with a new build, whether it was another radar, or an alien containment facility (to take the example I happened to test).

If the game files suggest ranges of 1500 miles for the small radar, it then opens the reverse question - in practise I have definitely reguarly had previously detected UFOs move out to larger ranges than that, and wander around for an hour or two without dropping off, which happens almost always once they are outside something closer to 2000 miles. Maybe the detection is fixed to the number in the files, and tracking is an extra 33%. This would seem to make it less likely there is a size of UFO factor (although I guess small or medium might use it at 100%, and battleships might have a >100% factor to increase the range they can be detected in just as easily as having a reduction applied to the smaller craft). Cant really think of any decent way to test this either way though.

--Sfnhltb 21:29, 26 February 2007 (PST)

Note also that as far as my testing and experience goes, I dont think the UFOs disappear no matter what range they are at, except when the half hour check comes up. One example I saw recently I had an interceptor chase from my only base in Budapest (short radar), I called off the pursuit in central africa (maybe 3000 miles south, well out of short radar range) while the craft was a shortish distance away, but not catching it up. This was at around 20:35, at 21:00 with my craft nearly at the base, the UFO finally disappeared - it had gone past South Africa on the way to Antartica by this point.

I have noticed UFOs disappear off the radar twice in about 40 or 50 tests at other times (and there might well have been more when I wasnt paying attention), but its fairly rare for that to happen, and I would still suggest it is just them ending the mission, rather than anything different happening with the detection/tracking rules.

--Sfnhltb 21:40, 26 February 2007 (PST)

Well, blow me down, you're right. The stats are reset on the construction of any new facility. Mind you, the thought of testing this with non-radar modules never crossed my mind when I discovered this little bug. It seems to only affect the base where the module was constructed, so it won't change any existing module-less radar effects for other bases.

This certainly reduces the lifespan of the phantom radar a bit. I suppose it can still be useful in two situations, the first is when you're waiting for a new radar to be built but you need the space. The other is once you've finalised the base and no longer want to make any changes to it.

Heh, I've always said that this game often surprises you no matter how much you think you know it inside and out, and that still holds true.

- NKF

Heh, trying to reverse engineer the exact rules and behaviour of a game, especially when you have to factor in both bugs, potentially incomplete cheats being used to do some of the testing in a reasonable time frame, hidden factors, and so on, is always going to be liable to throw up surprises.

I get the feeling the radar bug is because of the same thing, it checks for range on new builds, but not on destructs or anything else. You could kill off a small and large radar, plus a hyperwave, and have all three continue working as long as you never complete a build again on that base. Of course one of the main reasons you might remove such facilities is to free up space, so its not much of a cheat (except for the maintenance savings, which is trivial in any normal game I have played) unless you directly hex edit (or equivalent) fully built facilities over the top of them rather than building them in game, so you have to cheat to make it a really effective cheat...

--Sfnhltb 22:10, 26 February 2007 (PST)

Losing Contact

If the UFO simply goes beyond your tracking range it will just vanish. If it circles around and re-enters this range, it'll reappear instantly.

I am reasonably confident this isnt the case, see above notes for how far they can go at times and still not be lost of radar. What might happen is that a detected UFO that leaves covered airspace disappears at the end of a 30 minutes segment. It might then 100% reappear 30 minutes later (or at any later check point) if it comes back inside any of your radar ranges - i.e. you dont have to reroll a 10% chance for a small radar to respot it when it comes back.

This would make a lot of sense - it could explain why craft radar seem so good at spotting UFOs, i.e. because you usually send craft after an already spotted UFO. This would suggest that craft might not be so much better at spotting UFOs (they might be anyway) because of this effect. If this model of detection/tracking behaviour is correct it breaks down like this:

• Previously undetected UFOs, use the basic range of 1500/2250 for radars, and you must roll your 10/20/30% chance to spot it every 30 minutes
• Previously detected UFOs, inside the (33%) extended tracking range at a 30 minute tracking checkpoint will always stay detected, no new roll is needed
• Previously detected UFOs, outside the extended tracking range will stay on screen, no matter where they go, until the next 30 minute tracking checks are made
• Previously detected UFOs that have since dropped off track due to range, will reappear if they are in range of any radar systems extended tracking range when any tracking check is made
• If a UFO ends its mission, it will immediately disappear off track from anywhere, this can happen at any time (I think)

Anyone see any holes in this, or ways to test things that havent been confirmed - quite a bit is speculation, as I cant think of any way to know what the UFOs are actually doing except while they are detected. Maybe a two base setup with one Hyperwave Detector, and the other base with radars can do something here, wait for a UFO to come in range of the Hyperwave but with a mission to go near the Radar and see if that confirms the 100% repick up (assuming it disappears in between the coverages at the 30 minute checkpoint as expected). Could take a while to find a craft to match that profile though, but once you do could repeat run a few times to confirm the behaviour, or prove that I am talking nonsense, as applicable.

--Sfnhltb 22:04, 26 February 2007 (PST)

Previously detected UFOs that have since dropped off track due to range, will reappear if they are in range of any radar systems extended tracking range when any tracking check is made

I am rethinking this case, and I think it may well be possible that previously detected UFOs can be reacquired at any time, I will have to try and check the clock when this happens sometimes, but I think it makes sense otherwise craft would have more trouble than they do reacquiring with their small radius if it only applied every half hour. It could be either though, will just have to see in practise.

--Sfnhltb 11:20, 27 February 2007 (PST)

I think I've seen this. It's been a few months since I've actively played, but I seem to remember seeing UFOs disappear and reappear while dancing around at my radar's maximum range. No "redetection" message was seen, the X just showed up again, briefly.--Ethereal Cereal 14:58, 27 February 2007 (PST)

About the UFO's disappearing at anytime, don't they take off? Kind of like they would in reality. Seems to me when they start traveling in a straight line at top speed and I check their altitude it's 'VERY HIGH'. They don't disappear very fast usually takes a good hour while in this state to finally disappear. Only exception to this are Terror Ships that make terror sites, which I think they go away upon making the site.

I know the UFO's do this behavior when coming in to the earth (only in opposite of course). They start out Very High at max speed traveling in a straight line and then abruptly change and (usually) throttle down once they are in the region. I haven't actually tested any of this, just my observations in game. Usually if I have an interceptor going for a UFO, and that UFO goes to max speed I check it's altitude and if it's very high and moving in a line (usually out to sea, or at least out of the region I spotted it), I figure it's taking off and the interceptor can't well... intercept, so I call it back. Rather have it ready for the next UFO sooner, than chase it and lose it over the Pacific a few hours later only to have to wait hours for it to get back and refuel.

--Pi Masta 20:25, 1 March 2007 (PST)

Provisional graphic

Based on measurements done on the surface of a globe and my assertion that tracking range = 1.5x detection range (see Talk:Small Radar), here is a provisional range comparison:

I no longer believe that there is a difference between tracking and detection ranges -- the difference between the two is caused by a combination of UFOs moving at high speeds and the fact that "detections" are only updated every half hour, as Sf theorized. Updated graphic:

• Yellow = Detection range of a craft (1500nm diameter)
• Green = Detection range of a Small Radar (3000nm diameter), also maximum "base detection" range for craft
• Blue = Detection range of a Large Radar (4500nm diameter)
• Red = Detection range of a Hyper-Wave Decoder (4800nm diameter)

It might look as though a Hyper-Wave can track UFOs nearly halfway around the globe, but that is due to foreshortening at the outer edge of the globe. 7200nm is exactly 1/3 of 21600, the diameter of the Earth in nautical miles.--Ethereal Cereal 02:17, 27 February 2007 (PST)

Seems pretty reasonable to me, matchs up to the sort of places I would expect to see, track, and lose UFOs in each case. The craft radius initially struck me as looking a bit large, but I think this is because its fairly common for your craft to be off to the sides of a screen, which especially when you are zoomed out will make the distance between craft/UFO look shorter than it actually is if you were to center on them.

--02:53, 27 February 2007 (PST)

These ranges are substantially correct for Hyperwave Detector and Large Radar, for my standard starting base (Base Nigeria). Hyperwave may actually be a bit larger, but not much.

--Zaimoni 10:06, 27 Feb 2007 (CST)

New Version

Looks really good - only thing I am tempted to move out is the Radar Detection ability table, maybe move it to BASE.DAT and link to it there in case people are interested?

--Sfnhltb 21:56, 1 March 2007 (PST)

Fair point; I brought it in because it was the centerpiece of NKF's original article, but ultimately it's source material, and probably too under-the-hood-ish for this article. I moved it to base.dat.--Ethereal Cereal 22:38, 1 March 2007 (PST)

Effectiveness comparision

Can someone check this, not totally sure whether its worth adding here or not, but first want to ensure its correct:

Large Radars have 150% of the radius of a small. Therefore they cover 225% of the area (using basic trig, but based on a plane, not sure if that alters when considering radius over a sphere, it might well do), and then it has 20% instead of 10% chance per half hour of finding a UFO (assuming this is not modified by size). Using both these we can determine that adding a large radar to a small radar increases your chances by 450%, conversely adding a small radar to an existing large radar increases your chance by about 22%. Of course both is better, and some coverage after 12 days may be better than good coverage in 25 days for some situations.

--Sfnhltb 07:57, 6 March 2007 (PST)

I'm no mathematician, but the 225% applies even though it's overlaid on the surface of a sphere (a "simulated" one at any rate). I'm not sure if comparing the pure numbers paints a correct picture, though. Adding a small radar is probably less effective than 22%, as there's a good chance a UFO will be detected at long range before it enters the "small radar" radius. Another factor is, "where do the UFOs hang out?" If your large radar's area is partly over water, some of its detection chance is wasted, since UFOs tend to zigzag over land masses.

The amount of time a UFO spends over a continent is a factor too: either radar will approach 100% detection the longer the UFO stays in-range. And then there's the "MUFON" approach you described, and craft-based detection, which reduce the importance of either radar. Nonetheless, large radars seem a lot better than small.--Ethereal Cereal 15:42, 6 March 2007 (PST)

Yes the main advantage of the Large Radar over the Small is for passing traffic - for example if early in the game they have targetted a neighbouring continent then it helps more, if they are aiming at a spot where you have only a small radar you will still get them most of the time due to the amount of chances they give you. Of course its great on the way in, if they have finished up and are heading out then you scramble an Interceptor for no purpose in many cases. --Sfnhltb 15:55, 6 March 2007 (PST)

Raw base detection?

Ok I'm pretty sure I saw a new base - with no detection facilities - detect a UFO. It was a new detection (not previously detected). The UFO was very close to the base, probably in the 750 nm band. It was not a hyperwave type of detection message. No aircraft at or anywhere near the base. No other base in range. The new base was polar (Antarctic).

Does this sound plausible? That a base has the same raw detection ability as an aircraft? Anyone seen any evidence for anything like this?

Spike 17:49, 4 March 2008 (PST)

I've only ever seen this effect with the phantom radar trick, where you dismantle a radar in a base, but the radar's effects stick until any new base module in construction at that base gets completed. I'm not sure how it would work with a brand new base, since the detection abilities of the base should be set to 0S, 0L, 0H. Do you still have your game? One way would've been to the save file for that base's radar stats to see if the short or long radar settings have values in them. - NKF 20:42, 4 March 2008 (PST)

The other possibility is the random end-of-the-month check if X-COM agents found the base. If you're clicking very fast during the end-of-month performance evaluation, you could probably miss it. Arrow Quivershaft 23:58, 4 March 2008 (PST)

To clarify, it was a UFO that was detected, not an alien base. There was detection popup event, the radar type not the hyperwave type. No radar or hyperwave system had ever been constructed at this base (though they were under construction). They had not finished building. I will look for save files. Is it BASE.DAT I need? If not, I guess it is an easy theory to test: just build 8 bases with no radar, let the game run, and see if any UFOs ever get detected. Spike 01:19, 5 March 2008 (PST)

Be interesting to see the files. But why build any radar at a base if you're building a Hyper Wave Decoder? It's a waste of money both building and later with the paying for dirt bug. HWD has (just barely) longer range than a Large Radar and detects 100% of UFOs in range; Large radar gets a 10% chance to detect any UFO in range per half hour, and Small Radar gets a dismal 5% chance to detect any UFO in range every half hour. Arrow Quivershaft 15:37, 5 March 2008 (PST)

Why build Small Radar?

@AQ, I often build a small radar when I start a new base, even when I can build Hyperwave Decoders. I often build both, and the same thinking applies to building Small plus Large radar at the same time. The reason is the shorter build time and the extra 13 days of detection that gives -even one extra intercept will more than repay for the cost of the Small Radar. Once the Hyperwave is online, the radar can be replaced (mitigating the phantom payment bug). The "payoff" from the extra intercepts can be diplomatic, technological & in terms of experience gain, as well as financial. This is why this UFO Detection topic is so important: Detection is the key to all other progress. There are tradeoffs as it can make the base less defensible if you don't want to delay building the HW decoder (depending on your Base Layout strategy). Spike 23:44, 5 March 2008 (PST)

There is also the fact that if you play well enough that you will often reach a point where you hardly even notice that you're paying for dirt should you not recovering the used module lot. Even if you don't value its not-too-shabby radar abilities (not too great for fly-overs, but those that hang around get detected easily enough) the defensive use of the module itself is handy, being an empty octagonal room where no units on either side get generated. - NKF

Raw Base able to Detect? Not.

I did the test run of 8 bases and I didn't detect any UFOs at all. I ran until the end of April. I think with the various "center on UFO" for both detection and intercept, I got confused about which polar base made the detection: it's hard to recognise the map outlines at the poles with the country names and borders off. That's my excuse anyway. So the UFO was probably in fact detected by my other polar base, which had recently built a Small Radar - for the reasons just stated! Spike 23:44, 5 March 2008 (PST)

Playing With No Detection

It was interesting to see how the game progressed with no detection at all (not even using Patrol or in-flight aircraft for detection). It went surprisingly well. I was able to maintain a positive score and increase funding simply by responding to terror missions (very much in the spirit of the intro movie!). I did permit myself to send a Skyranger to find an Alien Base after South Africa defected at the end of March. I guess I should've waited for the XCom agents to find it. Technology and manufacturing progress was difficult, especially as there was no Elirium and very few alloys. I had to make my own Alloys which is normally not at all cost effective. Surprisingly there were no Base Defence missions, probably because I was doing no Intercepts. They probably would've happened eventually. I imagine finances would be very tough but I didn't test the economics - I just started with $1 billion for the purposes of testing the "raw detection" theory. Playing without detection would also mean taking maximum advantage of every encounter (terror or base msission) to extract maximum score, recoverables, and experience. Spike 23:44, 5 March 2008 (PST)

Thinking about this more, the economics of playing "No Detection" would be very tough. Largely reliant on goverment funding, you'd need to run a very lean organisation. Probably just one or max 2 bases with Skyrangers only of course. Would you ever get any Elerium or even just one Alloy, doing only Terror, Base Defence and Base Assault missions? If you did, could you afford the scientists or engineers anyway? Probably small teams would be OK. For Base Defence, numbers of soldiers would have to make up for lack of technology. With XComUtil technology and research rules it's particularly challenging - and cool - artefacts and live captures become incredibly precious and important. The breakthrough point of course would be getting an Alien Base to milk (preferably in a low-funding nation). From then on (March/April on Superhuman?) things start to head back on track to what we would consider normal, at least from a cash point of view, if not technology. I'm not sure you could win this game as you would not get Elirium to build the Avenger for the Cydonia mission. And as you are only reacting to Alien Bases, even if you destroy them all your funding nations would eventually go over to the Alien side. Is it possible to survive on plunder alone, with zero funding? Spike 04:21, 6 March 2008 (PST)

A legitimate reason to build the Small Radar which I had not thought of. In any case, yes, it is possible to win on base raids, since Alien Bases do have a module in them that spawns small amounts of Elerium. In fact, you can beat the game by assaulting a single Battleship, provided you bring back three aliens(Commander, Leader, and other), an Alien Alloy, at least one Elerium pod, a UFO Navigation, and a UFO Power Source. I've done so several times. :) And I'm not surprised the aliens weren't attacking you; Alien Retaliation missions are triggered mainly when you REALLY piss the aliens off by being quite successful in interception and recovery. Arrow Quivershaft 07:58, 6 March 2008 (PST)

Interception. Hard-verified triggers of Retalation acts include shooting down UFOs (immediately, and furthermore the durations are so conveniently non-random), and something that happens start-of-game that guarantees a starting act of Retalation that I've personally never seen in 100+ games (CE), but NKF has fairly reliably. I do know it's not just hacking in the Hyperwave Detection stat, as that doesn't do it for me.

Battlescape UFO recoveries don't trigger Retalation acts directly. It is possible that various factors (such as total score) bias the probability of creating a Retalation mission, but as I do in vivo testing it's a bit hard for me to get adequate numbers to check such things. I do know that I get far more Retaliation acts than the easy probability estimates would suggest. Zaimoni 10:13, 6 March 2008 (CST)