Talk:UFO Detection

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Questions, Comments, etc

re Alien Base Detection

"All X-COM craft are also capable of detecting alien bases. In fact, this is the only way to discover alien bases: they will not show up on any base radar, including Hyper-Wave Decoders. (However, "X-COM agents" will sometimes report the discovery of a base during X-COM's Monthly Report; see Locating an Alien Base.) In order to discover an alien base, an X-COM craft must patrol within 1500 nm of the base's location. The nearer the craft, the sooner the base will be discovered. Patrolling immediately above a base will reveal it almost immediately; patrolling 1500 nm away, the base may take one hour to discover, or several hours.

Bases can only be discovered by patrolling craft. An X-COM craft could fly over an alien base repeatedly and never discover it until it began patrolling in the area."

Are you certain? I've seen my newly built base detect an alien base right next to it without any crafts nearby. -amitakartok


General Discussion and Editing Comments

As I was responsible for making this page a lot lengthier recently I thought I would try to reorganise it thematically so it is easier to use and navigate. I hope that's ok with everyone. Spike 10:37, 8 March 2008 (PST)

Removed sentence 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)


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%300nm10
Small (game file)10%1500nm (OSG)30
Large (in-game)5%450nm10
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)


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)

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)

I hope those changes are OK. Once we are sure that the aircraft range is 600nm and not 700 or 750, can someone change the graphic to show a 1200nm radius? Spike 11:02, 9 March 2008 (PDT)

Did you try hex-editing the executable?
.text:004591E9 cmp     ax, 0C8h
is supposed to be the check on distance between the xcom ship and the ufo. If you put something huge and the ship starts detecting stuff on the other side of the planet, then we'll be sure... Seb76 11:10, 9 March 2008 (PDT)

Yes I checked and you were absolutely right. It's proven, so we should change the main page. I wish I knew how you found that needle in a haystack though! Spike 16:16, 9 March 2008 (PDT)

Proposals for changes

I propose that we change the main page to state without caveats that the aircraft detection range (vs UFOs) is 600nm, 200 range units. This is because I have used Seb76's patch information to patch those bytes (set to 200) and they definitely control airborne detection range. Spike 16:22, 9 March 2008 (PDT)

Also, would it be good UFOpaedia etiquette for me to move a lot of my musings over to my User Page rather than here? Spike 17:20, 9 March 2008 (PDT)

Detection

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)

Detection Ranges - 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 System), 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:

Detection and tracking ranges.png

  • 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)


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)

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


Airborne Detection ( the Skyranger AWACS Platform)

Another detection option, and one which may speed up your initial intercepts, is to hire a Skyranger and put it up on AWACS duty. Same price as a Small Radar, and it arrives in 3 days instead of 12. That's an extra 9 days of detection, albeit on one quarter of the area coverage (750nm radius vs 1500nm radius). I don't think we know for sure the detection percentage for aircraft, do we? The refuelling cycle means the Skyranger will be off-station and off-air about 1/6th of the time. And the Skyranger costs a LOT more in maintenance in following months (25x even taking into account the facilities cost bug). But the Skyranger also has many other uses. So as a start-of-game or start-of-new-base strategy it might be a useful idea. I guess the question is, how many extra intercepts do you get in those 9 days? Even one extra intercept makes the Skyranger "free" and gets you score, experience and technology progress - plus vital extra cash.

Spike 10:52, 7 March 2008 (PST)

In fact, it is claimed in this article that aircraft detection percentage is 100% within their radius. This in theory makes them 2.5x more effective than a small radar, at least for UFOs that don't linger around more than one detection interval (30min). Spike 11:47, 7 March 2008 (PST)

Now consider a moving Skyranger. In theory, in addition to its base 1.767 million sq n mi circular swept area when stationary, a moving Skyranger at 760 knots adds another 380 x 1500 = 0.57 million sq n mi rectangular swept area, a further one third. With 100% detection, in theory this makes the Skyranger 3.3 times more effective than the Small Radar - 2.32 times more effective after allowing for the "duty cycle" (time airborne vs refueling) of the Skyranger (70%).

And factoring in the higher cost of the Large Radar, a moving Skyranger is ever so slightly more cost-effective than a Large Radar - for the first month of service at least. In subsequent months the cost-efficiency of hired aircraft plumments due to their 100% maintenance costs.

And if you also factor in the longer build time of the Radars vs. short aircraft delivery times, the Skyranger is 4 times as efficient in the first month of the game than a Small Radar and 3.4 times more efficient than a Large Radar. Factor in the purchase cost as well as the build/delivery time and the Skyranger even beats a Hyperwave Decoder - by a factor of two!

Hurrah for Skyranger AWACS!

Factoid: The breakeven point when (theoretically) a Large Radar will have generated more intercepts than a moving Skyranger is 63 days after purchase. Spike 14:30, 7 March 2008 (PST)


Problem is, that second Skyranger requires a Hangar, and a Hangar takes 25 days to build...longer than a Large Radar! Of course, you could sack an Interceptor in order to free up a Hangar, but then you risk having no interception capacity if two UFOs come in quick succession(because you can't launch the Interceptor while it's refueling, rearming, etc. Missiles take a LONG time to reload!) Furthermore, my tests imply that aircraft only can detect things when they are STATIONARY. Not when moving, unless there's already been a lock established on the UFO. Arrow Quivershaft 14:34, 7 March 2008 (PST)
Very good points AQ. Not just the $200K but the 25 days for the Hangar. So we need to factor that out except for the special case of the beginning of the game. I was taking it from UFOPaedia.org that aircraft can detect UFOs (but not bases) while moving. But your experience suggests they can only re-acquire previously detected UFOs while moving, and if that's true it considerably lessens their effectiveness. Also when I was looking at moving vs static (patrolling) aircraft I forgot to consider that the duty cycle is worse for moving aircraft (if conventionally powered). Taking into account the duty cycle, the figures including both the patrolling (P) and moving (M) aircraft, relative to a small radar = 1.00, are:

Aircraft vs Radar Detection Efficiency (Table)

This table has been updated to reflect 2 considerations:

1. Looks like craft detection range is 600nmi not 700 or 750 nmi (thanks Seb76).
2. Since detection checks are only every 30min, 'sweeping' other areas for the first 1-29 min does not help at all. All that matters is what is in range on the 30th minute, it seems.

(See spreadsheet Detection Chart) Spike 11:19, 9 March 2008 (PDT)


Platform Duty cycle Vs Sm. Radar
Skyranger P 85% 1.35
M 70% 1.12
Interceptor P 62% 0.99
M 43% 0.69
Firestorm P 60% 0.95
M 60% 0.95
Lightning P 61% 0.97
M 61% 0.97
Avenger P 62% 0.98
M 62% 0.98
Small Radar 100% 1.00
Large Radar 100% 4.50
Hyperwave 100% 25.60


The "duty cycle" consideration only applies to long-term surveillance, which is assumed in the numbers above. For a quick-reaction situation, all aircraft are 1.60 times more effective than a Small Radar. On the other hand, a Small Radar will eventually detect a UFO at between 600 - 1500nm, which the aircraft will never detect unless it strays closer. So the effectiveness numbers above are most relevant for detecting passing traffic.

I guess another drawback of aircraft vs radars is that radars rarely get damaged or shot down. On the other hand you can't deploy a radar to a point half way round the world in 12 hrs. And, unlike radars, aircraft detection is (probably) cumulative. That would be interesting to test, anyway. Spike 17:11, 7 March 2008 (PST)

It should be noted that I meant keeping a radar bead on a detected UFO even after it leaves ground radar range, not redetecting a UFO you've lost contact with(although I think I agree that aircraft radar is close to 100% efficient). The strength of a Hyper-Wave Decoder is twofold; the 100% detection is useful, but the ability to know WHAT the UFO is doing and WHERE it's going to be doing it is even moreso! If you know where the UFO will land, you can launch a UFO Ground Assault instead of a UFO Crash Recovery. And you can get a good guess on terrain type. HWD also tells you what ship it is(so you know what to expect unless it's a Small Scout or Battleship which can be found by process of elimination) and what aliens are staffing it. This is useful if your strategy for Harvesters and Battleships involves blowing alot of holes in the walls, whereas you consider Blaster Bombs overkill on a Medium Scout. As well, knowing WHO you're up against helps you bring the right equipment to fight; put away Incendiary vs. Snakemen, AP vs. Mutons...and the tactical advantages are nice too. It's really quite nice to know that the Terror Ship you just shot down was crewed by Snakemen so you're using anti-Chryssalid movement patterns, instead of finding out the hard way when one of them rounds the corner and zombifies 4 soldiers before you can do anything! Also, if you're willing to cheat, you can use the Infinite Fuel exploit to keep those Firestorms, Lightnings, and Avengers in the air for a long time! Until they run out of ammo, really. Arrow Quivershaft 17:22, 7 March 2008 (PST)

In general, we end up using a combination of the strengths of the ground based radars and the AWACS system to cover the weaknesses of the other. Standard radars are stationary and don't spot UFOs immediately, but they are operating all the time and have little overall maintenance costs. Ships can fly out to remote areas and investigate possible activity sites. More importantly, they are for spotting bases. Ship radars get the extra benefit of being the only radars that can reveal alien bases (well, that and the Mutual UFO Network that occasionally decides to help out). Ships cost more to maintain overall, but that's expected since they have a larger number of duties to perform. Of course, relying on just one type of radar detection method is a nice enough challenge. - NKF 17:34, 7 March 2008 (PST)

Good points there AQ on the many benefits of HWDs and NKF on the benefits of flexibility. Spike
I generally think it's a good idea to decomission one interceptor in favor of a second skyranger. Reasons can be found here. --Schnobs 08:31, 9 April 2008 (PDT)

Aircraft-based detection while moving?

AQ above has done some tests that suggest only patrolling aircraft, not moving ones, can detect new UFO contacts. So the theory is that moving aircraft can re-acquire previously detected UFOs but not new contacts.

I tried testing this but it's tedious in the extreme as you have to spend a long time managing the aircraft if they are not on Patrol. I ended up doing racetracks around the US and Japan while MUFON (graphs) was showing high alien activity in those areas. I only managed to do a few days, it was tedious. However I did generate one contact. An aircraft took off from NeoTokyo and immediately acquired a Landed UFO nearby in Hokkaido. This was a genuinely new UFO contact as in this particular saved game I have never had any radars and no aircraft had been on patrol for months (this was my "No Detection" test rig). Other than that I did not get any actual airborne UFO contacts. Maybe landed UFOs have different criteria? But thinking about how long you sometimes wait for a contact even with multiple HWDs, weeks or more, the absence of a contact over 2-3 days isn't much evidence.

What my test did point out is how tedious it would be in practice to carry out airborne surveillance using moving aircraft rather than patrolling aircraft. The micromanagement just isn't worth it, except perhaps very early in the game. Spike 04:58, 8 March 2008 (PST)

Maybe the game detection logic does not check for detection while an XCom aircraft is moving. It would certainly be simpler to program and lower CPU overhead so they may have done it that way. For example when my aircraft launched from NeoTokyo it may have momentarily been considered "stationary" before moving off to its waypoint. Alternatively maybe it acquired the landed UFO only because the UFO itself was stationary.

And it's quite possible that even if the detection logic does operate while the aircraft is moving, that the game logic ignores the 'swept rectangle' during movement and only considers the radius around the aircraft at the instant of the detection check. In which case all the advantage I was theorising about for moving surveillance aircraft is just that, theoretical. I would not be unhappy with that as to be honest it makes sense for the detection ability of moving aircraft to be at least reduced, if not nil. Probably unless I can found any empirical evidence of a 'swept rectangle', we should assume the detection area is an instantaneous circle and not a sort of ellipsoid smudged out over 30 minutes of flight path. My guess would be that the game logic does the detection 'instantaneously' based on the position every 30 minutes. So then the only advantage of a moving AWACS (assuming they can detect anything at all while moving) would be if you want to scan lots of different areas, briefly. Given the presumed 100% detection rate for aircraft, this would be useful in a lot of situations though.

Until any of this is proven I would stick to using aircraft in Patrol mode, we know that works. The figures in the Aircraft vs Radar Effectiveness table above should be valid for the 'P' (Patrol) mode at least.

Spike 10:53, 8 March 2008 (PST)

I was going to come on and report that I had documented an intercept by a moving aircraft. But the evidence is still ambiguous, the UFO may have been in the outer limit of my Small Radar - I'm checking the screen shots. Next time I'm going to erase the Small Radar with a base editor at the start of the (test) game so I can be sure all intercepts are from aircraft. Spike 15:40, 8 March 2008 (PST)

Well this is all very interesting. I repeated the same test game but restarted 4 days prior to the original intercept (Jan 5th) and used a base editor to turn my starting Small Radar and under-construction Large Radar into under-construction Missile Defences. A day later they completed building and so that eliminates any detection capability, radar, or phantom radar in my starter base right? As MUFON was full of reports from Siberia I started zipping all aircraft out there one at a time and soon enough, at 2:59 in the morning of the 9th of January, Skyranger-1 en route to Siberia (and a long way off its waypoint) intercepted UFO-3.

Somehow I don't think UFO-3 had been previously detected 4 days earlier and was still hanging around. I think this is proof that XCom aircraft can detect new, previously undetected UFOs while the XCom aircraft are in flight and not yet in Patrol mode.

I have saved off the game files if anyone wants to check BASE.DAT etc to confirm. I also have some simple screenshots that tell the story.

Spike 18:12, 8 March 2008 (PST)

Detection Algorithm and Ranges

FYI, when performing UFO detection the engine skips crafts for which bit0 at offset 0x64 (in CRAFT.DAT) is not zero (most likely a flag linked to patrolling state of the ship). The detection rate _is_ 100% if the craft is less than 200 units (using the same internal units, hyperwave range is 800, long range radar is 750 and small radar is 500) from the UFO. Seb76 15:04, 8 March 2008 (PST)

OK, bit0 @ offset 0x64 is definitely not a 'not patrolling' flag. Since it is set to 1 when a craft gets back to its base, and that fuel level is updated when it is 0, it is most likely a bit indicating that the craft is at home in its base. Seb76 15:39, 8 March 2008 (PST)
Thanks Seb, really interesting! And is that definitely 200 units for aircraft, ie 600nm, not 250 units / 750nm as stated elsewhere?
No doubt about 200, maybe you can try to patch this:
.text:004591E9 cmp     ax, 0C8h
and see what happens ;) Seb76 17:14, 8 March 2008 (PST)

Checked this and it works, you are right. How did you figure that one out? Amazing! By patching these values I was able to give my aircraft radar, and my starting Small Radar, global range (I did separate tests for each). This could be very useful for other diagnostic tests eg watching alien behaviour.

Hehe, it's a secret ;) While your at it, you can check the retaliation UFOs detection range:
.text:004594B9 cmp     ax, 50h
Seb76 13:04, 10 March 2008 (PDT)

Here are all the locations in Geoscape.exe / UFO_Defense.exe:


Platform Address Data bytes Hex Range nm
Aircraft 591EA C8 00 x00C8 200 600
Hyperwave 59237 20 03 x0328 800 2400
Lg Radar 5926D EE 02 x02EE 750 2250
Sm Radar 59278 F4 01 x01F4 500 1500


Patching "88 13" to these locations = x1388 = 5000 range units = 15,000 nm pretty much gives that platform visibility over the whole world. Of course Small Radar still only has a 10% detection chance per half hour.

Spike 16:01, 9 March 2008 (PDT)

Sounds like the bit 0 at 0x64 offset is an "airborne / at base" flag. It makes sense for the game engine to only do detection checks for aircraft that are airborne. And it explains my earlier result, when an aircraft detected a nearby landed UFO as soon as the aircraft took off (flag set to true).

So now do I have to re-do all my Aircraft vs Radar charts based on 600nm range? Ah well! :)

Spike 18:12, 8 March 2008 (PST)


While we're at it: base detection. For each xcom ship and each alien base, the probability of detection looks like 2*(25-distance/20) (or (500-distance)/10 +/- rounding issues). Of course if it is negative, it is just ignored. Seb76 18:28, 8 March 2008 (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)


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)
UFOPaedia.org offers mixed opinions on this one. Seems that from an Alien Base Assault mission we can definitely get Alloys, UFO Power Sources, and (from 1/2 the power sources) Elirium. But, can at least one UFO Navigation be recovered from an Alien Base? If not, it is impossible to research & build the Avenger, and so winning the game is impossible. I have not done enough alien base missions to know from experience if they ever produce a UFO Navigation from their stores. Spike 10:43, 6 March 2008 (PST)
The only UFO Navigations that spawn during a Alien Base Assault are part of the Base Command Console and need to be destroyed to finish the mission(and if you kill all the aliens instead, your soldiers will gladly do the job for you anyways!) So no, you can't get a UFO Navigation from a Alien Base Assault. You'll need to shoot down and capture at least a Medium Scout for that. Arrow Quivershaft 11:25, 6 March 2008 (PST)
Or maybe we have to wait for one to crash of its own accord, Roswell style, before we can unlock the mysteries of space travel... :) But would it be possible to "milk" the base - deliberately lose the mission - but still extract the Navigation from the control room? E.g. avoid killing all the aliens and reach the exit with it? Tricky. Or a soldier picks the Navigation item up before the aliens are all dead? Actually I don't know if a UFO Navigation can be carried. Spike 12:32, 6 March 2008 (PST)
No, UFO Navigation items cannot be picked up and carried, nor can UFO Power Sources or Alien Alloys. However, as for milking the base, you can raid the Supply Ships as they come, or you can do the extraordinarily dangerous alien base smash and grab. Arrow Quivershaft 13:00, 6 March 2008 (PST)
Without radars, you'd have to rely on the Skyranger's extraordinary ability to stay up in the air for yonks, and its own radar to pick up the supply ships. Really they'd be very cat-like, waiting for their prey and ready to pounce on them once they get close. As for the bases, what about completing the mission without destroying the tables? I don't think the game simulates destroying the base by destroying the tables once the aliens are all neutralised. But I couldn't say for sure. Also, if I remember correctly, aren't elerium pods generated equal to the number of power units in the base, minus one? (i.e. 4 power units = 3 elerium pods) - NKF 21:59, 6 March 2008 (PST)
NKF: Correct, you get 1 less pod than the number of UFO Power Sources spawned. Also, the game DOES simulate the destruction of those consoles if you win a Alien Base Assault by killing all the aliens. That's the only way I ever end base missions, because leaving any behind means I get no loot...and it leaves a bad taste in my mouth. If you kill all the aliens, the mission ends, and you're tallied up all the points for aliens killed, loot collected, units lost, and an additional +500 for "Control Console Destroyed." Arrow Quivershaft 22:50, 6 March 2008 (PST)
Sounds like with "no detection" you get "no Navigation" then. My topic here of "no detection" includes "no airborne detection" by Avengers or Interceptors. Almost as if the UFOs use some strange 'Stealth' technology unknown to Earth science. :) So that means no UFO Interceptions, no UFO Crash Recovery missions. It means being restricted to only Terror, Base Defence, and Alien Base Assault mission types. Base Assault are the only 1 of those 3 that will yield UFO Recoverables: Alloys, Elirium, Power Sources, Navigation. The Elirium can be milked by smash & grab, and the Alloys and Power Sources can be recovered in an Alien Base victory, but the UFO Navigations in the control console can't be recovered as victory destroys them. Those dumb marines just love to blow everything up. So maybe I need to hack the game and award myself 1-2 UFO Navigation with a base editor after completing a Base Assault victory. That might even be a good hack for a future version of XComUtil. After all if the console's Navigation globes are removed, dismantled and sitting in an XCom science lab, they can't still be controlling the base. Or can they?? <cue XFiles music...>

Spike 09:25, 7 March 2008 (PST)

By the way, my "no detection" scenario is now at the end of June and my government support is still good. A lot of time my funding is going up still! Still only one defected nation (where the Alien Base is) and still only one Alien Base that I am aware of. Does the presence of (8) XCom bases discourage nations from defecting and/or pulling their funding? The overall financial trend is good. I ran 10 tests that showed the average haul from an Alien Base Assault (Sectoid, Superhuman) - not including the precious UFO Recoverables which I wouldn't sell - is about $3.5 - $4 million for a perfect victory. This can be 'milked' indefinitely, which puts the game economics firmly back on course. Apart from the fact that in order to get Alloys and Power Sources to study you need to destroy the first base and then hope another one will come along soon. Prior to that point (2nd Alien Base) in the "no detection" game there are very few combat opportunities, just a terror mission every month or so. Experience gain is very difficult and it's important to make maximum use of each combat.

Spike 10:07, 7 March 2008 (PST)

I spoke too soon and as they say in Sectoid it's all gone a bit "piy't-t'ong". Come July and the Ethereals show up in force, in a LA Terror raid with 14 Ethereals and 9 Sectopods. The crack of lasers, the smell of burning flesh, and they're INSIDE MY MIND!!! It was all I could do to dust off from the LZ with a full set of frontal lobes. Sorry Los Angeles, your beautiful (and don't you know it?) but you're not worth the loss of XCom. I was totally outclassed. Not enough research to have Psi ability, not enough Elirium to build enough laser heavy weapons (XComUtil rules remember), and most important of all not enough experience. They took me apart, and ran missions aggressively all over the world. Funding and score collapsed overnight. I guess what I should've been doing is running Alien Base milking missions around the clock to build up experience, Elirium, hard cash, and a psionic leader to hand over to the interrogation boys.

Spike 11:15, 8 March 2008 (PST)

Multiple Radar Effectiveness Algorithm and Hack

Concept and algorithm

As we know, additional radars of the same type have no extra effect in a base, despite the presence of the Detection Strength bar which suggests a game design intention at some point to have some kind of extra effect. I like the idea that extra Detection Strength has some kind of usefulness, and so I propose this algorithm and a possible hack to make it (sort of) work:

Effectiveness of multiple radars=
100% - ((100%-Basic detection percentage)^(Number of radars))

So by example a pair of large radars (basic 20%) would have

100% - ((100%-20%)^2) = 100% - 64% = 32% detection per 30min interval

A group of 4 small radars (basic 10%) would have about 33% detection


(Clearly we can't use a linear algorithm, else 5 large radars = 5 x 20% = 100% detection and the Hyperwave Decoder loses most of its value. That would not be helpful for the game. Hence the geometric formula.)

OK one thing I haven't thought through is how to handle the fact that a Large Radar gives an additive boost to Short Range detection. What needs to be calculated is the total detection in each range band (short and long range), not for each Radar type. I think the solution is to treat give each Small Radar a short range detection of 30%, if and only if that Small Radar can be paired uniquely with another Large Radar.

Example 1: 3 Small Radars and 2 Large Radars.

Short Range detection = (100-(20+10))% x (100-(20+10))% x (100-(0+10))% = 56%
Long Range detection = (100-20)% x (100-20)% = 36%

Example 2: 2 Small Radars and 3 Large Radars.

Short Range detection = (100-(20+10))% x (100-(20+10))% x (100-(20+0))% = 61%
Long Range detection = (100-20)% x (100-20)% x (100-20)% = 49%

Looking at this, no one is going to build many Small Radars unless they are really in a hurry to get detection in 12 days instead of 25. It also makes me think that the 'phantom radar bug' is not a bad thing, as it allows you to 'upgrade in place' and improve a small radar into a large radar while keeping it in operation. That seems, well, not unreasonable.


From the way radar mechanics and UFO flight patterns interact, detection chance is high even with a single radar if the UFO hangs around in the area. The advantage gained from this multiple radar algorithm would mainly apply to fast moving UFOs that are just 'passing through'. Still, an intercept is an intercept and that means cash, score, experience and STUFF! I'm not saying whether it would or wouldn't be economically advisable to build extra radars but at least it would be an option, and open up some flexibility in base strategy.

Effect of multiple radars on detection chances

Please see this spreadsheet, I will wikify it if I get time:

How to implement

(Now implemented - see Implementation section below) Spike 09:53, 28 March 2008 (PDT)

This is a bit trickier. In principle what we need to do is edit the base file (BASE.DAT) to increase the detection percentage to the levels computed using the algorithm. The problem is that if we are to do this by XComUtil, values can only be adjusted when switching between Battlescape and Geoscape. Meanwhile, every facility build event in a Base will reset the detection percentage back to the default values. They will remain at the default values until the next combat.

I believe there is also a separate file (FACIL.DAT?)that stores the default values for detection and this offers an opportunity. Any changes to the default detection values probably need to be patched into the Geoscape executable.

The approach would be this:

1. XComUtil on re-entry to Geoscape checks for multiple radars in each base and applies the formula to each base individually to update its short range and long range detection stat.
2. At the same time XComUtil computes the average detection (short and long) for all bases (all bases having operational radar of that type) and updates the global default values to this average.
3. When a base builds something its detection values fall back from the previous 'specific improved' values to the previous 'average improved' values. Hopefully you weren't building a radar.
(But: would the game re-read the updated FACIL.DAT unless the Geoscape had been restarted? Probably not. In which case this is less helpful as the default detection values would fall back to a "historic average" that could be quite old. Probably still acceptable. Even if the update method is on-the-fly patching of GEOSCAPE.EXE after each battle.)
4. After next combat everything gets updated and reset again.

Obviously if this 'fall back to average' implementation was used, the 'smart' thing to do would be to give most of your bases the same radar configuration and definitely not to have one base with way more radars than others. Otherwise the results after a base had completed a facility build would be weird and counterintuitive until the next combat.

Apparently the Detection bars will increase currently if you build multiple radars. But would there be a way to scale the 'improved' detection bars so it showed how much improvement you had relative to a single radar. Eg show a Long Range Detection bar with length of 1.8 (32% / 20%) for 2 large radars. But it's by no means necessary.

Now, who is the current XComUtil maintainer? Spike 10:33, 7 March 2008 (PST)

I had a look at FACIL.DAT and there is nothing in there that could be the detection value, except maybe maybe maybe bit flag 1 in byte offset 0C, the so-called "Build flags" byte. So probably you would need to hack the Geoscape executable to set the default detection values. :( Spike 13:13, 7 March 2008 (PST)

Thinking about this a bit more, I don't think it's worth the effort of patching the executable repeatedly, just to be able to adjust the default detection values. It's enough just to be able to 'correct' the individual base detection values everytime Geoscape is reloaded. If people got annoyed that their detection was out of whack they could just reload Geoscape, no big deal. That kind of thing would be pretty easy to write as independent program if it's hard to get changes to XComUtil. Spike 11:26, 8 March 2008 (PST)

Possible Issues

WIth this algorithm it would be possible to get a combined short range detection probability of > 100%, since (we think from analysis of BASE.DAT) that short range and long range detection percentage is simply added together. That might have unpredictable results including maybe crashing the game - not good. From a game play point of view I don't think there's a problem in having a short range detection zone with 100% detection. You would need to build loads of radars to achieve it, about 4 Large and 5 Small, so fair play to you. Spike 15:48, 8 March 2008 (PST)

Actually, I doubt that the percentages are added together. What is more likely is that the computer rolls the "Small Radar Detection" chance against each UFO in range, and THEN rolls the "Large Radar Detection" chance against each UFO in range that hasn't been detected yet. Of course, it may be the other way around...but rolling twice isn't quite the same as rolling once against a higher number. It involves some complicated math I can't currently remember to figure out the actual detection percentage if the check is made this way, but it won't be a straight 15%. Arrow Quivershaft 16:30, 8 March 2008 (PST)
Actually, the engine checks first if the ship is in range of a hyperwave device (raw range of 800) and stop the checks if so. If not, it checks if in range of a large radar (distance 750) and if so, saves the long range capacity of the base (offset 0x12 in BASE.DAT). Then it checks if in range of small radar (500) and if so, saves the small range detection of the base (offset 0x10 in BASE.DAT), overwriting the value of long range detection. Finally, it throws dices. From the way it looks, if it is possible to have 0 small range detection capability and >0 long range capability, then it'll be impossible to detect a UFO in small range because it'll use the small range capability value (can anyone check this?). Seb76 17:32, 8 March 2008 (PST)
And the short range detection percentage definitely is additive, 20 + 10, this can be seen from the BASE.DAT files. It probably should be multiplied together (like in the algorithm above) instead of added, but there you go. It's added and that's that.
It would make it a lot easier to do the multiple radar algorithm if the combination wasn't additive. Then short range detection for multiple radars would be a simple function f(S,L). Instead I think it's inexpressible as a single function. With the simple function, short range detection for 1 SR, 1 LR would be 28% instead of 30%. So if I ever get round to implementing this I may live with that as an approximation, to save myself the coding headache. Spike 17:18, 9 March 2008 (PDT)

Implementation!

OK it's now implemented as part of this utility: BaseFixer. I used a simplified algorithm which is just the product of the effectiveness of all the radars, calculated for each band (short or long) in which that type radar is effective. There is a hard coded exception to force 1 Small, 1 Large to 30% Short, 20% Long (the formula would give 28% Short, 20% Long - didn't want any complaints!).

As mentioned above I decided not to worry too much about immediate updates. The utility can work with XcomUtil to update the MISSDAT files after each tactical mission, or it can be invoked manually to update any/all saved games files and/or MISSDAT.

I have yet to start my first game of UFO using this multiple radar capability. I can see a few situations where it might be used. Buying a pair or more small radars is a way of getting up and running faster in a new base (12 day build time), if you have money to burn. For the large radars, in most cases it's going to be more cost effective to put an extra large radar (if you can afford one), into a whole new base. By the time you've got 8 bases, in most games you would have Hyperwave decoders. It might be worth putting 2 Large Radars into your main, HQ base, to get better warning of attacks and scouts (assuming you care!), and maybe to pick up a few more intercepts if the aliens are busy in an area. It could work well with the 'one base' and 'one base - Hawaii' scenarios. At least until you start running out of base slots.

The strategy would work best in combination with the 'upgrade in place' bug/feature. As luck would have it the way I wrote the utility, you specify separately which bugs you want to fix. So you can leave 'upgrade in place' as a feature, while gaining extra detection for multiple radars. Of course the phantom small radar goes out of service the day the upgraded large radar comes online - fair enough!

It's a shame to have written the utility in Python, but it was fun to learn and also quick. In theory I should have done it as an XcomUtil add-on using SDUMP and the config files, but honestly the documentation was as scanty as it was impenetrable. I shall leave that as an exercise for someone brainier than me!

Spike 12:18, 24 March 2008 (PDT)

Radar ping overlaps?

My answer is probably already mentioned somewhere, but tl;dr and all that. Of the three detection types, are the radar checks done independently? That is, with a large radar, will it do two 20% checks for any UFOs when they are within the short range radius considering the long range radius also overlaps it? And if you had all three radar types in your base, would that mean three checks are done in the short range and two in the long range? I know that last one is a bit redundant considering the HDW's 100% rate, but still wondering if the checks are made. NKF (talk) 18:04, 3 January 2014 (EST)

Ranges info is so wrong

1. XCOM uses simple 3d distance formula for distances, with 2048 as maximum distance (sphere diameter).

2. All ingame distances are presented in this XCOM units

  • xcom craft = 200
  • small radar = 500
  • large radar = 750
  • hyperwave = 800
  • alien craft (for the retaliation) = 80

Obviously these values can't be converted into miles or kilometers with simple multiplication.

php script for conversion:

 $lenis=$_GET['val'];
 $radius=1024;
 $nm=1.85230925926;
 $earthradius=6367.7701745135;
 $result=asin($lenis/(2*$radius))*2*$earthradius;
 echo 'earth radius = '.$earthradius.'km; ';
 echo '1nm = '.$nm.'km; ';
 echo $lenis.' xcom units (3d distance) => (geodesic) '.$result.'km = '.$result/$nm.'nm  => '.$result/$earthradius;

With this script applied actual values are:

  • xcom craft = 672.50673939412nm
  • small radar = 1695.7263642837nm
  • large radar = 2577.8549855921nm
  • hyperwave = 2759.2073177146nm
  • alien craft (for the retaliation) = 268.64231530099nm

--Volutar (talk) 08:01, 15 July 2014 (EDT)