EPT![[image loading]](http://www.teamliquid.net/staff/SilverskY/SCIIConceptBanner.jpg)
Don't get comfortable Aldaris. You're going to be chastising many a Protoss for not having enough gas for many years to come.
Don't let the extra geyser fool you. Things have changed in so far as concerns our favorite gaseous resource, vespane gas, and in quite a few far reaching and profound ways. And it's not just Aldaris who needs to be on his toes. Every race has been affected by the changes made to resource collection in general, not just vespane gas, and the consequences are large.
Although most will know this, here is a summary to the basic changes to gas collection:
- geysers now return only 4 gas a trip
- every main and expo in the map pool has 2 geysers
- geysers are 75 minerals (25 for zerg + the assumed 50 for the drone)
- geysers return no gas once depleted
So naturally this plays much differently in terms of teching, but with some interesting options. These changes make gas collection more graded, which in Brood War was accomplished by yanking miners off the geyser. That reduced the collection rate substantially, and it was only with real purpose that workers would be taken from gas.
Thus, in Brood War, gas, more or less throughout the game, had 2 gears: high or none. Yes, Terrans would pull SCVs in the opening but the majority of every match had 3 on gas once the mining structure was complete. But that's not so in SC2. There are debates about how heavily to invest in gas, when, and what the best combination is. To this end, I did a detailed analysis of gas collection rates with the 9 possible (read, reasonable) combinations of gas collection based on the number of geysers used (in parentheses) and the number of miners used.
Granted this analysis is limited in scope. While I strongly suspect there are no differences in gas collection rates between the races, my analysis was limited only to Terran, on Lost Temple at 6 o'clock. Of course, I am assuming that these are typical geyser positions and there are no differences between the gas collection rates between the races, and there were other moderate sources of error, namely a non-uniform starting place for the gas collection, but this is normed by the large number of data points and the absolute nature of gas collection. Thus, by linear regression, an approximation of the rate of gas collection can be ascertained, but more importantly, its relation to other methods of gas collection.
In the spoiler is the raw data table. If people want to analyze the replays from which I got these data, I can release those as well.
+ Show Spoiler +
![[image loading]](/staff/Arrian/gascollectiondata.png)
Below are the individual data points as they stack up. Some error in imperfect data collection is visible but the overall pattern is fairly stable, and the conclusions are both rather intuitive and fairly reasonable. As noted above, the number of geysers taken is in parentheses and the number of miners collecting gas is beside it.
![[image loading]](/staff/Arrian/happygraph.png)
A few things to note before going on to the conclusions:
- The rate gas collection from 3(1) and 4(1) are identical. 3 miners saturates 1 geyser completely for all intents and purposes. In Brood War the rate of gas collection of 4 vs 3 was approximately 4 more gas for every 200, so the difference between 3(1) and 4(1) has not significantly changed between Brood War and SC2.
- The number of data points is uneven for each, although each has an acceptable minimum from which to draw conclusions.
- In order to better standardize the collection rates, measurement began after the first gas trip was concluded, which is why every line begins above 0. All are at 4 excepting 5(2) where both miners completed their first trips at identical times to start at 8.
So, with that out of the way, it is generally true that the graph validates the intuitions of most players and many conclusions carry over from Brood War. Despite how obvious many of these may seem to be, it is important to note every one of them because SC2 is a different game, and the changes to resource collection have been substantial. So, taking nothing for granted, to make everything prettier and easier to read, I will once again bullet the conclusions:
- With the exception of 4(1) and 3(1), having more miners on gas increases the gas collection rate. You do not see the line for 3(1) because it perfectly overlaps with 4(1).
- There is no significant difference between 2 miners on separate geysers and having 2 miners on the same geyser (see the lines for 2(2) and 2(1)).
- Possibly the most interesting conclusion from the graph is the difference between 3(2) and 3(1). The collection rate of 3(2) is significantly faster than that of 3(1). This would seem to make sense; miners have a brief idle period in 3(1) that is not realized in 3(2), allowing for faster gas collection.
- There are clear 'don'ts' for gas collection as relates to mineral economy; 4(1), 2(2), and possibly 1(1) waste a disproportionate amount of time or minerals per gas gained.
Now is an appropriate time for an aside. I chose the Lost Temple 6 o'clock because it has a fairly typical mining distance, but not all geysers are created equal. Some, like those on Metalopolis, have very short distances and can run at much greater efficiency than those on Kulas Ravine, for example. In instances where the distances are shorter, the difference in the rate of collection between 3(1) and 3(2) is more exaggerated because there is a longer layover for the 3rd miner and because 2 miners is already very efficient, but on those where the distances to the gas are longer the difference is mitigated somewhat by the shorter layover.
The exact collection rates, however, are far more useful to draw conclusions from. SC2 replays give vague and imprecise collection rates under the 'income' tab which are hardly of any significant utility to a player trying to decide when to pull miners off gas, how many miners are needed, and when to start a second geyser, especially in-game. The following are the collection rates based on linear regressions from data of the chart above. The b values have all been dropped because they don't mean anything aside from the consequences of my norming, and remember that the m value (the rate) is in vespane gas/second, but since vespane gas isn't collected continuously but rather in chunks of 4 these rates are only useful in so far as they are compared to other rates of the same units and won't give you measures in seconds on when you can most closely time your Orbital Command, for example. That having been said, here they are:
- 1(1) | 0.74 gas/second
- 2(1) | 1.50 gas/second
- 2(2) | 1.48 gas/second
- 3(1) | 2.00 gas/second
- 3(2) | 2.23 gas/second
- 4(2) | 3.05 gas/second
- 5(2) | 3.33 gas/second
- 6(2) | 3.94 gas/second
Several things stand out from this. First, as could be expected, having 2 miners on the same gas doubles the collection rate, and having 2 miners on 2 separate gas does the same. However, noticeably, having 3 miners on the same gas does not triple the collection rate, but having 2 on 1 gas and 1 on the other does (because of the aforementioned brief traffic jam on a saturated geyser). Having 4 gas on 2 quadruples the collection rate, but again upon saturation of 1 the collection rate does not gain as much, and further unto the saturation of a second. Perhaps more useful here would be to look at a somewhat unusual comparison, but paradoxically far more comprehensible to your average player, being seconds/gas. Essentially, we're just flipping the previous collection rates on their heads to get something far more useful out of it. The following is how many seconds there are between gas returns.
- 1(1) | 5.40 seconds
- 2(1) | 2.66 seconds
- 2(2) | 2.70 seconds (*this is not a significant difference from 2(1))
- 3(1) | 2.00 seconds
- 3(2) | 1.79 seconds
- 4(2) | 1.31 seconds
- 5(2) | 1.20 seconds
- 6(2) | 1.00 seconds
Now, a very compelling pattern emerges here, one that looks like an exponential function. I took this and graphed it. Now, naturally, the actual data is more accurate than the function, and several manipulations removed from the actual data we're really getting into abstractions here, but the below graph essentially tells us that the amount of time exponentially decreases with each added miner per the function (calculated via exponential regression) f(x)=8.02477326e^-.4418030032x
![[image loading]](/staff/Arrian/gasexpfunction.png)
The graph bears some discussion. Naturally, the actual utility of the graph cuts off after 6, because geysers are saturated at 3. The fit also isn't perfect, especially because 3(2) is quite anomalous to the pattern and is also very difficult to precisely compensate for, but the graph does reflect the effect that adding additional miners has on the speed of gas returns.
What this means for actual play could be very significant, or not so much. Gas always seems to be in high demand, and its collection is far more limited than mineral collection, but the amount of options in adjusting collection rates and the varying methods of investment allow intriguing possibilites for opening timing windows or interesting transitions. Essentially, what the gas changes have meant to play thus far is that there no longer need be just two settings for a player's gas collection, that you can alter and adjust the rate of gas collection based on needs and especially transitions and openings. This graph shows the value of each miner relative to the next or the one before it, and perhaps can, with care, be used to calculate more precise timings and adjustments for gas needs.
With all of this information we can also calculate which early gas is most cost efficient per minerals invested. With this, we actually use the rate of gas collection because it's easier to think about (in my opinion). Below is a friendly table that will make everything prettier to look at.
![[image loading]](/staff/Arrian/efficiency_table.png)
Unfortunately the table is the organized more by the scrambled nature of my brain than any real organizing principle so things may not be immediately apparent. Some things, as with the other graphs and pretty pictures, should stand out immediately, though. Namely, the value of adding just one more miner to gas early is huge. For 40% of the initial investment, there is a 100% increase in returns. Also, there's hardly any reason to construct two early gas if only 2 miners will be dedicated to them. Most SC players know this of course, but I've seen it. The most interesting datum is the 3(1) v 3(2) contrast. For 75% of the investment, ~90% of the gas is returned. So, while 3(2) does mine significantly better than 3(1), it is probably not worth the investment. Some other conclusions may be gleaned, but this wouldn't be fun if I just told you everything, now would it?
The most important thing to remember is that this is an examination of a single race, on a single map, at a single starting position, in the beta test. Because also these data were largely meant to influence how the opening can play out and options for tech, I did not do any testing on the high yield geysers included in the map editor or any testing on the varying distances that the geysers are from the spawn location. While the conclusions from this examination can likely be extrapolated across many other situations, there is no guarantee that they can, and as much stock should be placed in this as it deserves.
And those are the gas matters.
EDIT: There seems to be a fair bit of confusion about the graph. Just so everyone is clear, I should have put a domain on it and cut it off after 6, or simply edited the image to go no further, but as it stands, my MSPaint skills are marginal at best. Of course, I never meant for the graph to mean anything before 1 or after 6, and some people were confused by this. I submit this as my correction.
This post was made by the Team Liquid Starcraft 2 Coverage Team. For more of TL's coverage, please visit the Team Liquid Starcraft 2 Beta Page.
