[G] ZvT Perfect Spine placement vs 2rax Bunker

2rax: a strategy where Terran player makes 2 barracks to pump out a large number of marines early on to pressure his opponent or outright win if possible. In TvZ, 2rax has been around for a long time. Many Zerg tears have been shed, but Zerg players have steadily adapted to 2rax builds. Although there are different styles in holding 2rax, once a bunker goes up, which is not always preventable due to terrain / good Terran micro / randomness in SCV construction movement etc., a spine crawler is often needed to hold the pressure. More often than not, Zerg player is forced to make a spine crawler at a safer place close to mineral line where it doesn’t initially reach the bunker so that it doesn’t die to marine fire while morphing, and relocate it later on. There are 2 ways to relocate a spine crawler: 1. Relocate so that the spine crawler outranges marines inside the bunker 2. Intentionally relocate the spine crawler within bunker range so that it tanks damage for hatchery/zergling/drone when going all-out ATAAAAAAACK mode vs bunker contain. While the latter is useful from time to time especially when hatchery is in range of the bunker and dying, focus fire by decent Terran player negates damage tanking by the spine crawler. Therefore, the former is the ideal spine crawler relocation most of the time. This thread primarily talks about this outranging spine crawler placement, which I call “perfect,” while I call other placements “fail.”

I think it is already a common knowledge today that spine crawler outranges marines in a bunker. Bunker increases the range of the units inside by 1 , so marine = 5range + 1range = 6range, when spine crawler = 7range. Of course, there is nothing special about outranging situation itself. There are many other cases in SC2 where one outranges another like stalker vs marine for example. What makes spine crawler vs bunker outranging situation special is that both are structures. Structures can only be placed according to grids unlike units, which completely ignore grids. Bounded by grids, x-y coordinates of structures on a map can shift to either direction only by an integer and never by a decimal. That is to say, there are only so many different structure placements relative to each other between the two. Therefore, I experimented every possible relative placement to see when outranging happens and when it doesn’t.

Some of you might have found my previous grid / sim city related guide [G] Zerg Sim City for Spire protection in ZvP useful. However, I must warn everyone here that this spine crawler vs bunker thread talks about interesting yet insanely specific topic that matters only on rare occasions. Welcome to the most extensive research on the most trifling topic in the history of SC2!!

Usually, only 1 spine crawler is made when facing 2rax, but Nestea made 2 spine crawlers in this game. 1st spine crawler relocation at the bottom is what I call perfect placement. 2nd spine crawler relocation at the top is what I call fail placement. The spine crawler at the bottom outranged the bunker. On the other hand, the spine crawler at the top was taking damage while rooting. In this particular game, 2nd spine crawler did a good job at tanking damage to save the hatchery, so it is not a complete fail, but for the sake of discussion, taking damage by rooting too close = fail in this thread. More analysis later in this thread after learning more about the topic.

I assume people know at least some basic math.

Unlike BW, SC2 structures are perfectly symmetrical.(thank god buildings in SC2 “make sense”) Therefore, the graph of 45 degrees above is all anyone needs to find out the relationship between the two structures because reflection/rotation of the results within 0-45 degrees explain the rest of 315 degrees as well. Reflection across the diagonal line gives 45-90 degrees, and rotation around the center of the bunker by 90 degrees gives 90-135 degrees etc. That is, every single perfect spine crawler placement in 360 degrees can be categorized into one of these 8 green diamonds. I hope the image is self-explanatory enough. Red is bunker. Green diamond is the center of perfectly placed spine crawler (2X2 structure). The corner of the bunker is taken as the original point for x-y coordinates (yellow point). Light green merely means that such a point appears every 90 degrees instead of every 45 degrees for other 7 darker greens. 360/45 = 8 and 360/90 = 4, so total number of perfect placements is 7*8+1*4 = 60 as can be seen in the 360 degrees image. Obviously, there is no way all 60 of them are available in 2rax situation, but usually at least around 5 locations are available on creep from which Zerg player only has to pick 1 when relocating. Any location inside is too close so that marines in the bunker can fire back while rooting. Any location outside is too far so that the spine crawler cannot attack the bunker.

[(7,-1) 270-315]


[(7,0) 270-315]


[(7,1) 270-315]


[(7,2) 270-315]


[(6,3) 270-315]


[(6,4) 270-315]


[(5,4) 270-315]


[(5,5) 270-360]


[(5,4) 315-360]


[(6,4) 315-360]


[(6,3) 315-360]


[(7,2) 315-360]


[(7,1) 315-360]


[(7,0) 315-360]


[(7,-1) 315-360]

[(7,-1) 0-45]


[(7,0) 0-45]


[(7,1) 0-45]


[(7,2) 0-45]


[(6,3) 0-45]


[(6,4) 0-45]


[(5,4) 0-45]


[(5,5) 0-90]


[(5,4) 45-90]


[(6,4) 45-90]


[(6,3) 45-90]


[(7,2) 45-90]


[(7,1) 45-90]


[(7,0) 45-90]


[(7,-1) 45-90]

Naming rule:
There are eight (6,4) placements in total because there is one every 45 degrees. [(6,4) 270-315] shows the (6,4) within 270-315 degrees. Same rule applies to other placements except for (5,5)
There are four (5,5) placements in total because there is one every 90 degrees, not 45 degrees. [(5,5) 270-360] shows the (5,5) within 270-360 degrees.

Unfortunately, white triangle dots that show the range of spine crawler are not spaced so that they are symmetrical. For whatever reason, there are 21 dots at 17.14degrees apart. This complicates distance estimation because [(6,4) 45-90] looks totally different from [(6,4) 180-225] in terms of graphical relationship between bunker and the closest white dots. Bunker's graphics can come right in between 2 dots like [(6,4) 45-90] only at certain angles, and therefore imaginary circle in your head has to be fairly accurate. Had Blizzard used 24 dots with exactly 15degrees apart, things would have been so much easier due to symmetry that would come with it.

As a general rule of thumb, imaginary circle connecting outer tips of the triangles must intersect with bunker’s graphics in order for the spine crawler to hit the bunker. In my experience, this is almost always true regardless of the camera angle. It is easier to imagine a circle with inner bases of the triangles, but using the tips seems more useful when estimating distance. Another useful rule to remember is that 0-180 spine crawlers look closer than 180-360 equivalents, especially between 45-135 and 225-315. Compare [(7,-1) 45-90] and [(7,-1) 270-315] to see the difference. (first image and last image) It is really hard to come up with any better universal rules in words due to factors like camera angle, asymmetry of bunker’s graphics for top and bottom half, discontinuous range indicator etc.

[(6,-1) 0-45]


[(6,0) 0-45]


[(6,1) 0-45]


[(6,2) 0-45]


[(5,3) 0-45]


[(4,4) 0-90]

[(8,-1) 0-45]


[(8,0) 0-45]


[(8,1) 0-45]


[(8,2) 0-45]


[(7,3) 0-45]


[(7,4) 0-45]


[(6,5) 0-45]

Do you think they are too obvious? (4,4) every 90 degrees and others fails every 45 degrees means that 12*8+1*4 = 100 fail placements in total. 60 perfect + 100 fail =160 relevant x-y coordinates in total. Some perfect ones look like fail, and some fail ones look like perfect because of camera angle etc. Telling the difference with 100% confidence is possible with dedicated practice, but it takes at least several hours of messing around with unit tester.

[(5,4) 0-45]


[(5,4) 45-90]


[(5,4) 90-135]


[(5,4) 135-180]


[(5,4) 180-225]


[(5,4) 225-270]


[(5,4) 270-315]


[(5,4) 315-360]

[(7,3) 0-45]


[(7,3) 45-90]


[(7,3) 90-135]


[(7,3) 135-180]


[(7,3) 180-225]


[(7,3) 225-270]


[(7,3) 270-315]


[(7,3) 270-315-360]

First spine crawler at the bottom was morphed at [(7,4) 180-225] which was too far to reach the bunker. Nestea relocated it to the right by 1 grid = [(6,4) 180-225]. Because hatchery and ramp limited rootable locations, the only other perfect placements available were [(5,4) 180-225] and [(5,5) 180-270] for Nestea. Although morphing spine crawler at [(6,4) 180-225] would have saved Nestea about 15sec for relocation, creep was not available at that point, so relocation was needed anyways.
Nestea relocated second spine crawler to [(6,2) 180-225] relative to the second bunker. (6,2) is one of the close fail placements as explained in this thread. [(7,2) 180-225] and [(7,1) 180-225] perfect placements were available, so the spine crawler didn’t have to take damage while rooting. [(7,1) 135-180], [(7,2) 135-180] and [(6,3) 135-180] would have been available as well if creep had spread far enough. [(7,1) 225-270] etc. were in range of the other bunker, so it was not appropriate. For example, [(7,1) 225-270] relative to the second bunker = [(5,2) 180-225] relative to the first bunker. This is Orek's analysis desk.

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360 degrees


90 degrees


45 degrees


BUUUUUT once a marauder (= 6+1 =7 range) is out, this is entirely useless.

Well, I didn’t mean to go this deep when I started the research. After spending tons of hours into this research, it is safe to say that I have deeper understanding of spine crawler placement vs bunker than anyone else in the world as of writing. If GSL spine crawler placement competition were held, it would make me rich. I don’t really expect anyone to spend as much time as I did on this seemingly unimportant aspect of the game. However, if you are a full-time pro, it doesn’t hurt to spend a few hours with unit tester to get the hang of it while referencing this thread. Or, upon misplacing a spine crawler in your game, checking replay to see how you failed might be helpful in future so as not to repeat the same mistake. No one has reached the level of “that was (7,3) so I wasted about 15 seconds by having to relocate spine crawler twice. It should have been (7,2) or (6,3).” If one has to face a 2rax lover in Code S final, maybe that’s the level of analysis required by coach/teammates in practice. Anyways, thanks for reading to the end. Feedback/correction is much appreciated. Check other thorough researches of mine linked below which are far more useful than ultra trifling topic I chose for this thread. You won’t regret.