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It's known that traveling one block in the Nether is equivalent to traveling 8 blocks in the real world, and I can confirm that along the X and Z axes by building four portals: two in the Nether and two in the real world.

But I can't seem to corroborate the length dilation from the Nether to the real world along the Y axis (height).

That is, if I build the following portals:

  • Nether:
    • Portal 1 at n height
    • Portal 2 at n - 8 height
  • Real world:
    • Portal 3 at m height
    • Portal 4 at m - 64 height

I expect Portal 1 and 3 to link up while portal 2 and 4 should link up. But in my testing, if I use portal 1 or 2, they lead to portal 3, and if I use portal 3 or 4, they lead to portal 2.

Is there any evidence—in the form of a video, a world save file, or notch—that one nether block equals 8 real world blocks along the Y axis? I'm trying to determine if my error is in calculation or if it's in execution.


    Y     
    │      
    │      XYZ reference system
    └───X  for this question.
   ╱
  ╱ 
 Z
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8  
@Arda it's the coordinate system Minecraft uses. –  user3389 Dec 18 '10 at 18:45
11  
@Arda: Alpha Level Format, Chunk File Format, NBT File Format. People familiar with the issue know that Y = height, it's explained in the question itself, and it's tangential to the question so I don't see why this is an issue. –  user3389 Dec 18 '10 at 19:06
1  
@Mark It is a tad hard to answer the question "Does length dilation affect the Y axis in the Nether?" when you're assuming that Z is elevation. It was just confusing. It wasn't explained in the question until @badp edited it (ie. when I placed my comment) –  user56 Dec 18 '10 at 19:42
3  
@Arda it was explained in the question before badp added the diagram (of which I'm appreciative nonetheless): "along the Y axis (height)". Stack Exchange is for questions to be answered by experts, right? A Minecraft expert is not and would not be confused by the coordinate system used in the question: it's pretty standard knowledge for those delving into the mechanics of the engine. –  user3389 Dec 18 '10 at 19:52
7  
@Arda Why would a Minecraft player who does not have technical knowledge of the engine answer a question that's about technical knowledge of the engine? –  user3389 Dec 18 '10 at 19:54

3 Answers 3

up vote 11 down vote accepted

According to this thread in the Minecraft Forums that seems to have peeked into the code, length dilation does not affect the y-axis.

http://www.minecraftforum.net/topic/345806-nether-portal-science/

Summary version

  • Calculate coordinate of destination based on entry coordinate. (X, Y, Z) <---> (X*8, Y, Z*8)

  • At destination, look for the closest active nether portal within a 128 block radius of the player (257x257x128 area centered on destination) (the Euclidean distance (the 3D distance)). Teleport player there if one exists.

  • If no portal exists in the 128 block radius, the game creates one by looking for the closest possible nearby position within a 16 radius column (33x33x128 area) that has enough space to spawn a portal. And teleports the player there.

  • And if there's no possible spawn position with solid ground, it just creates a portal at the destination anyway, converting any blocks in the way into a portal.

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According to the wiki:

If you place two portals on top of one another you will come out of the bottom one on the overworld and the top one in The Nether.

I read somewhere (I'm afraid I can't remember where) that a portal will always(?) connect to the nearest portal in the other world. Thus, the Overworld portals should connect to the nearest/highest Nether portal and the Nether portals should connect to the nearest/lowest Overworld portals.

This theory agrees with the wiki and with your received behavior.

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I don't think it'll work that way. I built a portal several blocks above two of my other portals in the nether, yet when I stepped through, I was about 2 dozen meters below sea level. My other portals were several meters above sea level. I don't know what the exact formula is for placing the portals, but I can tell you that nether portals won't necessarily link to the expected portal in the real world if there is more than one in a given area.

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I'm a little confused by what you're saying, but as I said in my question, I can confirm the functionality along the horizontal plane. –  user3389 Dec 18 '10 at 18:48
    
I have a portal in the nether that is at the highest elevation among my portals, but it leads to the portal that is at the lowest elevation in the real world (below sea level). Elevation is secondary to the chunk that the portal will be placed at. –  MBraedley Dec 19 '10 at 22:31

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