My brother tells me that to some extent, Minecraft has become a tradition for a lot of WoW players during Tuesday night maintenance. I had been going to post an ArkInventory tutorial here tonight, but since WoW is down, I thought I'd go with this instead; it's an article repost that I wrote on the Minecraft forums late last year, on how to get Nether portals working. This seems to be something which a lot of people find difficult, so hopefully this information will help someone.
The thread also contains a link to a YouTube video, added just tonight, from a user who was able to use not only my post, but also the research of a user named Addicted, to get his portals working.
I'm aware that there are possibly a few people who are still having difficulty with getting their Nether portals working. This was originally sent in a private message to someone who PMed me in response to an earlier offer I made last month, to help fix people's portals; but I figured that there are probably a number of other people who could still benefit from it as well, so I decided to also post it here.
One area where I'm a fairly incurable science fiction geek, is physics relating to teleportation or other unconventional means of transportation. That's meant Stargate, and it's also meant Sliders as well. So for me, the Nether portal has been the single most exciting addition that Notch has made to the game; I love these things. For a while, however, they frustrated the hell out of me. I had to satiate my hunger for the ability to do this (http://www.youtube.com/watch?v=8HWyAODVsQ4) within Minecraft, however, and so eventually I sat down and over a period of 12 solid hours of experimentation and tearing my hair out, assisted by this thread (viewtopic.php?f=35&t=93046) from Addicted, and the awesome contributions of uecasm and Mr. B, this is what I eventually figured out.
The portals (and Minecraft's geography in general) work via a Cartesian coordinate system. There are numbers on three axes; x, y, and z. Y represents elevation; the other two are length and width. The Nether and the surface world each use their own numerical grid; however both start from zero.
The Nether has a space compression co-efficient of 8, relative to the surface world, on both the x and z axes. What this means in English is that for every horizontal block of distance you walk in the Nether, by doing so you will have traveled the equivalent of 8 blocks in the surface world.
Another way to express this, would be to imagine a horizontal 10 centimeter line, drawn on a piece of paper, with a 2 centimeter line below it. The 10 centimeter line represents the surface world, and the 2 centimeter line represents the Nether. Because the 2 cm line is so much shorter, it can't contain references for literally all of the 10 cm, but by linking with the part of the 2 cm line that in scale represents the 6 cm point on the 10 cm line, you can get bounced back to that point on the 10 cm line, without having to move the whole 6 cm.
As an example, the Nether portal in my gateroom has coordinates of 9, 48, 308. What that means is that the portal is 48 blocks in height, distant from the 0 block, (the last layer of bedrock) 9 blocks distant from the 0 block in length or width, and 308 blocks from zero on the other axis. I usually have to try and remind myself what each one is every time, aside from elevation, as I don't always remember.
So if I have built a portal at that location in the surface world, if I want to find out the exact location that a corresponding portal should be built in the Nether, I divide both the first and third numbers by 8. I do not divide the second number, because elevation is the same in the Nether as the surface world; 132 blocks, from the last layer of bedrock, to the top of the sky.
So once I've divided those two numbers by 8, I go into the Nether. Now, if there is no other gate in the Nether at that time, there is a form of artificial intelligence in the game, which will try to automatically place the gate in the correct position for me. However, 45% of the terrain in the Nether is unsuitable for gates; it is either in midair, or in lava, or buried in hellstone. So if there is lava or hellstone in the way, or if there is no surface for the gate to be built on, the game will look for a close possible location instead, and build a gate there.
Initially, you will have no way of knowing this. So you will go back through the gate into the surface world, expecting to land back in your surface world gate room. However, the reason why you don't, is because the Nether portal (portal B) was at the wrong linking location for portal A, (the gateroom portal) and so portal B is *now* trying to guess the ideal location of *its'* matching portal in the *surface world.*
It is this guessing which the game does, that is the source of the problem. In order to solve it, you must place your portals manually, and destroy gates which are automatically placed by the game, which do not match the correct coordinates.
So taking the 3 numbers divided from our example, would give us 1, 48, 38. If instead you were at coordinates 1, 48, 38 in the Nether, and wanted to build a gate there, and know the right location for its' surface world partner, you would multiply both 1 and 38 by 8, to give you the coords 8, 48, 308 again.
We then use something like the SignTags mod, or the MinecraftGPS mod, which will allow us to view the coordinate location of the map that we are standing on, and doing that, we walk to coordinate location 1, 48, 38 in the Nether. When we get there, we will place the second obsidian block of the 4 block wide base of our gate, at those exact coordinates, with the first, third, and fourth blocks placed next to it.
Most of the time when we get there, we will find something in the way, which prevented the game from automatically placing our gate in the right location. This can be either lava, a hellstone mountain, or empty space, as mentioned. You will then have to build a scaffolding and a walkway up to the exact location of those coordinates, in order to place your gate. This can sometimes be very labour intensive if your gates are in midair, and for that reason I use Fly mod to allow me to build whatever staircases and walkways I need to, for connecting gates in the Nether, rather than having to initially build dangerous scaffolding and risk falling repeatedly into lava, etc, before my walkway is built. Fly mod also lets me fly up to the ceiling of the Nether and bucket a lava flow, rather than having to redirect it closer to the base.
You also must make a note of which way the surface world gate is facing, and make sure you build your gate to face in the same direction (whether North-South, or East-West) as well. If you enter a gate in the surface world, and come out staring at one side of the frame in the Nether, then even if the second obsidian block was correctly placed at the right coordinates, you will still need to rebuild the rest of the gate in order to face the right way.
This may seem obsessive, but if you place your gates manually, with this degree of precision, you will find that they work flawlessly, every time, and you will even be able to do such things as having multiple gates in the same chunk. I have three gates within the same 16 block Nether chunk (corresponding with 128 blocks in the surface world) and they all work perfectly.
I had exactly the same problem that most people have, for a month after the Halloween update, in terms of the same Nether portals all linking to the same one in the surface world. It is because of the distance difference. A Nether chunk is 16 blocks in the Nether, but that corresponds to 128 blocks in the surface world. The guessing AI is good enough that if you get two of the coordinates right, it can still work around the third one being wrong; but it can't guess for all three, and if all three of your gates are in the same Nether chunk, and at the wrong coordinates, it will get confused, and simply default to linking with the first surface world gate that was made.
There is one other trick that you can use, although I would not recommend trying to use this until you have got all of your gates working, using the exact elevation coordinates.
The trick is this; because the gates require coordinates on all three axes, then as long as you get two of the numbers exactly right, the guessing which the game does for the elevation axis (the second number) will usually still allow it to work. So, for example, you can build a gate at level 5 (the first level of bedrock) in the surface world, and as long as the coordinates for width and length were perfect in the Nether, you could place it directly next to a Nether gate which took you back to sea level in the surface world, without having to dig down to level 5 to place the gate in the Nether.
I am confident that if people are able to understand this, and get your portals working, that even though they can be initially much more labour intensive, you will find them a vastly superior form of transportation to minecarts. Minecarts work by increasing the speed of movement over the same surface area. Nether portals, on the other hand, literally reduce the amount of surface area needing to be crossed, by 80%. As mentioned, although a minecart will get you from bedrock to sealevel faster than walking, a Nether portal will get you there almost instantly, because the elevation difference does not need to be travelled at all.