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94 lines
5.5 KiB
Markdown
94 lines
5.5 KiB
Markdown
---
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module: [kind=guide] gps_setup
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---
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<!--
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SPDX-FileCopyrightText: 2022 The CC: Tweaked Developers
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SPDX-License-Identifier: MPL-2.0
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-->
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# Setting up GPS
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The [`gps`] API allows computers and turtles to find their current position using wireless modems.
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In order to use GPS, you'll need to set up multiple *GPS hosts*. These are computers running the special `gps host`
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program, which tell other computers the host's position. Several hosts running together are known as a *GPS
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constellation*.
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In order to give the best results, a GPS constellation needs at least four computers. More than four GPS hosts per
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constellation is redundant, but it does not cause problems.
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## Building a GPS constellation
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<img alt="An example GPS constellation." src="/images/gps-constellation-example.png" class="big-image" />
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We are going to build our GPS constellation as shown in the image above. You will need 4 computers and either 4 wireless
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modems or 4 ender modems. Try not to mix ender and wireless modems together as you might get some odd behavior when your
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requesting computers are out of range.
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> [Ender modems vs wireless modems][!TIP]
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> Ender modems have a very large range, which makes them very useful for setting up GPS hosts. If you do this then you
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> will likely only need one GPS constellation for the whole dimension (such as the Overworld or Nether).
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>
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> If you do use wireless modems then you may find that you need multiple GPS constellations to cover your needs.
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>
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> A computer needs a wireless or ender modem and to be in range of a GPS constellation that is in the same dimension as
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> it to use the GPS API. The reason for this is that ComputerCraft mimics real-life GPS by making use of the distance
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> parameter of [modem messages][`modem_message`] and some maths.
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Locate where you want to place your GPS constellation. You will need an area at least 6 blocks high, 6 blocks wide, and
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6 blocks deep (6x6x6). If you are using wireless modems then you may want to build your constellation as high as you can
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because high altitude boosts modem message range and thus the radius that your constellation covers.
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The GPS constellation will only work when it is in a loaded chunk. If you want your constellation to always be
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accessible, you may want to permanently load the chunk using a vanilla or modded chunk loader. Make sure that your 6x6x6
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area fits in a single chunk to reduce the number of chunks that need to be kept loaded.
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Let's get started building the constellation! Place your first computer in one of the corners of your 6x6x6. Remember
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which computer this is as other computers need to be placed relative to it. Place the second computer 4 blocks above the
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first. Go back to your first computer and place your third computer 5 blocks in front of your first computer, leaving 4
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blocks of air between them. Finally for the fourth computer, go back to your first computer and place it 5 blocks right
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of your first computer, leaving 4 blocks of air between them.
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With all four computers placed within the 6x6x6, place one modem on top of each computer. You should have 4 modems and 4
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computers all within your 6x6x6 where each modem is attached to a computer and each computer has a modem.
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Currently your GPS constellation will not work, that's because each host is not aware that it's a GPS host. We will fix
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this in the next section.
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## Configuring the constellation
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Now that the structure of your constellation is built, we need to configure each host in it.
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Go back to the first computer that you placed and create a startup file, by running `edit startup`.
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Type the following code into the file:
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```lua
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shell.run("gps", "host", x, y, z)
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```
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Escape from the computer GUI and then press <kbd>F3</kbd> to open Minecraft's debug screen and then look at the computer
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(without opening the GUI). On the right of the screen about halfway down you should see an entry labeled `Targeted
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Block`, the numbers correspond to the position of the block that you are looking at. Replace `x` with the first number,
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`y` with the second number, and `z` with the third number.
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For example, if I had a computer at x = 59, y = 5, z = -150, then my <kbd>F3</kbd> debug screen entry would be `Target
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Block: 59, 5, -150` and I would change my startup file to this `shell.run("gps", "host", 59, 5, -150)`.
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To hide Minecraft's debug screen, press <kbd>F3</kbd> again.
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Create similar startup files for the other computers in your constellation, making sure to input the each computer's own
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coordinates.
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> [Modem messages come from the computer's position, not the modem's][!WARNING]
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> Wireless modems transmit from the block that they are attached to *not* the block space that they occupy, the
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> coordinates that you input into your GPS host should be the position of the computer and not the position of the modem.
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Congratulations, your constellation is now fully set up! You can test it by placing another computer close by, placing a
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wireless modem on it, and running the `gps locate` program (or calling the [`gps.locate`] function).
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> [Why use Minecraft's coordinates?][!INFO]
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> CC doesn't care if you use Minecraft's coordinate system, so long as all of the GPS hosts with overlapping ranges use
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> the same reference point (requesting computers will get confused if hosts have different reference points). However,
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> using MC's coordinate system does provide a nice standard to adopt server-wide. It also is consistent with how command
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> computers get their location, they use MC's command system to get their block which returns that in MC's coordinate
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> system.
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