Turtle GPS self-tracker expansion (tutorial)

This tutorial will teach you how to make a Turtle more efficient in keeping track of its location when using the GPS API. This is essentially an API that uses the native Turtle movement API while using its own movement as a sensor to keep track of its location, so it only requires a GPS signal once, until it is turned off. This API requires every Turtle you want to use the API with to have it installed. I recommend using an Advanced Computer to write it on, move it to a Disk with a disk drive and moving it to the Turtle. Alternatively, if you are on Singleplayer or a Multiplayer admin and have access to the mod file, you can move it into the turtle/rom folder to have it automatically installed on every new turtle that is placed.

Important: When starting, the program assumes that it is facing west, so first you must face West and then place the turtle. Here are some ways to check where you are facing: You can see the sun/moon rising right in front of you. You are facing East. You can see the sun/moon falling right in front of you. You are facing West. Clouds go west. Check where they go. Press F3 and locate the number behind "f". This one is below "x", "y" and "z". If this number is 0, you are facing North. If this number is 1, you are facing West. If this number is 2, you are facing South. If this number is 3, you are facing East.

Code

Note: This will only work on a Turtle. That said, even if it worked on a computer, it wouldnt have any practical use because a computer cant move.
Before you start, you must add this to the program that you want to use it with at the top line:

os.loadApi("tst")

This will allow the program to use the API. This tutorial assumes that you use the file name "tst" for the API, but if you like to you can change it. You must then also change every reference to "tst" in your program, including the line above. Write this in the computer/turtle:

-- Turtle Self-tracking System created by Latias1290.

local xPos, yPos, zPos = nil
face = 1
cal = false

function setLocation() -- get gps using other computers
 xPos, yPos, zPos = gps.locate()
 cal = true
end

function manSetLocation(number x, number y, number z) -- manually set location
 xPos = x
 yPos = y
 zPos = z
 cal = true
end

function getLocation() -- return the location
 if xPos != nil then
  return xPos, yPos, zPos
 elseif xPos == nil then
  return nil
 end
end

function turnLeft() -- turn left
 if face == 0 then
  face = 1
 elseif face == 1 then
  face = 2
 elseif face == 2 then
  face = 3
 elseif face == 3 then
  face = 0
 end
end

function turnRight() -- turn right
 if face == 0 then
  face = 3
 elseif face == 1 then
  face = 0
 elseif face == 2 then
  face = 1
 elseif face == 3 then
  face = 2
 end
end

function forward() -- go forward
 turtle.forward()
 if cal == true then
  if face == 0 then
   zPos = zPos - 1
  elseif face == 1 then
   xPos = xPos - 1
  elseif face == 2 then
   zPos = zPos + 1
  elseif face == 3 then
   xPos = xPos + 1
  end
 else
  print("Not Calibrated.")
 end
end

function back() -- go back
 turtle.back()
 if cal == true then
  if face == 0 then
   zPos = zPos + 1
  elseif face == 1 then
   xPos = xPos + 1
  elseif face == 2 then
   zPos = zPos - 1
  elseif face == 2 then
   xPos = xPos - 1
  end
 else
  print("Not Calibrated.")
 end
end

function up() -- go up
 turtle.up()
 if cal == true then
  yPos = yPos + 1
 else
  print("Not Calibrated.")
 end
end

function down() -- go down
 turtle.down()
 if cal == true then
  yPos = yPos - 1
 else
  print("Not Calibrated.")
 end
 
 function jump() -- perform a jump. useless? yup!
  turtle.up()
  turtle.down()
 end

How to Use

This might seem daunting at the first moment. But dont worry, I will walk you through it. Note that to use it properly, you must always put "tst." in front of it, or how you named it followed by a dot. So if I wanted to have my turtle go 1 block forward, I typed "tst.forward()". Note that if you do not do either tst.getLocation OR tst.setLocation(coords), the API will print "Not Calibrated." every time you use a command. This will not prevent you from using it, however.

setLocation

To use this, you will need at least 4 computers equipped with a Wireless Modem, and having it host a GPS. More info about that here and here.

manSetLocation

For this one you will need to know the location of your turtle. Any location will work, but the API loses its point if you use another coordinate set. A good way to obtain the coordinates is to open up the debug screen(press F3), stand on the turtle, write down the x, y and z fields, substract 1 from the Y coordinate and use these.

getLocation

This one is pretty simple. It returns the coordinates. Note that you will have to overwrite all of them. For example, if we had the variables x, y and z, and we wanted to have the value set to our location, we did this:

x, y, z = tst.getLocation()

Simple right? Note that this will return nil if you are not calibrated, which means if you do it before you do setLocation or manSetLocation, x, y and z will be null!

forward, back, up, down, turnLeft and turnRight

This one is pretty easy as well. It makes your turtle move 1 block in the direction you used(its obvious which function goes where) and update its location according to where it went.

jump

This one works a bit different. It makes the turtle go up, then go down. "But thats useless!" you might say, and indeed it is!