local function summon(id)

  local GPS = require('gps')
  local Socket = require('socket')
  local Point = require('point')

  turtle.status = 'GPSing'
  turtle.setPoint({ x = 0, y = 0, z = 0, heading = 0 })

  local pts = {
    [ 1 ] = { x = 0, z = 0, y = 0 },
    [ 2 ] = { x = 4, z = 0, y = 0 },
    [ 3 ] = { x = 2, z = -2, y = 2 },
    [ 4 ] = { x = 2, z = 2, y = 2 },
  }
  local tFixes = { }

  local socket = Socket.connect(id, 161)

  if not socket then
    error('turtle: Unable to connect to ' .. id)
  end

  local function getDistance()
    socket:write({ type = 'ping' })
    local _, d = socket:read(5)
    return d
  end

  local function doGPS()
    tFixes = { }
    for i = 1, 4 do
      if not turtle.gotoPoint(pts[i]) then
        error('turtle: Unable to perform GPS maneuver')
      end
      local distance = getDistance()
      if not distance then
        error('turtle: No response from ' .. id)
      end
      table.insert(tFixes, {
        position = vector.new(turtle.point.x, turtle.point.y, turtle.point.z),
        distance = distance
      })
    end
    return true
  end

  if not doGPS() then
    turtle.turnAround()
    turtle.setPoint({ x = 0, y = 0, z = 0, heading = 0})
    if not doGPS() then
      socket:close()
      return false
    end
  end

  socket:close()

  local pos = GPS.trilaterate(tFixes)

  if pos then
    local pt = { x = pos.x, y = pos.y, z = pos.z }
    local _, h = Point.calculateMoves(turtle.getPoint(), pt)
    local hi = turtle.getHeadingInfo(h)
    turtle.status = 'recalling'
    turtle.pathfind({ x = pt.x - hi.xd, z = pt.z - hi.zd, y = pt.y - hi.yd, heading = h })
  else
    error("turtle: Could not determine position")
  end
end

turtle.run(function() summon({COMPUTER_ID}) end)