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-- startup.lua  (GPS node with hard-coded coords; CC:Tweaked)
-- Edit these:
local X, Y, Z = 100.0, 72.0, -340.0
 local function findWirelessModem()
  return peripheral.find("modem", function(_, p) return p.isWireless() end)
end
 term.clear(); term.setCursorPos(1,1)
print(("GPS node @ (%.3f, %.3f, %.3f)"):format(X,Y,Z))
 local modem = findWirelessModem()
if not modem then error("No wireless modem") end
local modemName = peripheral.getName(modem)
rednet.open(modemName)
 -- Try to advertise on the "gps" service (optional). Ignore errors if unavailable.
pcall(function() rednet.host("gps", "gps_"..os.getComputerID()) end)
 print("Wireless open on "..modemName..". Serving replies on protocol 'gps'.")
 -- Minimal GPS responder. Replies with {x=,y=,z=} to any 'gps' request.
while true do
  local senderId, msg, proto = rednet.receive("gps", 5)
  if senderId then
    rednet.send(senderId, { x = X, y = Y, z = Z }, "gps")
  end
  -- heartbeat
  term.setCursorPos(1,4)
  term.setTextColor(colors.lightGray)
  print("Last tick: "..textutils.formatTime(os.time(), true).."      ")
  term.setTextColor(colors.white)
end