GPS ambiguous position fix

sys/modules/opus/gps.lua

@@ -1,3 +1,5 @@
+local Util = require('opus.util')
+
 local GPS = { }
 
 local device = _G.device
@@ -89,19 +91,17 @@ end
 -- end stock gps api
 
 function GPS.trilaterate(tFixes)
-	local pos1, pos2 = trilaterate(tFixes[1], tFixes[2], tFixes[3])
+	local attemps = 0
-
+	for tFixes in Util.permutation(tFixes) do
+		attemps = attemps + 1
+		local pos1, pos2 = trilaterate(tFixes[4], tFixes[3], tFixes[2])
 		if pos2 then
-		pos1, pos2 = narrow(pos1, pos2, tFixes[4])
+			pos1, pos2 = narrow(pos1, pos2, tFixes[1])
+		end
+		if not pos2 then
+			return pos1, attemps
 		end
-
-	if pos1 and pos2 then
-		print("Ambiguous position")
-		print("Could be "..pos1.x..","..pos1.y..","..pos1.z.." or "..pos2.x..","..pos2.y..","..pos2.z )
-		return
 	end
-
-	return pos1
 end
 
 return GPS

sys/modules/opus/util.lua

@@ -799,4 +799,25 @@ function Util.getOptions(options, args, ignoreInvalid)
 	return true, Util.size(rawOptions)
 end
 
+-- https://www.lua.org/pil/9.3.html
+function Util.permutation(tbl)
+	local function permgen(a, n)
+		if n == 0 then
+			coroutine.yield(a)
+		else
+			for i=1,n do
+				a[n], a[i] = a[i], a[n]
+				permgen(a, n - 1)
+				a[n], a[i] = a[i], a[n]
+			end
+		end
+	end
+
+	local co = coroutine.create(function() permgen(tbl, #tbl) end)
+	return function()
+		local _, res = coroutine.resume(co)
+		return res
+	end
+end
+
 return Util