From fb795285ca99d2c7d66a0771b4859e1fa5967da1 Mon Sep 17 00:00:00 2001
From: "Matthias P. Braendli" <matthias.braendli@mpb.li>
Date: Mon, 24 Jul 2023 14:16:33 +0200
Subject: Add decode_gps.py experiment

---
 python/experiments/decode_gps.py | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)
 create mode 100755 python/experiments/decode_gps.py

(limited to 'python/experiments')

diff --git a/python/experiments/decode_gps.py b/python/experiments/decode_gps.py
new file mode 100755
index 0000000..da7904a
--- /dev/null
+++ b/python/experiments/decode_gps.py
@@ -0,0 +1,23 @@
+#!/usr/bin/env python
+import struct
+from math import pow
+
+EXAMPLE_MSG = b"<\xff\x01HB9EGM-7>APLRT1,WIDE1-1:!/7%=6P\')8[I#Q"
+
+def decodeEncodedGPS(packet):
+    """Returns a string with decoded latitude and longitude, or raises ValueError"""
+    ix = packet.index(b":!/")
+    gps_packet = packet[ix+3:]
+    encoded_latitude = gps_packet[:4]
+    encoded_longitude = gps_packet[4:8]
+
+    (y1, y2, y3, y4) = struct.unpack("<bbbb", encoded_latitude)
+
+    decodedLatitude = 90.0 - ((((y1-33) * pow(91,3)) + ((y2-33) * pow(91,2)) + ((y3-33) * 91) + y4-33) / 380926.0);
+
+    (x1, x2, x3, x4) = struct.unpack("<bbbb", encoded_longitude)
+
+    decodedLongitude = -180.0 + ((((x1-33) * pow(91,3)) + ((x2-33) * pow(91,2)) + ((x3-33) * 91) + x4-33) / 190463.0);
+    return f"{decodedLatitude}N / {decodedLongitude}E"
+
+print(decodeEncodedGPS(EXAMPLE_MSG))
-- 
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