Add decode_gps.py experiment

2 files changed, 27 insertions, 1 deletions

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))
diff --git a/python/igate.py b/python/igate.py
index 91edbcc..7c2e131 100755
--- a/python/igate.py
+++ b/python/igate.py
@@ -26,6 +26,9 @@ APRS_IS_SERVER = "france.aprs2.net"
 APRS_IS_PORT = 8080
 CALLSIGN = "HB9EGM-10"
 
+# See https://github.com/aprsorg/aprs-deviceid/blob/main/ALLOCATING.md
+APRS_DEVICEID = "APZEGM"
+
 # 46°23.07' N 6°13.28'
 LATITUDE = "4623.07N"
 LONGITUDE = "00613.28E"
@@ -132,7 +135,7 @@ try:
 
         if last_beacon_time + 1800 < now:
             last_beacon_time = now
-            packet = f"{CALLSIGN}>APLRG1,qAC:={LATITUDE}L{LONGITUDE}&{COMMENT}"
+            packet = f"{CALLSIGN}>{APRS_DEVICEID},qAC:={LATITUDE}L{LONGITUDE}&{COMMENT}"
             try:
                 send_frame_to_aprs_is(packet.encode())
             except Exception as ex: