From 9be1d36166eabdde60a16df23f3bff99d10e6cd0 Mon Sep 17 00:00:00 2001
From: cyberman54 <cyberman@obh.snafu.de>
Date: Sat, 27 Jul 2019 15:23:17 +0200
Subject: [PATCH] fixed TTN decoder for gps altitude

---
 src/TTN/packed_decoder.js | 8 +++++++-
 src/TTN/plain_decoder.js  | 6 +++++-
 2 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/src/TTN/packed_decoder.js b/src/TTN/packed_decoder.js
index 2c5752f8..66846cf7 100644
--- a/src/TTN/packed_decoder.js
+++ b/src/TTN/packed_decoder.js
@@ -151,7 +151,13 @@ var altitude = function (bytes) {
     if (bytes.length !== altitude.BYTES) {
         throw new Error('Altitude must have exactly 2 bytes');
     }
-    return +(bytesToInt(bytes) / 4 - 1000).toFixed(1);
+
+    var alt = bytesToInt(bytes);
+    if (alt > 32767) {
+        alt -= 65536;
+    }
+
+    return +(alt / 4 - 1000).toFixed(1);
 };
 altitude.BYTES = 2;
 
diff --git a/src/TTN/plain_decoder.js b/src/TTN/plain_decoder.js
index c6eba7b4..4158515a 100644
--- a/src/TTN/plain_decoder.js
+++ b/src/TTN/plain_decoder.js
@@ -41,7 +41,11 @@ function Decoder(bytes, port) {
     decoded.longitude = ((bytes[i++] << 24) | (bytes[i++] << 16) | (bytes[i++] << 8) | bytes[i++]);
     decoded.sats = bytes[i++];
     decoded.hdop = (bytes[i++] << 8) | (bytes[i++]);
-    decoded.altitude = ((bytes[i++] << 8) | (bytes[i++])) / 4 - 1000;
+    var alt = ((bytes[i++] << 8) | (bytes[i++]));
+    if (alt > 32767) {
+      alt -= 65536;
+    }
+    decoded.altitude = alt / 4 - 1000;
   }
 
   if (port === 5) {