From ba95010ed09beeed003c06aeeffe2d0a571e4a30 Mon Sep 17 00:00:00 2001
From: Christopher Young <cyoung@gmail.com>
Date: Wed, 9 Sep 2015 16:31:36 -0400
Subject: [PATCH] Misc tools.

---
 test/extract_latlng.go | 75 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 75 insertions(+)
 create mode 100644 test/extract_latlng.go

diff --git a/test/extract_latlng.go b/test/extract_latlng.go
new file mode 100644
index 00000000..b85b135b
--- /dev/null
+++ b/test/extract_latlng.go
@@ -0,0 +1,75 @@
+package main
+
+import (
+	"bufio"
+	"encoding/hex"
+	"fmt"
+	"os"
+	"strings"
+)
+
+const (
+	UPLINK_FRAME_DATA_BYTES = 432
+)
+
+func decodeUplink(frame []byte) {
+	raw_lat := (uint32(frame[0]) << 15) | (uint32(frame[1]) << 7) | (uint32(frame[2]) >> 1)
+
+	raw_lon := ((uint32(frame[2]) & 0x01) << 23) | (uint32(frame[3]) << 15) | (uint32(frame[4]) << 7) | (uint32(frame[5]) >> 1)
+	lat := float64(raw_lat) * 360.0 / 16777216.0
+	lon := float64(raw_lon) * 360.0 / 16777216.0
+
+	if lat > 90 {
+		lat = lat - 180
+	}
+	if lon > 180 {
+		lon = lon - 360
+	}
+	
+	fmt.Printf("%.04f, %.04f\n", lat, lon)
+
+}
+
+func parseInput(buf string) {
+	buf = strings.Trim(buf, "\r\n") // Remove newlines.
+	x := strings.Split(buf, ";")    // We want to discard everything before the first ';'.
+	if len(x) == 0 {
+		return
+	}
+	s := x[0]
+	if len(s) == 0 {
+		return
+	}
+	if s[0] != '+' {
+		return // Only want + ("Uplink") messages currently. - (Downlink) or messages that start with other are discarded.
+	}
+
+	s = s[1:]
+
+	if len(s)%2 != 0 { // Bad format.
+		return
+	}
+
+	if len(s)/2 != UPLINK_FRAME_DATA_BYTES {
+		fmt.Printf("UPLINK_FRAME_DATA_BYTES=%d, len(s)=%d\n", UPLINK_FRAME_DATA_BYTES, len(s))
+		panic("Error")
+	}
+
+	// Now, begin converting the string into a byte array.
+	frame := make([]byte, UPLINK_FRAME_DATA_BYTES)
+	hex.Decode(frame, []byte(s))
+
+	// Decode the frame.
+	decodeUplink(frame)
+}
+
+func main() {
+	reader := bufio.NewReader(os.Stdin)
+	for {
+		buf, err := reader.ReadString('\n')
+		if err != nil {
+			break
+		}
+		parseInput(buf)
+	}
+}