Added python parser for raw pico tracker data.

I haven't rigorously tested it, but the fact that the data starts in
Montpelier on the 25th, and it correctly decodes the APRS test longitude of
'<*e7' to -72.75 degrees is promising.

firmware/tools/raw_parser.py

@@ -0,0 +1,140 @@
+"""
+This script parses the raw data from the pico tracker.
+At the very bottom the data is printed. Feel free to change
+the print statement to suit the data you're interested in.
+The parsed data is a list of dicts, with keys 'time', 'coords',
+'battery', 'solar', 'temperature' and 'satellites'.
+
+Data is expected in the form of a series of lines containing
+'/A={6 digits} {6 digits}z.{18 chars}{11 chars}\n'. Anything
+else will be ignored.
+"""
+
+import re
+import sys
+from datetime import datetime
+from math import log, exp
+
+"""
+Decodes a 'base 91' encoded string
+"""
+def base91_decode(enc_str):
+    enc_ints = [ord(x) - 33 for x in enc_str]
+    powers = range(len(enc_ints))[::-1]
+    return sum(x * pow(91, i) for x, i in zip(enc_ints, powers))
+
+"""
+Takes a parsed telemetry line and returns a datetime
+Default year and month are 2015 and July
+"""
+def extract_time(line):
+    # Capture a 6 digit string
+    p = re.compile(r'(\d{6})z\S{18}')
+    match = p.match(line) 
+
+    if match == None:
+        return None
+    else:
+        date_str = '201507' + match.group(1)
+
+        # Return a datetime object
+        return datetime.strptime(date_str, '%Y%m%d%H%M')
+
+"""
+Takes a parsed telemetry line and returns latitude, longitude and
+altitude. It decodes from base 91 along the way
+"""
+def extract_lat_long_alt(line):
+    # Capture a 4 char encoded latitude
+    p = re.compile(r'\d{6}z(\S{4})(\S{4})(\S{2})\S{8}')
+    match = p.match(line)
+
+    if match == None:
+        return None
+    else:
+        enc_lat, enc_long, enc_alt = match.groups()
+
+        # Lat/long in fractional degrees, alt in metres
+        latitude =  90.0 - (base91_decode(enc_lat) / 380926.0)
+        longitude = -180.0 + (base91_decode(enc_long) / 190463.0)
+        altitude = exp(log(1.002) * base91_decode(enc_alt)) / 3.2808
+
+        return (latitude, longitude, altitude)
+
+"""
+Takes a parsed telemetry line and returns readings on battery, solar
+temperature and satellite count. It decodes from base91 along the
+way
+"""
+def extract_telemetry(line):
+    # Capture an 8 char encoded telemetry segment
+    p = re.compile(r'\d{6}z\S{10}(\S{8})')
+    match = p.match(line)
+
+    if match == None:
+        return None
+    else:
+        tel = match.group(1)
+
+        # Split into 2 char chunks
+        parts = [tel[i:i+2] for i in range(0, 8, 2)]
+        batt_enc, sol_enc, temp_enc, sat_enc = tuple(parts)
+
+        # Reverse Richard's conversions
+        battery = base91_decode(batt_enc) / 1000.0
+        solar   = base91_decode(sol_enc) / 1000.0
+        temperature = (base91_decode(temp_enc) / 10) - 273.2
+        satellite_count = base91_decode(sat_enc)
+
+        return (battery, solar, temperature, satellite_count)
+
+"""
+Exracts the 'raw data' segment from a line of data; this is the 25
+character section after /A={6 digits}
+"""
+def extract_raw_data(line):
+    # Capture the raw data segment
+    p = re.compile(r'/A=\d{6} (\S{25})\|\S{11}$')
+    match = p.search(line)
+
+    if match == None:
+        return None
+    else:
+        return match.group(1)
+
+#-------------------------------------------------------------------------------
+
+if len(sys.argv) != 2:
+    print 'Usage: python raw_parser.py rawdata.txt'
+    sys.exit()
+
+file_name = sys.argv[1]
+
+with open(file_name, 'r') as data_file:
+    data = []
+
+    for line in data_file:
+        # Extract raw data string
+        raw = extract_raw_data(line)
+
+        if raw == None:
+            continue
+        else:
+            tele = extract_telemetry(raw)
+
+            data.append({
+                'time': extract_time(raw),
+                'coords': extract_lat_long_alt(raw),
+                'battery': tele[0],
+                'solar': tele[1],
+                'temperature': tele[2],
+                'satellites': tele[3]
+            })
+
+    # Sort data lines by time
+    data = sorted(data, key=lambda x: x['time'])
+
+    # Print data
+    for datum in data:
+        print "%s: %s, %s" % ((str(datum['time']),) + datum['coords'][:2])
+