From cc7ce36111bc0e5e7599c4cf8b3144fe55d1538b Mon Sep 17 00:00:00 2001
From: Junzi Sun <junzi.sun@gmail.com>
Date: Fri, 23 Oct 2015 14:01:20 +0200
Subject: [PATCH] fix major bug in latitude decoding

---
 decoder.py | 71 ++++++++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 69 insertions(+), 2 deletions(-)

diff --git a/decoder.py b/decoder.py
index 941d50f..b240277 100644
--- a/decoder.py
+++ b/decoder.py
@@ -156,7 +156,7 @@ def cpr2position(cprlat0, cprlat1, cprlon0, cprlon1, t0, t1):
     air_d_lat_odd = 360.0 / 59
 
     # compute latitude index 'j'
-    j = int(59 * cprlat_even - 60 * cprlat_odd + 0.5)
+    j = int(math.floor(59 * cprlat_even - 60 * cprlat_odd + 0.5))
 
     lat_even = float(air_d_lat_even * (j % 60 + cprlat_even))
     lat_odd = float(air_d_lat_odd * (j % 59 + cprlat_odd))
@@ -233,7 +233,7 @@ def get_callsign(msg):
     cs += chars[bin2int(csbin[42:48])]
 
     # clean string, remove spaces and marks, if any.
-    cs = cs.replace('_', '')
+    # cs = cs.replace('_', '')
     cs = cs.replace('#', '')
     return cs
 
@@ -253,3 +253,70 @@ def cprNL(lat):
     except:
         # happens when latitude is +/-90 degree
         return 1
+
+
+def cprNL_lookup(lat):
+    """
+    Lookup table to convert the latitude to index.
+    Slightly faster than calculation.
+    """
+    if lat < 0 : lat = -lat     # Table is simmetric about the equator.
+    if lat < 10.47047130 : return 59
+    if lat < 14.82817437 : return 58
+    if lat < 18.18626357 : return 57
+    if lat < 21.02939493 : return 56
+    if lat < 23.54504487 : return 55
+    if lat < 25.82924707 : return 54
+    if lat < 27.93898710 : return 53
+    if lat < 29.91135686 : return 52
+    if lat < 31.77209708 : return 51
+    if lat < 33.53993436 : return 50
+    if lat < 35.22899598 : return 49
+    if lat < 36.85025108 : return 48
+    if lat < 38.41241892 : return 47
+    if lat < 39.92256684 : return 46
+    if lat < 41.38651832 : return 45
+    if lat < 42.80914012 : return 44
+    if lat < 44.19454951 : return 43
+    if lat < 45.54626723 : return 42
+    if lat < 46.86733252 : return 41
+    if lat < 48.16039128 : return 40
+    if lat < 49.42776439 : return 39
+    if lat < 50.67150166 : return 38
+    if lat < 51.89342469 : return 37
+    if lat < 53.09516153 : return 36
+    if lat < 54.27817472 : return 35
+    if lat < 55.44378444 : return 34
+    if lat < 56.59318756 : return 33
+    if lat < 57.72747354 : return 32
+    if lat < 58.84763776 : return 31
+    if lat < 59.95459277 : return 30
+    if lat < 61.04917774 : return 29
+    if lat < 62.13216659 : return 28
+    if lat < 63.20427479 : return 27
+    if lat < 64.26616523 : return 26
+    if lat < 65.31845310 : return 25
+    if lat < 66.36171008 : return 24
+    if lat < 67.39646774 : return 23
+    if lat < 68.42322022 : return 22
+    if lat < 69.44242631 : return 21
+    if lat < 70.45451075 : return 20
+    if lat < 71.45986473 : return 19
+    if lat < 72.45884545 : return 18
+    if lat < 73.45177442 : return 17
+    if lat < 74.43893416 : return 16
+    if lat < 75.42056257 : return 15
+    if lat < 76.39684391 : return 14
+    if lat < 77.36789461 : return 13
+    if lat < 78.33374083 : return 12
+    if lat < 79.29428225 : return 11
+    if lat < 80.24923213 : return 10
+    if lat < 81.19801349 : return 9
+    if lat < 82.13956981 : return 8
+    if lat < 83.07199445 : return 7
+    if lat < 83.99173563 : return 6
+    if lat < 84.89166191 : return 5
+    if lat < 85.75541621 : return 4
+    if lat < 86.53536998 : return 3
+    if lat < 87.00000000 : return 2
+    else : return 1