CPR calculator: fixed order of operations bug on modulus operator in longitude calculation of global resolver. Test case passes 100%.
This has the interesting side effect of fixing the "boundary straddle" problem previously seen. Possibly also fixes the bad positions sometimes seen in real aircraft.
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Nick Foster
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cbdef224c1
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6882329f8d
@ -73,7 +73,7 @@ def dlon(declat_in, ctype, surface):
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def decode_lat(enclat, ctype, my_lat, surface):
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tmp1 = dlat(ctype, surface)
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tmp2 = float(enclat) / (2**nbits(surface))
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j = math.floor(my_lat/tmp1) + math.floor(0.5 + (mod(my_lat, tmp1) / tmp1) - tmp2)
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j = math.floor(my_lat/tmp1) + math.floor(0.5 + ((my_lat % tmp1) / tmp1) - tmp2)
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# print "dlat gives " + "%.6f " % tmp1 + "with j = " + "%.6f " % j + " and tmp2 = " + "%.6f" % tmp2 + " given enclat " + "%x" % enclat
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return tmp1 * (j + tmp2)
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@ -81,17 +81,11 @@ def decode_lat(enclat, ctype, my_lat, surface):
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def decode_lon(declat, enclon, ctype, my_lon, surface):
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tmp1 = dlon(declat, ctype, surface)
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tmp2 = float(enclon) / (2.0**nbits(surface))
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m = math.floor(my_lon / tmp1) + math.floor(0.5 + (mod(my_lon, tmp1) / tmp1) - tmp2)
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m = math.floor(my_lon / tmp1) + math.floor(0.5 + ((my_lon % tmp1) / tmp1) - tmp2)
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# print "dlon gives " + "%.6f " % tmp1 + "with m = " + "%.6f " % m + " and tmp2 = " + "%.6f" % tmp2 + " given enclon " + "%x" % enclon
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return tmp1 * (m + tmp2)
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def mod(a, b):
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if a < 0:
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return (a+360.0) % b
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return a%b
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def cpr_resolve_local(my_location, encoded_location, ctype, surface):
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[my_lat, my_lon] = my_location
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[enclat, enclon] = encoded_location
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@ -101,7 +95,7 @@ def cpr_resolve_local(my_location, encoded_location, ctype, surface):
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return [decoded_lat, decoded_lon]
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def cpr_resolve_global(evenpos, oddpos, mostrecent, surface): #ok this is considered working, tentatively
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def cpr_resolve_global(evenpos, oddpos, mostrecent, surface):
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dlateven = dlat(0, surface)
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dlatodd = dlat(1, surface)
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if surface is True:
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@ -112,17 +106,16 @@ def cpr_resolve_global(evenpos, oddpos, mostrecent, surface): #ok this is consid
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evenpos = [float(evenpos[0]), float(evenpos[1])]
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oddpos = [float(oddpos[0]), float(oddpos[1])]
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#print "Even position: %x, %x\nOdd position: %x, %x" % (evenpos[0], evenpos[1], oddpos[0], oddpos[1],)
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j = math.floor(((nz(1)*evenpos[0] - nz(0)*oddpos[0])/scalar) + 0.5) #latitude index
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j = math.floor(((59.*evenpos[0] - 60.*oddpos[0])/scalar) + 0.5) #latitude index
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if j < 0:
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# print "ERROR J IS %f" % j
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j += 59 #i don't know why this works
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rlateven = dlateven * ((j % nz(0))+evenpos[0]/scalar)
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rlatodd = dlatodd * ((j % nz(1))+ oddpos[0]/scalar)
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rlateven = dlateven * (mod(j, 60)+evenpos[0]/scalar)
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rlatodd = dlatodd * (mod(j, 59)+ oddpos[0]/scalar)
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#print "Rlateven: %f Rlatodd: %f" % (rlateven, rlatodd)
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#limit to -90, 90
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if rlateven > 270.0:
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rlateven -= 360.0
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if rlatodd > 270.0:
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rlatodd -= 360.0
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#This checks to see if the latitudes of the reports straddle a transition boundary
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#If so, you can't get a globally-resolvable location.
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@ -134,23 +127,19 @@ def cpr_resolve_global(evenpos, oddpos, mostrecent, surface): #ok this is consid
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rlat = rlateven
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else:
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rlat = rlatodd
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#print rlat
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if rlat > 270.0:
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rlat = rlat - 360.0
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dl = dlon(rlat, mostrecent, surface)
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nlthing = nl(rlat)
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ni = max(nlthing - mostrecent, 1)
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m = math.floor(((evenpos[1]*(nlthing-1)-oddpos[1]*(nlthing))/scalar)+0.5) #longitude index, THIS LINE IS CORRECT
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m = math.floor(((evenpos[1]*(nlthing-1)-oddpos[1]*(nlthing))/scalar)+0.5) #longitude index
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if mostrecent == 0:
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enclon = evenpos[1]
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else:
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enclon = oddpos[1]
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rlon = dl * (mod(ni+m, ni)+enclon/2**nbits(surface))
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rlon = dl * (((ni+m) % ni)+enclon/2**nbits(surface))
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if rlon > 180:
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rlon = rlon - 360.0
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@ -257,9 +246,8 @@ def cpr_encode(lat, lon, ctype, surface):
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scalar = float(2**17)
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dlati = float(dlat(ctype, False))
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yz = math.floor(scalar * (mod(lat, dlati)/dlati) + 0.5)
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yz = math.floor(scalar * ((lat % dlati)/dlati) + 0.5)
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rlat = dlati * ((yz / scalar) + math.floor(lat / dlati))
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#print "lat: %f dlati: %f yz: %f rlat: %f" % (lat, dlati, yz, rlat)
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nleo = nl_eo(rlat, ctype)
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if nleo == 0:
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@ -267,10 +255,10 @@ def cpr_encode(lat, lon, ctype, surface):
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else:
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dloni = 360.0 / nl_eo(rlat, ctype)
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xz = math.floor(scalar * (mod(lon, dloni)/dloni) + 0.5)
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xz = math.floor(scalar * ((lon % dloni)/dloni) + 0.5)
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yz = int(mod(yz, scalar))
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xz = int(mod(xz, scalar))
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yz = int(yz % scalar)
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xz = int(xz % scalar)
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return (yz, xz) #lat, lon
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@ -307,6 +295,8 @@ if __name__ == '__main__':
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#print "Lat: %f Lon: %f" % (ac_lat, ac_lon)
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if abs(odddeclat - ac_lat) > threshold or abs(odddeclon - ac_lon) > threshold:
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#print "odddeclat: %f ac_lat: %f" % (odddeclat, ac_lat)
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#print "odddeclon: %f ac_lon: %f" % (odddeclon, ac_lon)
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raise Exception("CPR test failure: global decode error greater than threshold")
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(evendeclat, evendeclon) = cpr_resolve_local([ac_lat, ac_lon], [evenenclat, evenenclon], False, False)
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