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CPR calculator: fixed order of operations bug on modulus operator in longitude calculation of global resolver. Test case passes 100%.

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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.
This commit is contained in:
Nick Foster 2012-06-18 18:18:47 -07:00
parent cbdef224c1
commit 6882329f8d
1 changed files with 19 additions and 29 deletions
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48
python/cpr.py
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@ -73,7 +73,7 @@ def dlon(declat_in, ctype, surface):
def decode_lat(enclat, ctype, my_lat, surface): def decode_lat(enclat, ctype, my_lat, surface):
tmp1 = dlat(ctype, surface) tmp1 = dlat(ctype, surface)
tmp2 = float(enclat) / (2**nbits(surface)) tmp2 = float(enclat) / (2**nbits(surface))
j = math.floor(my_lat/tmp1) + math.floor(0.5 + (mod(my_lat, tmp1) / tmp1) - tmp2) j = math.floor(my_lat/tmp1) + math.floor(0.5 + ((my_lat % tmp1) / tmp1) - tmp2)
# print "dlat gives " + "%.6f " % tmp1 + "with j = " + "%.6f " % j + " and tmp2 = " + "%.6f" % tmp2 + " given enclat " + "%x" % enclat # print "dlat gives " + "%.6f " % tmp1 + "with j = " + "%.6f " % j + " and tmp2 = " + "%.6f" % tmp2 + " given enclat " + "%x" % enclat
return tmp1 * (j + tmp2) return tmp1 * (j + tmp2)
@ -81,17 +81,11 @@ def decode_lat(enclat, ctype, my_lat, surface):
def decode_lon(declat, enclon, ctype, my_lon, surface): def decode_lon(declat, enclon, ctype, my_lon, surface):
tmp1 = dlon(declat, ctype, surface) tmp1 = dlon(declat, ctype, surface)
tmp2 = float(enclon) / (2.0**nbits(surface)) tmp2 = float(enclon) / (2.0**nbits(surface))
m = math.floor(my_lon / tmp1) + math.floor(0.5 + (mod(my_lon, tmp1) / tmp1) - tmp2) m = math.floor(my_lon / tmp1) + math.floor(0.5 + ((my_lon % tmp1) / tmp1) - tmp2)
# print "dlon gives " + "%.6f " % tmp1 + "with m = " + "%.6f " % m + " and tmp2 = " + "%.6f" % tmp2 + " given enclon " + "%x" % enclon # print "dlon gives " + "%.6f " % tmp1 + "with m = " + "%.6f " % m + " and tmp2 = " + "%.6f" % tmp2 + " given enclon " + "%x" % enclon
return tmp1 * (m + tmp2) return tmp1 * (m + tmp2)
def mod(a, b):
if a < 0:
return (a+360.0) % b
return a%b
def cpr_resolve_local(my_location, encoded_location, ctype, surface): def cpr_resolve_local(my_location, encoded_location, ctype, surface):
[my_lat, my_lon] = my_location [my_lat, my_lon] = my_location
[enclat, enclon] = encoded_location [enclat, enclon] = encoded_location
@ -101,7 +95,7 @@ def cpr_resolve_local(my_location, encoded_location, ctype, surface):
return [decoded_lat, decoded_lon] return [decoded_lat, decoded_lon]
def cpr_resolve_global(evenpos, oddpos, mostrecent, surface): #ok this is considered working, tentatively def cpr_resolve_global(evenpos, oddpos, mostrecent, surface):
dlateven = dlat(0, surface) dlateven = dlat(0, surface)
dlatodd = dlat(1, surface) dlatodd = dlat(1, surface)
if surface is True: if surface is True:
@ -112,17 +106,16 @@ def cpr_resolve_global(evenpos, oddpos, mostrecent, surface): #ok this is consid
evenpos = [float(evenpos[0]), float(evenpos[1])] evenpos = [float(evenpos[0]), float(evenpos[1])]
oddpos = [float(oddpos[0]), float(oddpos[1])] oddpos = [float(oddpos[0]), float(oddpos[1])]
#print "Even position: %x, %x\nOdd position: %x, %x" % (evenpos[0], evenpos[1], oddpos[0], oddpos[1],) j = math.floor(((nz(1)*evenpos[0] - nz(0)*oddpos[0])/scalar) + 0.5) #latitude index
j = math.floor(((59.*evenpos[0] - 60.*oddpos[0])/scalar) + 0.5) #latitude index rlateven = dlateven * ((j % nz(0))+evenpos[0]/scalar)
if j < 0: rlatodd = dlatodd * ((j % nz(1))+ oddpos[0]/scalar)
# print "ERROR J IS %f" % j
j += 59 #i don't know why this works
rlateven = dlateven * (mod(j, 60)+evenpos[0]/scalar) #limit to -90, 90
rlatodd = dlatodd * (mod(j, 59)+ oddpos[0]/scalar) if rlateven > 270.0:
rlateven -= 360.0
#print "Rlateven: %f Rlatodd: %f" % (rlateven, rlatodd) if rlatodd > 270.0:
rlatodd -= 360.0
#This checks to see if the latitudes of the reports straddle a transition boundary #This checks to see if the latitudes of the reports straddle a transition boundary
#If so, you can't get a globally-resolvable location. #If so, you can't get a globally-resolvable location.
@ -134,23 +127,19 @@ def cpr_resolve_global(evenpos, oddpos, mostrecent, surface): #ok this is consid
rlat = rlateven rlat = rlateven
else: else:
rlat = rlatodd rlat = rlatodd
#print rlat
if rlat > 270.0:
rlat = rlat - 360.0
dl = dlon(rlat, mostrecent, surface) dl = dlon(rlat, mostrecent, surface)
nlthing = nl(rlat) nlthing = nl(rlat)
ni = max(nlthing - mostrecent, 1) ni = max(nlthing - mostrecent, 1)
m = math.floor(((evenpos[1]*(nlthing-1)-oddpos[1]*(nlthing))/scalar)+0.5) #longitude index, THIS LINE IS CORRECT m = math.floor(((evenpos[1]*(nlthing-1)-oddpos[1]*(nlthing))/scalar)+0.5) #longitude index
if mostrecent == 0: if mostrecent == 0:
enclon = evenpos[1] enclon = evenpos[1]
else: else:
enclon = oddpos[1] enclon = oddpos[1]
rlon = dl * (mod(ni+m, ni)+enclon/2**nbits(surface)) rlon = dl * (((ni+m) % ni)+enclon/2**nbits(surface))
if rlon > 180: if rlon > 180:
rlon = rlon - 360.0 rlon = rlon - 360.0
@ -257,9 +246,8 @@ def cpr_encode(lat, lon, ctype, surface):
scalar = float(2**17) scalar = float(2**17)
dlati = float(dlat(ctype, False)) dlati = float(dlat(ctype, False))
yz = math.floor(scalar * (mod(lat, dlati)/dlati) + 0.5) yz = math.floor(scalar * ((lat % dlati)/dlati) + 0.5)
rlat = dlati * ((yz / scalar) + math.floor(lat / dlati)) rlat = dlati * ((yz / scalar) + math.floor(lat / dlati))
#print "lat: %f dlati: %f yz: %f rlat: %f" % (lat, dlati, yz, rlat)
nleo = nl_eo(rlat, ctype) nleo = nl_eo(rlat, ctype)
if nleo == 0: if nleo == 0:
@ -267,10 +255,10 @@ def cpr_encode(lat, lon, ctype, surface):
else: else:
dloni = 360.0 / nl_eo(rlat, ctype) dloni = 360.0 / nl_eo(rlat, ctype)
xz = math.floor(scalar * (mod(lon, dloni)/dloni) + 0.5) xz = math.floor(scalar * ((lon % dloni)/dloni) + 0.5)
yz = int(mod(yz, scalar)) yz = int(yz % scalar)
xz = int(mod(xz, scalar)) xz = int(xz % scalar)
return (yz, xz) #lat, lon return (yz, xz) #lat, lon
@ -307,6 +295,8 @@ if __name__ == '__main__':
#print "Lat: %f Lon: %f" % (ac_lat, ac_lon) #print "Lat: %f Lon: %f" % (ac_lat, ac_lon)
if abs(odddeclat - ac_lat) > threshold or abs(odddeclon - ac_lon) > threshold: if abs(odddeclat - ac_lat) > threshold or abs(odddeclon - ac_lon) > threshold:
#print "odddeclat: %f ac_lat: %f" % (odddeclat, ac_lat)
#print "odddeclon: %f ac_lon: %f" % (odddeclon, ac_lon)
raise Exception("CPR test failure: global decode error greater than threshold") raise Exception("CPR test failure: global decode error greater than threshold")
(evendeclat, evendeclon) = cpr_resolve_local([ac_lat, ac_lon], [evenenclat, evenenclon], False, False) (evendeclat, evendeclon) = cpr_resolve_local([ac_lat, ac_lon], [evenenclat, evenenclon], False, False)