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import math, time
def getLatLong():
"Returns URL for day/night picture"
# Define some 'constants'
ClientRecieveTime=time.time() * 1000
# QueryTimeZone = 10
QueryTimeZone = -time.timezone/3600
QueryTimeZoneOffsetMin = QueryTimeZone * 60
NISTSendTimeGMTms = ClientRecieveTime - ( QueryTimeZoneOffsetMin * 60 * 1000 )
# NIST start time in the query time zone
QueryTimeZoneOffset = ( QueryTimeZoneOffsetMin * 60 * 1000 )
# Replace this with "QueryTimeZoneOffset = ( -time.timezone * 60 * 1000 )"
# Client start time in some time zone
ClientRecieveTimems = ClientRecieveTime
# what timezone does your computer think it is? - in minutes
ClientTimeZone = QueryTimeZoneOffsetMin;
ClientNISTDelta = math.floor(NISTSendTimeGMTms - ClientRecieveTimems)
currTime = ClientRecieveTime + ClientNISTDelta # ThisMilliseconds
gmtTime = time.gmtime()
ssue = currTime / 1000
TwoPi = 2 * math.pi
EpochStart = 631065600
DaysSinceEpoch = (ssue - EpochStart)/ (24*3600)
RadsPerDay = TwoPi / 365.242191
Epsilon_g = 279.403303 * (TwoPi / 360)
OmegaBar_g = 282.768422 * (TwoPi / 360)
Eccentricity = 0.016713
MeanObliquity = 23.440592 * (TwoPi / 360);
# Calculate sun_ecliptic_longitude
N = RadsPerDay * DaysSinceEpoch
N = N % TwoPi
if N < 0:
N += TwoPi # This should never be executed, but never mind
M_Sun = N + Epsilon_g - OmegaBar_g
if M_Sun < 0:
M_Sun += TwoPi # This should never be executed either
# Now we solve keplers equation. For those who are interested keplers
# equation is all about plotting the orbit of an object on the
# elliptic plane.
E = M_Sun
while 1:
delta = E - (Eccentricity*math.sin(E)) - M_Sun
if (abs(delta) <= 1E-10):
break
E -= delta / (1 - (Eccentricity*math.cos(E)))
# End of the keplers equation solution
myLambda = OmegaBar_g + (2 * math.atan(math.sqrt((1+Eccentricity) / (1-Eccentricity)) * math.tan(E/2)))
# There, finished calculating the sun ecliptic longitude
# Now we calculate the ecliptic to equatorial (something or other)
sin_e = math.sin(MeanObliquity)
cos_e = math.cos(MeanObliquity)
alpha = math.atan2(math.sin(myLambda)*cos_e, math.cos(myLambda))
delta = math.asin(sin_e*math.sin(myLambda));
# End of ecliptic to equatorial
# We calculate the Julian date here, Python could probably do this better
# I leave it to the casual observer to replace the following few lines
y = gmtTime[0] # Year
m = gmtTime[1] # Month number
z = gmtTime[2] # Day number
A = y / 100
B = 2 - A + (A/4)
C = 365.25 * y
D = 30.6001 * (m+1)
JD = B + C + D + z + 1720994.5
T = (JD - 2451545) / 36525
T0 = ((((T + 2.5862E-5) * T) + 2400.051336) * T) + 6.697374558
T0 = T0 % 24
if T0 < 0:
T0 += 24
UT = (float(gmtTime[3])) + ((float(gmtTime[4]) + (float(gmtTime[5]) / 60)) / 60)
T0 += UT * 1.002737909
T0 = T0 % 24
if T0 < 0:
T0 += 24
tmp = alpha - ((TwoPi/24)*T0);
while tmp < -math.pi:
tmp += TwoPi
while tmp > math.pi:
tmp -= TwoPi
# Now calculate our longitude and latitude
lon = tmp * (360/TwoPi)
lat = delta * (360/TwoPi)
# Generate the path of the appropriate xearth image
lon = round(lon)
if (lon % 2 != 0):
if (lon > 0):
lon -= 1
else:
lon += 1
lon = round(lon/2) * 2
if lon <= -181:
lon = -180
if lon >= 181:
lon = 180
# lat is odd
lat = round(lat)
if (lat % 2 == 0):
if lat > 0:
lat -= 1
else:
lat += 1
# Need to do different calculations for negative and positive values of lat
# to emulate the way javascript handles rounding
if lat < 0:
lat = (round(int(lat/2) - 1) * 2) + 1
else:
lat = (round(lat/2 - 1) * 2) + 1
if lat <= -24:
lat = -23
if lat >= 24:
lat = 23
if lat < 0:
latStr = str(int(-lat)) + "S"
else:
latStr = str(int(lat)) + "N"
if lon < 0:
lonStr = str(int(-lon)) + "S"
else:
lonStr = str(int(lon)) + "N"
# url = "http://www.time.gov/" + getLatLong()
# return 'http://www.time.gov/images/xearths/11N/154N.jpg'
return "images/xearths/" + latStr + "/" + lonStr + ".jpg"
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