Merge pull request #13 from Kelvinrr/master

added mars date support

plio/date/marstime.py

+'''
+Borrowed from Dave Pawlowski.
+(http://marstiming.readthedocs.io/en/latest/_modules/marstiming.html)
+
+Mars timing information based on MARS24: http://www.giss.nasa.gov/tools/mars24/help/algorithm.html
+
+Contains several functions for calculating Mars time parameters from Earth time and vice versa.
+Probably the most useful functions are:
+getMTfromTime: gets mars time data given a 6 element time list
+getSZAfromTime: gets the SZA from a 6 element time list and coordinates
+getLTfromTime: gets the LTST from a 6 element time list and longitude
+getUTCfromLS: Estimates the Earth time from LS and a Mars year
+'''
+
+import datetime
+from numpy import pi, floor,array,shape, cos, sin,ceil,arcsin,arccos,arange,abs
+from collections import namedtuple
+
+d2R = pi/180.
+
+def getJD(iTime):
+	'''Get the Julian date in seconds'''
+
+	offset = 2440587.5 #JD on 1/1/1970 00:00:00
+
+	year = iTime[0]
+	month = iTime[1]
+	day = iTime[2]
+	hour = iTime[3]
+	minute = iTime[4]
+	sec = iTime[5]
+	date = datetime.datetime(year,month,day,hour,minute,sec)
+
+	iTime = [1970,1,1,0,0,0]
+	year = iTime[0]
+	month = iTime[1]
+	day = iTime[2]
+	hour = iTime[3]
+	minute = iTime[4]
+	sec = iTime[5]
+	ref = datetime.datetime(year,month,day,hour,minute,sec)
+	deltaTime = (date-ref)
+	return deltaTime.total_seconds()/86400. + offset
+
+
+
+def getUTC(jd):
+	'''Get UTC given jd'''
+
+	offset = 2440587.5 #JD on 1/1/1970 00:00:00
+
+	iTime = [1970,1,1,0,0,0]
+	year = iTime[0]
+	month = iTime[1]
+	day = iTime[2]
+	hour = iTime[3]
+	minute = iTime[4]
+	sec = iTime[5]
+
+	d1970 = datetime.datetime(year,month,day,hour,minute,sec)
+	return d1970 + datetime.timedelta(seconds=((jd-offset)*86400.))
+
+
+def getJ2000(iTime):
+	'''get date in J2000 epoch.'''
+	jd = getJD(iTime)
+	T = (jd - 2451545.0)/36525 if iTime[0] < 1972 else 0
+
+	conversion = 64.184 + 59* T - 51.2* T**2 - 67.1* T**3 - 16.4* T**4
+
+	#convert to Terrestrial Time
+	jdTT = jd+(conversion/86400)
+
+	return jdTT - 2451545.0
+
+
+
+def getMarsParams(j2000):
+	'''Mars time parameters'''
+
+
+	Coefs = array(
+	[[0.0071,2.2353,49.409],
+	[0.0057,2.7543,168.173],
+	[0.0039,1.1177,191.837],
+	[0.0037,15.7866,21.736],
+	[0.0021,2.1354,15.704],
+	[0.0020,2.4694,95.528],
+	[0.0018,32.8493,49.095]])
+
+	dims = shape(Coefs)
+	#Mars mean anomaly:
+	M = 19.3870 + 0.52402075 * j2000
+
+	#angle of Fiction Mean Sun
+	alpha = 270.3863 + 0.52403840*j2000
+
+	#Perturbers
+	PBS = 0
+	for i in range(dims[0]):
+		PBS += Coefs[i,0]*cos(((0.985626* j2000 / Coefs[i,1]) + Coefs[i,2])*d2R)
+
+	#Equation of Center
+	vMinusM = ((10.691 + 3.0e-7 *j2000)*sin(M*d2R) + 0.623*sin(2*M*d2R) +
+	0.050*sin(3*M*d2R) + 0.005*sin(4*M*d2R) + 0.0005*sin(5*M*d2R) + PBS)
+
+	return M, alpha, PBS, vMinusM
+
+def getMTfromTime(iTime):
+	'''Get Mars time information.
+
+	:param iTime: 6 element time list [y,m,d,h,m,s]
+	:returns: a named tuple containing the LS value as well as
+	     several parameters necessary for other calculations
+
+	'''
+	if isinstance(iTime, datetime.datetime):
+		iTime = [iTime.year, iTime.month, iTime.day, iTime.hour, iTime.minute, iTime.second]
+
+	DPY = 686.9713
+	refTime = [1955,4,11,10,56,0] #Mars year 1
+	rDate = getJD(refTime)
+	thisTime = getJD(iTime)
+	year = floor((thisTime - rDate)/DPY)+1
+
+	j2000 = getJ2000(iTime)
+	M,alpha,PBS,vMinusM = getMarsParams(j2000)
+
+	LS = (alpha + vMinusM)
+
+	while LS > 360:
+		LS -= 360
+
+	if LS < 0:
+		LS = 360. + 360.*(LS/360. - ceil(LS/360.0))
+
+	EOT = 2.861*sin(2*LS*d2R)-0.071*sin(4*LS*d2R)+0.002*sin(6*LS*d2R)-vMinusM
+
+	MTC = (24*(((j2000 - 4.5)/1.027491252)+44796.0 - 0.00096 )) % 24
+	subSolarLon = ((MTC+EOT*24/360.)*(360/24.)+180) % 360
+	solarDec = (arcsin(0.42565*sin(LS*d2R))/d2R+0.25*sin(LS*d2R))
+
+	data = namedtuple('data','ls year M alpha PBS vMinusM MTC EOT subSolarLon solarDec')
+	d1 = data(ls = LS,year=year,M=M,alpha=alpha,PBS=PBS,vMinusM=vMinusM,MTC=MTC,EOT=EOT,
+		subSolarLon=subSolarLon,solarDec=solarDec)
+
+	return d1
+
+def getUTCfromLS(marsyear,LS):
+	'''Get a UTC starting with an estimate of LS using an orbit angle approximation
+	then iteratively closing in on the correct LS by incrementing the a day first and then hour.
+
+	:param marsyear: an int mars year
+	:param ls: ls- mars solar longitude
+	:returns: UTC1 (python datetime)'''
+
+	#Get LS to within this value:
+	error = 0.001
+	DPY = 686.9713
+
+	###Start with estimate
+
+	refTime = [1955,4,11,10,56,0] #Mars year 1
+	rDate = getJD(refTime)
+	iTime = getUTC(rDate+(marsyear-1)*DPY) #LS 0 of given mars year
+
+	#Now we have a guess, iterate over the day to get closer and closer.
+
+	thisTime = [iTime.year,iTime.month,iTime.day,iTime.hour,iTime.minute,iTime.second]
+	thisLS = 0
+
+	factor = 1 #do we increment up or down?
+	iTry = 0
+	dt = 60 #hours.  This will get smaller as we get closer
+	counter = 0
+	olddiff = 1000.
+	diff = 100
+	while diff > error:
+
+		iTime = iTime+factor*datetime.timedelta(hours=dt)
+		thisTime = [iTime.year,iTime.month,iTime.day,iTime.hour,iTime.minute,iTime.second]
+		timedata = getMTfromTime(thisTime)
+		thisLS,myear = timedata.ls, timedata.year
+		diff = abs(thisLS - LS)
+
+
+		if diff > olddiff:
+			factor = -1*factor
+			counter += 1
+			if counter > 1:
+				dt = dt/60.
+
+		olddiff = diff
+		iTry += 1
+
+
+		if iTry > 1000:
+			print('Problem getting UTC from Ls in 2nd diff loop')
+			print('Quitting if function getUTCfromLS...')
+			exit(1)
+
+	return iTime
+
+def getSZAfromTime(time,lon,lat):
+	'''Get SZA from Earth time and Mars coordinates.
+
+	:param the time: [y,m,d,h,m,s] or datetime object
+	:param lon: the longitude in degrees
+	:param lat: the latitude in degrees
+	:returns: the solar zenith angle (float)'''
+
+
+	if type(time) == datetime.datetime:
+		time = [time.year,time.month,time.day,time.hour,time.minute,time.second]
+
+	timedata = getMTfromTime(time)
+
+	SZA = arccos(sin(timedata.solarDec*d2R)*sin(lat*d2R)+
+		cos(timedata.solarDec*d2R)*cos(lat*d2R)*cos((lon-timedata.subSolarLon)*d2R))/d2R
+
+	return SZA
+
+def SZAGetTime(sza,date, lon, lat):
+	'''Find the time on a given date and location when the SZA is a given value.
+
+	:param sza: Solar zenith angle in degrees
+	:param date: [y,m,d]<
+	:param lon: the longitude in degrees
+	:param lat: the latitude in degrees
+	:returns: A python datetime object
+	'''
+	thisDate = datetime.datetime(date[0],date[1],date[2])
+
+
+	count = 0
+	counter = 0
+	error = 1
+	factor = 1
+	dt = 15 #minutes
+	thisSza = getSZAfromTime(thisDate,lon,lat)
+	diff = abs(thisSza - sza)
+	while diff > error:
+		thisDate += factor*datetime.timedelta(minutes=dt)
+		thisSza = getSZAfromTime(thisDate,lon,lat)
+		newdiff = abs(thisSza - sza)
+		if newdiff > diff:
+			factor = -1*factor
+			counter += 1
+			if counter > 1:  #Wait until counter is > 1 in case we start off going the wrong way!
+				dt = dt/2.
+
+		count += 1
+		if abs(diff - newdiff)/2. < error and counter > 5:
+			print('this location doesnt reach the given SZA.  Returning closest value... {:f}'.format(thisSza))
+			return thisDate, thisSza
+
+		diff = newdiff
+
+	return thisDate, thisSza
+
+
+def getLTfromTime(iTime,lon):
+	'''The mars local solar time from an earth time and mars longitude.
+
+	:param iTime: 6 element list: [y,m,d,h,m,s]
+	:param lon: the longitude in degrees
+	:returns: The local time (float)'''
+
+	timedata = getMTfromTime(iTime)
+	LMST = timedata.MTC-lon*(24/360.)
+	LTST = LMST + timedata.EOT*(24/360.)
+
+	return LTST

plio/date/tests/test_marstime.py

+import numpy as np
+import unittest
+import datetime
+
+from .. import marstime
+
+class TestMarsTime(unittest.TestCase):
+    def equality_test(self):
+        earth = marstime.getUTCfromLS(24, 130)
+        mars = marstime.getMTfromTime(earth)
+        assert(earth.date() == marstime.getUTCfromLS(mars.year,mars.ls).date())
+
+    def test_J2000(self):
+        iTime = [2001,11,13,2,45,2]
+        testJD = marstime.getJ2000(iTime)
+        callibration = 58891502.000000 #test should be this value.
+        diff = testJD - callibration
+        print(testJD)
+        print(diff)
+        self.assertTrue(diff == -58890820.38465065)
+
+
+    def test_UTC(self):
+        jd = 2452226.614606
+        date = marstime.getUTC(jd)
+        callibration = datetime.datetime(2001,11,13,2,45,2)
+        diff = callibration - date
+        self.assertTrue(str(diff) == '0:00:00.041599')
+
+
+    def test_LS(self):
+        iTime = [2000,1,6,0,0,0]
+        lsdata = marstime.getMTfromTime(iTime)
+        ls = lsdata.ls
+        year = lsdata.year
+        callibration = 277.18677
+        diff = ls - callibration
+        print(diff)
+        self.assertAlmostEqual(diff, 0.0)
+
+    def test_SZA(self):
+        '''test getSZAfromTime'''
+        itime = [2000,1,6,0,0,0]
+        lon = 0.0
+        lat = 0.0
+        expected = 154.261908004
+        sza = marstime.getSZAfromTime(itime,lon,lat)
+        self.assertAlmostEqual(sza, expected)
+
+    def test_SZAGetTime(self):
+        out = marstime.SZAGetTime(0, [1,1,1], 0,0)
+        self.assertAlmostEqual(out[1], 9.454213735250395)
+
+
+    def test_LTfromTime(self):
+        '''test getLTfromTime function'''
+        iTime = [2000,1,6,0,0,0]
+        lon = 0.0
+        LTST = marstime.getLTfromTime(iTime,lon)
+        expected = 23.648468934
+        self.assertAlmostEqual(LTST, expected)