I have an older program that I wrote some time ago in VB then late updated for VB.Net. The program calculates the ephemerides of comets based on orbital elements downloaded from the Minor Planet Center website. I am now trying to make an iPhone/iPad application using the same idea and the same calculations. Unfortunately I am too new at objective-c that trying to convert the extensive calculations is proving quite difficult for me. I am hoping that someone can help me out and at least give me some pointers.
In particular, I have no idea how to accomplish this in objective-c:
Dim d1 As Date = DateSerial(yr_peri%, mo_peri%, dy_peri%)
dateser# = d1.ToOADate()
dateser# = dateser# + frac_day_peri#
jdperi# = 2415018.5 + dateser#
and this:
' Find Julian Day Number of start date & time
Dim d2 As Date = DateSerial(yr%, mo%, dd%)
Dim inputdate# = d2.ToOADate()
jdp# = inputdate + 2415018.5 ' use this day for phenom (rise/set) calcs
jd# = jdp# + fd# ' add fractional days
Here is the full VB version of the calculations in case it helps to understand the context:
Public Sub calc(ByVal cname$, ByVal qq#, ByVal e#, ByVal w#, ByVal om#, ByVal I#, ByVal yr_peri%, ByVal mo_peri%, ByVal day_peri#, ByVal abs_mag#, ByVal mag_n#)
Dim ep#
Dim dy_peri%, frac_day_peri#, dateser#, jdperi#
Dim yr%, mo%, dd%, fd#
Dim jdp#, jd#, interval#
Dim twi%, p_date#, ut#, er%
Dim t#, tt#, f#, p#, g#, q#, h#, r#
Dim a1#, a2#, b1#, b2#, c1#, c2#
Dim sdt#, a#, n#, period#, m#, e0#
Dim mrs#, frs%, ers0#, drs#, jrs%, mrs1#, e2#
Dim tv#, v#, r1#, r2#, w0#, s#, s0#
Dim x#, y#, z#, ls#, ms#, es#, th#, vs#, c#, th2000#
Dim rs#, xs#, ys#, zs#, xx#, yy#, radeg#, rad#, ra#, ras$
Dim dl#, dlm#, sd#, dec#, ds$
Dim cospsi#, psi#, elong#, cosbeta#, beta#, phase#
Dim ha#, ang#, az#, sinalt#, alt#, m1#, vl#
Dim Lati$, Longi$
Dim outpt$
'----------------------------------------------
'** AA=ASTRONOMICAL ALGORITHMS BY JEAN MEEUS **
'----------------------------------------------
counter% = 0
ep# = 23.439291 ' year 2000, AA page 214
cname$ = Trim(cname$)
'Get orbital elements
MainForm.grpEphemerides.Text = "Comet: " & cname$ & " - " + when$ ' Name
'qq# = Val(comet$(ind%, 1)) ' perihelion dist
'e# = Val(comet$(ind%, 2)) ' eccentricity (1=parabola)
'w# = Val(comet$(ind%, 3)) ' arg of perihelion - little omega
'om# = Val(comet$(ind%, 4)) ' long of ascending node - big omega
'I# = Val(comet$(ind%, 5)) ' inclination
'yr_peri% = Val(comet$(ind%, 6)) ' year
'mo_peri% = Val(comet$(ind%, 7)) ' month
'day_peri# = Val(comet$(ind%, 8)) ' day
'abs_mag# = Val(comet$(ind%, 9)) ' magnitude coef #1
'mag_n# = Val(comet$(ind%, 10)) ' magnitude coef #2
' Find JD of perihelion
dy_peri% = Int(day_peri#) ' day
frac_day_peri# = day_peri# - dy_peri% ' fractional day
Dim d1 As Date = DateSerial(yr_peri%, mo_peri%, dy_peri%)
dateser# = d1.ToOADate()
dateser# = dateser# + frac_day_peri#
jdperi# = 2415018.5 + dateser#
' Start date/time
yr% = Val(MainForm.txtYear.Text)
mo% = Val(MainForm.txtMonth.Text)
dd% = Val(MainForm.txtDay.Text)
fd# = Val(MainForm.txtHour.Text) / 24 + Val(MainForm.txtMin.Text) / 1440 + Val(MainForm.txtSec.Text) / 86400
lat# = Val(MainForm.txtLat.Text)
lon# = Val(MainForm.txtLon.Text)
' Find Julian Day Number of start date & time
Dim d2 As Date = DateSerial(yr%, mo%, dd%)
Dim inputdate# = d2.ToOADate()
jdp# = inputdate + 2415018.5 ' use this day for phenom (rise/set) calcs
jd# = jdp# + fd# ' add fractional days
interval# = Val(MainForm.txtInterval.Text)
' Determine if fixed times or rise/set phenomena
If MainForm.rdbFixedTimes.Checked = True Then
twi% = 0 ' use fixed times
Else
twi% = 1 ' use twilight times
interval# = Int(interval#) ' Set integer days (fraction doesn't make sense)
If interval# < 1 Then interval# = 1 ' make sure interval is at least one day
End If
'-----------
' Loop here
'-----------
While counter% <= Val(MainForm.txtNumSteps.Text)
If twi% = 1 Then
'Serial date of this calculation
p_date# = jdp# - 2415018.5
Call phenom(p_date#, ut#, er%) ' calcs for rise/set, returns er% (among other stuff)
jd# = Int(p_date#) + 2415018.5 + ut# / 24 + 1 / 2880
If er% = 1 Then ' er%=1 means no phenom (ex: sunrise) that day
ser_date# = jd# - 2415018.5
outpt$ = Format$(ser_date#, "mm/dd/yy") + " " + "No Rise/Set Phenomena on this Date"
GoTo No_phenom
End If
End If
' Days from perihelion of comet
t# = jd# - jdperi#
' Time (in Julian Centuries (36525 days)) since 1900 Jan 0.5 ET
' AA page 151
tt# = (jd# - 2451545.0#) / 36525.0!
'-------------- CALC F,G,H,P,Q,R (PP214 IN AA) ---------------
f# = Cos(dr# * om#)
p# = -Sin(dr# * om#) * Cos(dr# * I#)
g# = Sin(dr# * om#) * Cos(dr# * ep#)
q# = Cos(dr# * om#) * Cos(dr# * I#) * Cos(dr# * ep#) - Sin(dr# * I#) * Sin(dr# * ep#)
h# = Sin(dr# * om#) * Sin(dr# * ep#)
r# = Cos(dr# * om#) * Cos(dr# * I#) * Sin(dr# * ep#) + Sin(dr# * I#) * Cos(dr# * ep#)
'---------------- CALC A1,A2,B1,B2,C1,C2 (PP214 AA) -----------------
Call rec2pol(p#, f#, a1#, a2#)
Call rec2pol(q#, g#, b1#, b2#)
Call rec2pol(r#, h#, c1#, c2#)
'--------------- SIDEREAL TIME AT GREENWICH (PP84 AA) ----------------
' In degrees
sdt# = 280.46061837 + 360.98564736629 * (jd# - 2451545) + 0.000387933 * tt# * tt# - tt# * tt# * tt# / 38710000
sdt# = sdt# - 360 * Int(sdt# / 360)
'------------------- CALC ECCENTRIC & TRUE ANOMALY --------------------
If e# < 1 Then ' elliptical motion (pp214 AA)
a# = qq# / (1 - e#) ' semi major axis (AU)
n# = 0.9856076686 / a# / Sqrt(a#) ' mean motion (deg/day)
period# = 360 / n# / 365.25
MainForm.lblOrbitInf.Text = "Semimajor axis: " + Format$(a#, "#.000") + " AU Period: " + Format$(period#, "#.00") + " Years"
m# = n# * t# ' mean anomaly
e0# = rd# * e# ' "modified" eccentricity, page 187)
'ecc anomaly (page 195)
mrs# = m# * dr#
frs% = Sign(mrs#)
mrs# = Abs(mrs#) / (2 * pi#)
mrs# = (mrs# - Int(mrs#)) * 2 * pi# * frs%
If mrs# < 0 Then mrs# = mrs# + 2 * pi#
frs% = 1
If mrs# > pi# Then frs% = -1
If mrs# > pi# Then mrs# = 2 * pi# - mrs#
ers0# = pi# / 2
drs# = pi# / 4
For jrs% = 1 To 53
mrs1# = ers0# - e# * Sin(ers0#)
ers0# = ers0# + drs# * Sign(mrs# - mrs1#)
drs# = drs# / 2
Next jrs%
ers0# = ers0# * frs%
e2# = ers0# * rd#
'alpha# = (1 - e#) / (4 * e# + .5)
'beta# = m# / (8 * e# + 1)
'signbeta% = Sgn(beta#)
'cube# = beta# + signbeta% * Sqr(beta# ^ 2 + alpha# ^ 3)
'signz% = Sgn(cube#)
'zz# = signz% * (Abs(cube#)) ^ (1 / 3)
'ss0# = zz# - alpha# / 2
'ss# = ss0# - .078 * ss0# ^ 5 / (1 + e#)
'e1# = m# + e# * (3 * ss# - 4 * ss# ^ 3)
'loop1% = 0 ' counter
1040:
'e2# = e1# + (m# + e0# * Sin(dr# * e1#) - e1#) / (1 - e# * Cos(dr# * e1#))
'If Abs(e2# - e1#) < .0000000001 Or loop1% > 1000 Then ' e2#:ecc anom found
tv# = Sqrt((1 + e#) / (1 - e#)) * Tan(dr# * e2# / 2)
v# = 2 * rd# * Atan(tv#) ' true anomaly
r1# = a# * (1 - e# * Cos(dr# * e2#)) ' dist from sun AU
GoTo 2120
'Else
' e1# = e2# ' new ecc anomaly
' loop1% = loop1% + 1
' GoTo 1040
'End If
Else ' parabolic motion (pp225 AA)
MainForm.lblOrbitInf.Text = "This comet has a parabolic orbit-semimajor axis and period not determined"
w0# = 0.0364911624 * t# / qq# / Sqrt(qq#)
s# = 0
2110:
s0# = (2 * s# * s# * s# + w0#) / 3 / (s# * s# + 1)
If Abs(s# - s0#) > 0.0000000001 Then
s# = s0#
GoTo 2110
End If
s# = s0#
v# = 2 * rd# * Atan(s#) ' true anomaly
r1# = qq# * (1 + s# * s#) ' distance from sun (AU)
End If
2120:
v# = v# - 360 * Int(v# / 360) ' true anomaly
'r1#= dist from sun in au (above)
r2# = r1# * 92955807.0# ' Dist from sun (miles)
'-------- CALC HELIOCENTRIC RECT COORD OF COMET (PP215 AA) ----------
x# = r1# * a2# * Sin(dr# * (a1# + w# + v#))
y# = r1# * b2# * Sin(dr# * (b1# + w# + v#))
z# = r1# * c2# * Sin(dr# * (c1# + w# + v#))
'-------- CALC GEOCENTRIC RECT COORD OF SUN (PP151,152 AA) ---------
ls# = 280.46645 + 36000.76983 * tt# + 0.0003032 * tt# * tt#
ls# = ls# - 360 * Int(ls# / 360)
ms# = 357.5291 + 35999.0503 * tt# - 0.0001559 * tt# * tt# - 0.00000048 * tt# * tt# * tt#
ms# = ms# - 360 * Int(ms# / 360)
es# = 0.016708617 - 0.000042037 * tt# - 0.0000001236 * tt# * tt#
c# = (1.9146 - 0.004817 * tt# - 0.000014 * tt# * tt#) * Sin(dr# * ms#) + (0.019993 - 0.000101 * tt#) * Sin(2 * dr# * ms#) + 0.00029 * Sin(3 * dr# * ms#)
th# = ls# + c# ' TH is Sun's true longitude
vs# = ms# + c# ' VS is Sun's true anomaly
' pp152 AA
th2000# = th# - 0.01397 * (yr% + mo% / 12 + dd% / 365 - 2000) ' Sun true long referred to 2000
' sun's radius vector
rs# = (1.000001018 * (1 - es# * es#)) / (1 + es# * Cos(dr# * vs#))
' rectangular coord of sun (pp159 AA)
xs# = rs# * Cos(dr# * th2000#) ' Xsun
ys# = rs# * Sin(dr# * th2000#) * Cos(dr# * ep#) ' Ysun
zs# = rs# * Sin(dr# * th2000#) * Sin(dr# * ep#) ' Zsun
'------------- CALC GEOCENTRIC RA & DEC (PP 119 IN AFFC) --------------
xx# = xs# + x#
yy# = ys# + y#
Call rec2pol(xx#, yy#, radeg#, rad#)
ra# = radeg# / 15 ' RA of comet (2000) in hours
' 0 means time
ras$ = dec2ddmm(ra#, 0) ' ra in string form
'dist from comet to earth (au)
dl# = Sqrt((xs# + x#) ^ 2 + (ys# + y#) ^ 2 + (zs# + z#) ^ 2)
dlm# = dl# * 92955807.0# ' distance from earth in miles
sd# = (zs# + z#) / dl#
'DEC of comet (2000)
dec# = rd# * Atan(sd# / Sqrt(-sd# * sd# + 1))
' 1 means angle
ds$ = dec2ddmm(dec#, 1) ' dec in string form
' Calc elongation
cospsi# = (rs# * rs# + dl# * dl# - r1# * r1#) / (2 * rs# * dl#)
psi# = -Atan(cospsi# / Sqrt(-cospsi# * cospsi# + 1)) + pi# / 2
elong# = psi# * rd#
elong# = elong# - 360 * Int(elong# / 360)
' Calc phase
cosbeta# = (r1# * r1# + dl# * dl# - rs# * rs#) / (2 * r1# * dl#)
beta# = -Atan(cosbeta# / Sqrt(-cosbeta# * cosbeta# + 1)) + pi# / 2
phase# = beta# * rd#
phase# = phase# - 360 * Int(phase# / 360)
'------------ CALCULATE ALTITUDE & AZIMUTH (AA PP89) --------------
ha# = sdt# - lon# - radeg#
yy# = Sin(dr# * ha#)
xx# = (Cos(dr# * ha#) * Sin(dr# * lat#) - Tan(dr# * dec#) * Cos(dr# * lat#))
' rectangular to polar
Call rec2pol(xx#, yy#, ang#, rad#)
az# = ang# + 180
az# = az# - 360 * Int(az# / 360)
sinalt# = Sin(dr# * lat#) * Sin(dr# * dec#) + Cos(dr# * lat#) * Cos(dr# * dec#) * Cos(dr# * ha#)
alt# = rd# * Atan(sinalt# / Sqrt(1 - sinalt# * sinalt#))
'-------------- CALC EST MAGNITUDES & ORBITAL VELOCITY (AA PP 216) ---------------
m1# = abs_mag# + 5 * Log(dl#) / Log(10) + 2.5 * mag_n# * Log(r1#) / Log(10)
If e# < 1 Then
vl# = 42.1219 * Sqrt((1 / r1#) - (1 / (2 * a#))) ' elliptical orbital velocity, page 223
Else
vl# = 42.1219 * Sqrt(1 / r1#) ' parabolic orital velocity (my approximation)
End If
'------------- Stuff for output form -------------
Dim dt As DateTime = DateTime.FromOADate(dateser#)
MainForm.lblJDperi.Text = "Date of perihelion: " + dt.ToString("dd MMM yyyy hh:mm:ss") + " UTC JD: " + Format$(jdperi#, "#.00000")
Lati$ = " "
Longi$ = " "
If lat# > 0 Then Lati$ = "N " Else Lati$ = "S "
If lon# > 0 Then Longi$ = "W" Else Longi$ = "E"
MainForm.lblLoc.Text = "Observing Location: " + Format$(lat#, "+00.0000;-00.0000") + Chr(176) + Lati$ + Format$(lon#, "+000.0000;-000.0000") + Chr(176) + Longi$
'Serial date of this calculation
ser_date# = jd# - 2415018.5
' put the main info into a string
dt = DateTime.FromOADate(ser_date#)
outpt = dt.ToString("MM/dd/yy HH:mm:ss") & " " & ras$ & " " & ds$ & " " & Format$(alt#, "+00.0;-00.0") & Chr(176) & " " & Format$(az#, "000.0") & Chr(176)
outpt = outpt & " " & Format$(r1#, "00.0000") & " " & Format$(dl#, "00.0000") & " " & Format$(m1#, "+00.0;-00.0") + " " & Format$(elong#, "000.0") & Chr(176)
No_phenom:
' put the string into the list box
MainForm.lstPosition.Items.Add(outpt)
' put the "extra" data into the array
extra#(counter%, 0) = t# ' time to perih
extra#(counter%, 1) = vl# ' speed
extra#(counter%, 2) = phase# ' phase
extra#(counter%, 3) = v# ' true anomaly
' Increment counter
counter% = counter% + 1
' New JD
jd# = jd# + interval#
jdp# = jdp# + interval#
End While ' do again until done
End Sub
I appreciate any help or direction anyone can give on converting this function to objective-c.
Regards,
Keith
When working with dates in Objective-C you will often need to work with more than 1 class unlike other languages such as C#, Java and VB.NET. For creating a date from a string or getting a string from a date you will want to use the
NSDateFormatter. Now when attempting to modify or create a date with “components” (year,month,day etc.) you will want to useNSDateComponentsalong with the correctNSCalendar. The component solution looks like it will assist you with the DateSerial part. The linejdp# = inputdate + 2415018.5should be convertible (if it is seconds) to