ash/forni/slade  1971 subroutine trnsit
revised 1977 to allow mutual occultations - j.f.chandler
main program for processing transit and occultation
observations

mocpar = 0 compar called in midst of least squares iteration
read all three data sets iobcon, iobs, iabs1 which become in
subroutines of compar iiobcn, iiobs, iiabs1
mocpar = 1 compar called at end of least squares iteration to
calculate dummy observations
read only iobcon which become in subroutines of compar iiobcn
procedural note - all coordinates are to be expressed in au,
au/day.  this means that values read from tape need not be
scaled (except moon), but that site coordinates must be.

Note: the arrays in REDOBS common for quantities to be read from
card or tape were all doubled to accommodate the scheme of up to 4
observables per card in TRNSIT.  The complete list is:
Resltb,Errorb,Ncodeb,Ihrb,Iminb,Secb,Atutsb,Ututsb,Clampb,Limbb,
Obsrvb,Imnthb,Idayb,Iyearb,Jdsb,Jdb,Ctatb,Ctrecb,Fdsb
However, the second halves of only two of these are ever used:
Errorb and Ncodeb.
savb(i,1), i=1,numsav,  saved precession-nutation,etc. from input
observation library tape
savb(i,2) i=1,numsav   these saved quantities from input observation
cards  (i.e., to be saved on output tape)

resltb(1,j) = time delay for radar observation (seconds)
right ascension for optical observation (sec.of time)
time that first limb of planet cuts first limb of sun
for transit observation (first part) (seconds)
resltb(2,j) = doppler shift for radar observation (cycles/sec)
declination for optical observatoon (sec.of arc)
time that second limb of planet cuts first limb of sun
for transit observation (first part) (seconds)

niobc,niobs,niabs1  indicate status of data sets  iiobc,
iiobs, iiabs1
-1  not to be read
0  ready to be read
1  already read
if  iiobc, iiobs, or iiabs1  are initially zero,  data set
is not read in any case.

type of observation specified by ibtrn
ibtrn=1 moon occults star
ibtrn=2 planet occults star
ibtrn=3 moon occults planet
ibtrn=4 planet transits sun
ibtrn=5 (not used)
ibtrn=6 planet occults planet (mutual event)
ibtrn=7 (reserved for black dot photographic obs)
ibtrn=8 planet occults planet (mid-time)
ibtrn=9 planet eclipses planet (mid-time)

ncodeb(i,1)=1  transit of first limb of planet only
ncodeb(i,1)=2  transit of first and second limb
ncodeb(i,1)=3  transit of second limb only
i= 1   transit is across first limb of sun
i= 2   transit is across second limb of sun

input units: ra,xmotra - hms, s/century
dec,xmotdc - dms, s/century  (arc)
prlx - arc-sec
rvel - km/s
for storage, ra and dec are converted to radians,
xmotra and xmotdc to radians/day
prlx to radians (1/au)
rvel to au/day