LATITUDE_LONGITUDE_SUBROUTINES.agc
### FILE="Main.annotation"
## Copyright: Public domain.
## Filename: LATITUDE_LONGITUDE_SUBROUTINES.agc
## Purpose: Part of the source code for Artemis (i.e., Colossus 3),
## build 072. This is for the Command Module's (CM)
## Apollo Guidance Computer (AGC), for
## Apollo 15-17.
## Assembler: yaYUL
## Contact: Sergio Navarro <sergionavarrog@gmail.com>
## Website: www.ibiblio.org/apollo/index.html
## Page Scans: www.ibiblio.org/apollo/ScansForConversion/Artemis072/
## Mod history: 2009-09-03 SN Adapted from corresponding Comanche 055 file.
## 2009-09-04 JL Fixed typos.
## 2010-02-20 RSB Un-##'d this header.
## 2010-04-13 JL Fixed a typo (' instead of #).
## 2010-08-15 JL Fixed indentation.
## 2017-02-05 RSB Proofed comment text by diff'ing vs Comanche 55
## and corrected errors found.
## 2017-03-15 RSB Comment-text fixes identified in 5-way
## side-by-side diff of Luminary 69/99/116/131/210.
## Page 1236
# SUBROUTINE TO CONVERT RAD VECTOR AT GIVEN TIME TO LAT,LONG AND ALT
#
# CALLING SEQUENCE
#
# L-1 CALL
# L LAT-LONG
#
# SUBROUTINES USED
#
# R-TO-RP, ARCTAN, SETGAMMA, SETRE
#
# ERASABLE INIT. REQ.
#
# AXO, -AYO, AZO, TEPHEM (SET AT LAUNCH TIME)
# ALPHAV = POSITION VECTOR METERS B-29
# MPAC -- TIME (CSECS B-28)
# ERADFLAG =1, TO COMPUTE EARTH RADIUS, =0 FOR FIXED EARTH RADIUS
# LUNAFLAG=0 FOR EARTH, 1 FOR MOON
#
# OUTPUT
#
# LATITUDE IN LAT (REVS. B-0)
# LONGITUDE IN LONG (REVS. B-0)
# ALTITUDE IN ALT METERS B-29
SETLOC LATLONG
BANK
COUNT* $$/LT-LG
EBANK= ALPHAV
LAT-LONG STQ SETPD
INCORPEX
0D
STOVL 6D # SAVE TIME IN 6-7D FOR R-TO-RP
ALPHAV
PUSH ABVAL # 0-5D= R FOR R-TO-RP
STODL ALPHAM # ABS. VALUE OF R FOR ALT FORMULA BELOW
ZEROVEC # SET MPAC=0 FOR EARTH, NON-ZERO FOR MOON
BOFF COS # USE COS(0) TO GET NON-ZERO IN MPAC
LUNAFLAG # 0=EARTH,1=MOON
CALLRTRP
CALLRTRP CALL
R-TO-RP # RP VECTOR CONVERTED FROM R B-29
UNIT # UNIT RP B-1
STCALL ALPHAV # U2= 1/2 SINL FOR SETRE SUBR BELOW
SETGAMMA # SET GAMMA=B2/A2 FOR EARTH, =1 FOR MOON
CALL # SCALED B-1
SETRE # CALC RE METERS B-29
DLOAD DSQ
ALPHAV
PDDL DSQ
ALPHAV +2
DAD SQRT
DMP SL1R
## Page 1237
GAMRP
STODL COSTH # COS(LAT) B-1
ALPHAV +4
STCALL SINTH # SIN(LAT) B-1
ARCTAN
STODL LAT # LAT B0
ALPHAV
STODL COSTH # COS(LONG) B-1
ALPHAV +2
STCALL SINTH # SIN(LONG) B-1
ARCTAN
STODL LONG # LONG. REVS B-0 IN RANGE -1/2 TO 1/2
ALPHAM
DSU # ALT= R-RE METERS B-29
ERADM
STCALL ALT # EXIT WITH ALT METERS B-29
INCORPEX
## Page 1238
# SUBROUTINE TO CONVERT LAT,LONG,ALT AT GIVEN TIME TO RADIUS VECTOR
#
# CALLING SEQUENCE
#
# L-1 CALL
# L LALOTORV
#
# SUBROUTINES USED
#
# SETGAMMA, SETRE, RP-TO-R
#
# ERASABLE INIT. REQ.
#
# AXO, AYO, AZO, TEPHEM SET AT LAUNCH TIME
# LAT -- LATITUDE (REVS B0)
# LONG -- LONGITUDE (REVS B0)
# ALT -- ALTITUDE (METERS) B-29
# MPAC -- TIME (CSECS B-28)
# ERADFLAG =1 TO COMPUTE EARTH RADIUS, =0 FOR FIXED EARTH RADIUS
# LUNAFLAG=0 FOR EARTH, 1 FOR MOON
#
# OUTPUT
#
# R-VECTOR IN ALPHAV (METERS B-29)
LALOTORV STQ SETPD # LAT,LONG,ALT TO R VECTOR
INCORPEX
0D
STCALL 6D # 6-7D = TIME FOR RP-TO-R
SETGAMMA # GAMMA = B2/A2 FOR EARTH, 1 FOR MOON B-1
DLOAD SIN # COS(LONG)COS(LAT) IN MPAC
LAT # UNIT RP = SIN(LONG)COS(LAT) 2-3D
DMPR PDDL # PD 2 GAMMA*SIN(LAT) 0-1D
GAMRP
LAT # 0-1D = GAMMA*SIN(LAT) B-2
COS PDDL # PD4 2-3D = COS(LAT) B-1 TEMPORARILY
LONG
SIN DMPR # PD 2
PDDL COS # PD 4 2-3D = SIN(LONG)COS(LAT) B-2
LAT
PDDL COS # PD 6 4-5D = COS(LAT) B-1 TEMPORARILY
LONG
DMPR VDEF # PD4 MPAC = COS(LONG)COS(LAT) B-2
UNIT PUSH # 0-5D = UNIT RP FOR RP-TO-R SUBR.
STCALL ALPHAV # ALPHAV +4= SINL FOR SETRE SUBR.
SETRE # RE METERS B-29
DLOAD BOFF # SET MPAC = 0 FOR EARTH, NON-ZERO FOR MOON
ZEROVEC
LUNAFLAG
CALLRPRT
COS # USE COS(0) TO GET NON-ZERO IN MPAC
CALLRPRT CALL
RP-TO-R # EXIT WITH UNIT R VECTOR IN MPAC
STODL ALPHAV
ERADM
## Page 1239
DAD VXSC # (RE + ALT)(UNIT R) METERS B-30
ALT
ALPHAV
VSL1 # R METERS B-29
STCALL ALPHAV # EXIT WITH R IN METERS B-29
INCORPEX
# SUBROUTINE TO COMPUTE EARTH RADIUS
#
# INPUT
#
# 1/2 SIN LAT IN ALPHAV +4
#
# OUTPUT
#
# EARTH RADIUS IN ERADM AND MPAC (METERS B-29)
GETERAD DLOAD DSQ
ALPHAV +4 # SIN**2(L)
SL1 BDSU
DP1/2 # COS**2(L)
DMPR BDSU
EE
DP1/2
BDDV SQRT
B2XSC
SR4R
STORE ERADM
RVQ
# THE FOLLOWING CONSTANTS WERE COMPUTED WITH A=6378166, B=6356784 METERS
# B2XSC = B**2 SCALED B-51
# B2/A2 = B**2/A**2 SCALED B-1
# EE = (1-B**2/A**2) SCALED B-0
B2XSC 2DEC .0179450689 # B**2 SCALED B-51
DP1/2 = XUNIT
B2/A2 2DEC .9933064884 B-1 # GAMMA= B**2/A**2 B-1
EE 2DEC 6.6935116 E-3 # (1-B**2/A**2) B-0
ERAD 2DEC 6373338 B-29 # PAD RADIUS
## Page 1240
# ARCTAN SUBROUTINE
#
# CALLING SEQUENCE
#
# SIN THETA IN SINTH B-1
# COS THETA IN COSTH B-1
# CALL ARCTAN
#
# OUTPUT
# ARCTAN THETA IN MPAC AND THETA B-0 IN RANGE -1/2 TO +1/2
ARCTAN BOV
CLROVFLW
CLROVFLW DLOAD DSQ
SINTH
PDDL DSQ
COSTH
DAD
BZE SQRT
ARCTANXX # ATAN=0/0 SET THETA=0
BDDV BOV
SINTH
ATAN=90
SR1 ASIN
STORE THETA
PDDL BMN
COSTH
NEGCOS
DLOAD RVQ
NEGCOS DLOAD DCOMP
BPL DAD
NEGOUT
DP1/2
ARCTANXX STORE THETA
RVQ
NEGOUT DSU GOTO
DP1/2
ARCTANXX
ATAN=90 DLOAD SIGN
LODP1/4
SINTH
STORE THETA
RVQ
2DZERO = DPZERO
## Page 1241
# ..... SETGAMMA SUBROUTINE .....
# SUBROUTINE TO SET GAMMA FOR THE LAT-LONG AND LALOTORV SUBROUTINES
#
# GAMMA = B**2/A**2 FOR EARTH (B-1)
# GAMMA = 1 FOR MOON (B-1)
#
# CALLING SEQUENCE
# L CALL
# L+1 SETGAMMA
#
# INPUT
# LUNAFLAG=0 FOR EARTH, =1 FOR MOON
#
# OUTPUT
# GAMMA IN GAMRP (B-1)
SETLOC LATLONG1
BANK
COUNT* $$/LT-LG
SETGAMMA DLOAD BOFF # BRANCH FOR EARTH
B2/A2 # EARTH GAMMA
LUNAFLAG
SETGMEX
SLOAD
1B1 # MOON GAMMA
SETGMEX STORE GAMRP
RVQ
GAMRP = 8D
SETLOC LATLONG
BANK
## Page 1242
# ..... SETRE SUBROUTINE .....
# SUBROUTINE TO SET RE (EARTH OR MOON RADIUS)
#
# RE = RM FOR MOON
# RE = RREF FOR FIXED EARTH RADIUS OR COMPUTED RF FOR FISCHER ELLIPSOID
#
# CALLING SEQUENCE
# L CALL
# L+1 SETRE
#
# SUBROUTINES USED
# GETERAD
#
# INPUT
# ERADFLAG = 0 FOR FIXED RE, 1 FOR COMPUTED RE
# ALPHAV +4 = 1/2 SINL IF GETERAD IS CALLED
# LUNAFLAG = 0 FOR EARTH, =1 FOR MOON
#
# OUTPUT
# ERADM = 504RM FOR MOON (METERS B-29)
# ERADM = ERAD OR COMPUTED RF FOR EARTH (METERS B-29)
SETRE STQ DLOAD
SETREX
504RM
BON DLOAD # BRANCH FOR MOON
LUNAFLAG
TSTRLSRM
ERAD
BOFF CALL # ERADFLAG=0 FOR FIXED RE, 1 FOR COMPUTED
ERADFLAG
SETRXX
GETERAD
SETRXX STCALL ERADM # EXIT WITH RE OR RM METERS B-29
SETREX
TSTRLSRM BON VLOAD # ERADFLAG=0, SET R0=RLS
ERADFLAG # =1 R0=RM
SETRXX
RLS
ABVAL SR2R # SCALE FROM B-27 TO B-29
GOTO
SETRXX
SETREX = S2
504RM 2DEC 1738090 B-29 # METERS B-29 (MOON RADIUS)
