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void palDs2tp
(
double
ra
,
double
dec
,
double
raz
,
double
decz
,
double *
xi
,
double *
eta
,
int *
j
)
Definition at line
83
of file
palDs2tp.c
.
Referenced by
t_tp()
.
84
{
85
86
const
double
TINY = 1.0e-6;
87
88
double
cdec;
89
double
sdec;
90
double
radif;
91
double
cdecz;
92
double
denom;
93
double
sdecz;
94
double
cradif;
95
double
sradif;
96
97
/* Trig functions */
98
sdecz = sin(decz);
99
sdec = sin(dec);
100
cdecz = cos(decz);
101
cdec = cos(dec);
102
radif = ra - raz;
103
sradif = sin(radif);
104
cradif = cos(radif);
105
106
/* Reciprocal of star vector length to tangent plane */
107
denom = sdec * sdecz + cdec * cdecz * cradif;
108
109
/* Handle vectors too far from axis */
110
if
(denom > TINY) {
111
*j = 0;
112
}
else
if
(denom >= 0.) {
113
*j = 1;
114
denom = TINY;
115
}
else
if
(denom > -TINY) {
116
*j = 2;
117
denom = -TINY;
118
}
else
{
119
*j = 3;
120
}
121
122
/* Compute tangent plane coordinates (even in dubious cases) */
123
*xi = cdec * sradif / denom;
124
*eta = (sdec * cdecz - cdec * sdecz * cradif) / denom;
125
126
return
;
127
}
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pal
pal.h
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