1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
|
DOUBLE PRECISION FUNCTION sla_ZD (HA, DEC, PHI)
*+
* - - -
* Z D
* - - -
*
* HA, Dec to Zenith Distance (double precision)
*
* Given:
* HA d Hour Angle in radians
* DEC d declination in radians
* PHI d observatory latitude in radians
*
* The result is in the range 0 to pi.
*
* Notes:
*
* 1) The latitude must be geodetic. In critical applications,
* corrections for polar motion should be applied.
*
* 2) In some applications it will be important to specify the
* correct type of hour angle and declination in order to
* produce the required type of zenith distance. In particular,
* it may be important to distinguish between the zenith distance
* as affected by refraction, which would require the "observed"
* HA,Dec, and the zenith distance in vacuo, which would require
* the "topocentric" HA,Dec. If the effects of diurnal aberration
* can be neglected, the "apparent" HA,Dec may be used instead of
* the topocentric HA,Dec.
*
* 3) No range checking of arguments is done.
*
* 4) In applications which involve many zenith distance calculations,
* rather than calling the present routine it will be more efficient
* to use inline code, having previously computed fixed terms such
* as sine and cosine of latitude, and perhaps sine and cosine of
* declination.
*
* P.T.Wallace Starlink 3 April 1994
*
* Copyright (C) 1995 Rutherford Appleton Laboratory
*-
IMPLICIT NONE
DOUBLE PRECISION HA,DEC,PHI
DOUBLE PRECISION SH,CH,SD,CD,SP,CP,X,Y,Z
SH=SIN(HA)
CH=COS(HA)
SD=SIN(DEC)
CD=COS(DEC)
SP=SIN(PHI)
CP=COS(PHI)
X=CH*CD*SP-SD*CP
Y=SH*CD
Z=CH*CD*CP+SD*SP
sla_ZD=ATAN2(SQRT(X*X+Y*Y),Z)
END
|
