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
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
|
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN">
<!--Converted with LaTeX2HTML 97.1 (release) (July 13th, 1997)
by Nikos Drakos (nikos@cbl.leeds.ac.uk), CBLU, University of Leeds
* revised and updated by: Marcus Hennecke, Ross Moore, Herb Swan
* with significant contributions from:
Jens Lippman, Marek Rouchal, Martin Wilck and others -->
<HTML>
<HEAD>
<TITLE>Formatting angles</TITLE>
<META NAME="description" CONTENT="Formatting angles">
<META NAME="keywords" CONTENT="sun67">
<META NAME="resource-type" CONTENT="document">
<META NAME="distribution" CONTENT="global">
<META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=iso_8859_1">
<LINK REL="STYLESHEET" HREF="sun67.css">
<LINK REL="previous" HREF="node198.html">
<LINK REL="up" HREF="node198.html">
<LINK REL="next" HREF="node200.html">
</HEAD>
<BODY >
<BR> <HR>
<A NAME="tex2html2443" HREF="node200.html">
<IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next" SRC="next_motif.gif"></A>
<A NAME="tex2html2441" HREF="node198.html">
<IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up" SRC="up_motif.gif"></A>
<A NAME="tex2html2437" HREF="node198.html">
<IMG WIDTH="63" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="previous" SRC="previous_motif.gif"></A> <A HREF="sun67.html#stardoccontents"><IMG ALIGN="BOTTOM" BORDER="0"
SRC="contents_motif.gif"></A>
<BR>
<B> Next:</B> <A NAME="tex2html2444" HREF="node200.html">Vectors and Matrices</A>
<BR>
<B>Up:</B> <A NAME="tex2html2442" HREF="node198.html">Spherical Trigonometry</A>
<BR>
<B> Previous:</B> <A NAME="tex2html2438" HREF="node198.html">Spherical Trigonometry</A>
<BR> <HR> <P>
<P><!--End of Navigation Panel-->
<H3><A NAME="SECTION00051100000000000000">
Formatting angles</A>
</H3>
SLALIB has routines for decoding decimal numbers
from character form and for converting angles to and from
sexagesimal form (hours, minutes, seconds or degrees,
arcminutes, arcseconds). These apparently straightforward
operations contain hidden traps which the SLALIB routines
avoid.
<P>
There are five routines for decoding numbers from a character
string, such as might be entered using a keyboard.
They all work in the same style, and successive calls
can work their way along a single string decoding
a sequence of numbers of assorted types. Number
fields can be separated by spaces or commas, and can be defaulted
to previous values or to preset defaults.
<P>
Three of the routines decode single numbers:
sla_INTIN
(integer),
sla_FLOTIN
(single precision floating point) and
sla_DFLTIN
(double precision). A minus sign can be
detected even when the number is zero; this avoids
the frequently-encountered ``minus zero'' bug, where
declinations <I>etc.</I> in
the range <IMG WIDTH="18" HEIGHT="14" ALIGN="BOTTOM" BORDER="0"
SRC="img1.gif"
ALT="$0^{\circ}$"> to <IMG WIDTH="30" HEIGHT="27" ALIGN="MIDDLE" BORDER="0"
SRC="img2.gif"
ALT="$-1^{\circ}$"> mysteriously migrate to
the range <IMG WIDTH="18" HEIGHT="14" ALIGN="BOTTOM" BORDER="0"
SRC="img1.gif"
ALT="$0^{\circ}$"> to <IMG WIDTH="30" HEIGHT="27" ALIGN="MIDDLE" BORDER="0"
SRC="img236.gif"
ALT="$+1^{\circ}$">.Here is an example (in Fortran) where we wish to
read two numbers, and integer <TT>IX</TT> and a real, <TT>Y</TT>,
with <TT>X</TT> defaulting to zero and <TT>Y</TT> defaulting to
<TT>X</TT>:
<P><PRE>
DOUBLE PRECISION Y
CHARACTER*80 A
INTEGER IX,I,J
* Input the string to be decoded
READ (*,'(A)') A
* Preset IX to its default value
IX = 0
* Point to the start of the string
I = 1
* Decode an integer
CALL sla_INTIN(A,I,IX,J)
IF (J.GT.1) GO TO ... (bad IX)
* Preset Y to its default value
Y = DBLE(IX)
* Decode a double precision number
CALL sla_DFLTIN(A,I,Y,J)
IF (J.GT.1) GO TO ... (bad Y)
</PRE>
<P>
Two additional routines decode a 3-field sexagesimal number:
sla_AFIN
(degrees, arcminutes, arcseconds to single
precision radians) and
sla_DAFIN
(the same but double precision). They also
work using other units such as hours <I>etc</I>. if
you multiply the result by the appropriate factor. An example
Fortran program which uses
sla_DAFIN
was given earlier, in section 1.2.
<P>
SLALIB provides four routines for expressing an angle in radians
in a preferred range. The function
sla_RANGE
expresses an angle
in the range <IMG WIDTH="25" HEIGHT="25" ALIGN="MIDDLE" BORDER="0"
SRC="img47.gif"
ALT="$\pm \pi$">;sla_RANORM
expresses an angle in the range
<IMG WIDTH="48" HEIGHT="25" ALIGN="MIDDLE" BORDER="0"
SRC="img143.gif"
ALT="$0-2\pi$">. The functions
sla_DRANGE
and
sla_DRANRM
are double precision versions.
<P>
Several routines
(sla_CTF2D,
sla_CR2AF
<I>etc.</I>) are provided to convert
angles to and from
sexagesimal form (hours, minute, seconds or degrees,
arcminutes and arcseconds).
They avoid the common
``converting from integer to real at the wrong time''
bug, which produces angles like <IMG WIDTH="113" HEIGHT="17" ALIGN="BOTTOM" BORDER="0"
SRC="img237.gif"
ALT="$24^{h}\,59^{m}\,59^{s}.999$">.Here is a program which displays an hour angle
stored in radians:
<P><PRE>
DOUBLE PRECISION HA
CHARACTER SIGN
INTEGER IHMSF(4)
:
CALL sla_DR2TF(3,HA,SIGN,IHMSF)
WRITE (*,'(1X,A,3I3.2,''.'',I3.3)') SIGN,IHMSF
</PRE>
<P>
<BR> <HR>
<A NAME="tex2html2443" HREF="node200.html">
<IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next" SRC="next_motif.gif"></A>
<A NAME="tex2html2441" HREF="node198.html">
<IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up" SRC="up_motif.gif"></A>
<A NAME="tex2html2437" HREF="node198.html">
<IMG WIDTH="63" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="previous" SRC="previous_motif.gif"></A> <A HREF="sun67.html#stardoccontents"><IMG ALIGN="BOTTOM" BORDER="0"
SRC="contents_motif.gif"></A>
<BR>
<B> Next:</B> <A NAME="tex2html2444" HREF="node200.html">Vectors and Matrices</A>
<BR>
<B>Up:</B> <A NAME="tex2html2442" HREF="node198.html">Spherical Trigonometry</A>
<BR>
<B> Previous:</B> <A NAME="tex2html2438" HREF="node198.html">Spherical Trigonometry</A>
<BR> <HR> <P>
<P><!--End of Navigation Panel-->
<ADDRESS>
<I>SLALIB --- Positional Astronomy Library<BR>Starlink User Note 67<BR>P. T. Wallace<BR>12 October 1999<BR>E-mail:ptw@star.rl.ac.uk</I>
</ADDRESS>
</BODY>
</HTML>
|
