From d54fe7c1f704a63824c5bfa0ece65245572e9b27 Mon Sep 17 00:00:00 2001 From: Joseph Hunkeler Date: Wed, 4 Mar 2015 21:21:30 -0500 Subject: Initial commit --- src/slalib/sun67.htx/node4.html | 131 ++++++++++++++++++++++++++++++++++++++++ 1 file changed, 131 insertions(+) create mode 100644 src/slalib/sun67.htx/node4.html (limited to 'src/slalib/sun67.htx/node4.html') diff --git a/src/slalib/sun67.htx/node4.html b/src/slalib/sun67.htx/node4.html new file mode 100644 index 0000000..81c9586 --- /dev/null +++ b/src/slalib/sun67.htx/node4.html @@ -0,0 +1,131 @@ + + + + +Example Application + + + + + + + + + + + + +
+ +next + +up + +previous +
+ Next: Scope +
+Up: INTRODUCTION +
+ Previous: Purpose +

+

+

+Example Application +

+Here is a simple example of an application program written +using SLALIB calls: +

+         PROGRAM FK4FK5
+   *
+   *  Read a B1950 position from I/O unit 5 and reply on I/O unit 6
+   *  with the J2000 equivalent.  Enter a period to quit.
+   *
+         IMPLICIT NONE
+         CHARACTER C*80,S
+         INTEGER I,J,IHMSF(4),IDMSF(4)
+         DOUBLE PRECISION R4,D4,R5,D5
+         LOGICAL BAD
+
+   *   Loop until a period is entered
+         C = ' '
+         DO WHILE (C(:1).NE.'.')
+
+   *     Read h m s d ' "
+            READ (5,'(A)') C
+            IF (C(:1).NE.'.') THEN
+               BAD = .TRUE.
+
+   *        Decode the RA
+               I = 1
+               CALL sla_DAFIN(C,I,R4,J)
+               IF (J.EQ.0) THEN
+                  R4 = 15D0*R4
+
+   *           Decode the Dec
+                  CALL sla_DAFIN(C,I,D4,J)
+                  IF (J.EQ.0) THEN
+
+   *              FK4 to FK5
+                     CALL sla_FK45Z(R4,D4,1950D0,R5,D5)
+
+   *              Format and output the result
+                     CALL sla_DR2TF(2,R5,S,IHMSF)
+                     CALL sla_DR2AF(1,D5,S,IDMSF)
+                     WRITE (6,
+        :       '(1X,I2.2,2I3.2,''.'',I2.2,2X,A,I2.2,2I3.2,''.'',I1)')
+        :                                                     IHMSF,S,IDMSF
+                     BAD = .FALSE.
+                  END IF
+               END IF
+               IF (BAD) WRITE (6,'(1X,''?'')')
+            END IF
+         END DO
+
+         END
+
+In this example, SLALIB not only provides the complicated FK4 to +FK5 transformation but also +simplifies the tedious and error-prone tasks +of decoding and formatting angles +expressed as hours, minutes etc. The +example incorporates range checking, and avoids the +notorious ``minus zero'' problem (an often-perpetrated bug where +declinations between $0^{\circ}$ and $-1^{\circ}$ lose their minus +sign). +With a little extra elaboration and a few more calls to SLALIB, +defaulting can be provided (enabling unused fields to +be replaced with commas to avoid retyping), proper motions +can be handled, different epochs can be specified, and +so on. See the program COCO (SUN/56) for further ideas. +

+

+ +next + +up + +previous +
+ Next: Scope +
+Up: INTRODUCTION +
+ Previous: Purpose +

+

+

+SLALIB --- Positional Astronomy Library
Starlink User Note 67
P. T. Wallace
12 October 1999
E-mail:ptw@star.rl.ac.uk +
+ + -- cgit