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/node186.html | 144 ++++++++++++++++++++++++++++++++++++++ 1 file changed, 144 insertions(+) create mode 100644 src/slalib/sun67.htx/node186.html (limited to 'src/slalib/sun67.htx/node186.html') diff --git a/src/slalib/sun67.htx/node186.html b/src/slalib/sun67.htx/node186.html new file mode 100644 index 0000000..32d0e60 --- /dev/null +++ b/src/slalib/sun67.htx/node186.html @@ -0,0 +1,144 @@ + + + + +SLA_TPV2C - Plate centre from and x,y,z + + + + + + + + + + + + +
+ +next + +up + +previous +
+ Next: SLA_UE2EL - Universal to Conventional Elements +
+Up: SUBPROGRAM SPECIFICATIONS +
+ Previous: SLA_TPS2C - Plate centre from and +

+

+

    +
+SLA_TPV2C - Plate centre from $\xi,\eta$ and x,y,z +

+
+
ACTION: +
From the tangent plane coordinates of a star of known +direction cosines, determine the direction cosines + of the tangent point (single precision) +

CALL: +
CALL sla_TPV2C (XI, ETA, V, V01, V02, N) +

+

+
GIVEN: +
+
+ + + + + + + + + +
XI,ETARtangent plane coordinates of star (radians)
VR(3)direction cosines of star
+

+
RETURNED: +
+
+ + + + + + + + + + + + + + + + + + + + + + + + + +
V01R(3)direction cosines of tangent point, solution 1
V01R(3)direction cosines of tangent point, solution 2
NInumber of solutions:
0 = no solutions returned (note 2)
1 = only the first solution is useful (note 3)
2 = there are two useful solutions (note 3)
+

+
NOTES: +
+
1. +
The vector V must be of unit length or the result will be wrong. +
2. +
Cases where there is no solution can only arise near the poles. +For example, it is clearly impossible for a star at the pole + itself to have a non-zero XI value. +
3. +
Also near the poles, cases can arise where there are two useful + solutions. The argument N indicates whether the second of the + two solutions returned is useful. + N=1 + indicates only one useful solution, the usual case; under these + circumstances, the second solution can be regarded as valid if + the vector V02 is interpreted as the ``over-the-pole'' case. +
4. +
The projection is called the gnomonic projection; the + Cartesian coordinates $[\,\xi,\eta\,]$ are called + standard coordinates. The latter + are in units of the distance from the tangent plane to the projection + point, i.e. radians near the origin. +
5. +
This routine is the Cartesian equivalent of the routine sla_TPS2C. +
+
+ +next + +up + +previous +
+ Next: SLA_UE2EL - Universal to Conventional Elements +
+Up: SUBPROGRAM SPECIFICATIONS +
+ Previous: SLA_TPS2C - Plate centre from and +

+

+

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