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<H2><A NAME="SECTION0004170000000000000000">SLA_TP2S - Tangent Plane to Spherical</A>
<A NAME="xref_SLA_TP2S"> </A><A NAME="SLA_TP2S"> </A>
</H2>
<DL>
<DT><STRONG>ACTION:</STRONG>
<DD>Transform tangent plane coordinates into spherical
coordinates (single precision)
<P> <DT><STRONG>CALL:</STRONG>
<DD><TT>CALL sla_TP2S (XI, ETA, RAZ, DECZ, RA, DEC)</TT>
<P> </DL>
<P> <DL>
<DT><STRONG>GIVEN:</STRONG>
<DD>
<BR>
<TABLE CELLPADDING=3>
<TR VALIGN="TOP"><TD ALIGN="LEFT"><EM>XI,ETA</EM></TD>
<TH ALIGN="LEFT"><B>R</B></TH>
<TD ALIGN="LEFT" NOWRAP>tangent plane rectangular coordinates (radians)</TD>
</TR>
<TR VALIGN="TOP"><TD ALIGN="LEFT"><EM>RAZ,DECZ</EM></TD>
<TD ALIGN="LEFT"><B>R</B></TD>
<TD ALIGN="LEFT" NOWRAP>spherical coordinates of tangent point (radians)</TD>
</TR>
</TABLE></DL>
<P> <DL>
<DT><STRONG>RETURNED:</STRONG>
<DD>
<BR>
<TABLE CELLPADDING=3>
<TR VALIGN="TOP"><TD ALIGN="LEFT"><EM>RA,DEC</EM></TD>
<TH ALIGN="LEFT"><B>R</B></TH>
<TD ALIGN="LEFT" NOWRAP>spherical coordinates (radians)</TD>
</TR>
</TABLE></DL>
<P> <DL>
<DT><STRONG>NOTES:</STRONG>
<DD><DL COMPACT>
<DT>1.
<DD>The projection is called the <I>gnomonic</I> projection; the
Cartesian coordinates <IMG WIDTH="41" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img85.gif"
ALT="$[\,\xi,\eta\,]$"> are called
<I>standard coordinates.</I> The latter
are in units of the distance from the tangent plane to the projection
point, <I>i.e.</I> radians near the origin.
<DT>2.
<DD>When working in <IMG WIDTH="58" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img50.gif"
ALT="$[\,x,y,z\,]$"> rather than spherical coordinates, the
equivalent Cartesian routine sla_TP2V is available.
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<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>
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