Direction Cosines to Tangent Plane
CALL sla_DV2TP (V, V0, XI, ETA, J)
V  D(3)  direction cosines of star 


V0  D(3)  direction cosines of tangent point 
XI,ETA  D  tangent plane coordinates (radians) 
 
J  I  status: 
 

 0 = OK, star on tangent plane 



 1 = error, star too far from axis 



 2 = error, antistar on tangent plane 



 3 = error, antistar too far from axis 