Find the nearest point on a line to a specified point, and find 
   the distance between the two points. 

   None. 

   Variable  I/O  Description 
   --------  ---  -------------------------------------------------- 
   linpt, 
   lindir     I   Point on a line and the line's direction vector. 
   point      I   A second point. 
   pnear      O   Nearest point on the line to point. 
   dist       O   Distance between point and pnear. 

   linpt 
   lindir         are, respectively, a point and a direction vector 
                  that define a line in 3-dimensional space.  The 
                  line is the set of points 

                     linpt   +   t * lindir 

                  where t is any real number. 

   point          is a point in 3-dimensional space. 

   pnear          is the nearest point on the input line to the input 
                  point. 

   dist           is the distance between the input line and input 
                  point. 

   None. 

   For every line L and point P, there is a unique closest point 
   on L to P.  Call this closest point C.  It is always true that 
   P - C  is perpendicular to L, and the length of P - C is called 
   the "distance" between P and L. 

   1)  Suppose a line passes through the point ( 1, 2, 3 ) and 
       has direction vector ( 0, 1, 1 ).  We wish to find the 
       closest point on the line to the point ( -6, 9, 10 ).  We 
       can use the code fragment 

          #include "SpiceUsr.h"
               .
               .
               .
          LINPT[0]   =  1.0; 
          LINPT[1]   =  2.0; 
          LINPT[2]   =  3.0; 

          LINDIR[0]  =  0.0; 
          LINDIR[1]  =  1.0; 
          LINDIR[2]  =  1.0; 

          POINT[0]   = -6.0; 
          POINT[1]   =  9.0; 
          POINT[2]   = 10.0; 

          nplnpt_c ( linpt, lindir, point, pnear, &dist );


       After the call, pnear will take the value 

          ( 1., 9., 10. ); 

       dist will be 7.0. 

   None. 

   1)  If the line direction vector lindir is the zero vector, the 
       error SPICE(ZEROVECTOR) is signaled. 

   None. 

   N.J. Bachman   (JPL) 

   None. 

   -CSPICE Version 1.0.0, 16-AUG-1999 (NJB)

   distance between point and line 
   nearest point on line to point