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nplnpt_c
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Procedure
Abstract
Required_Reading
Keywords
Brief_I/O
Detailed_Input
Detailed_Output
Parameters
Exceptions
Files
Particulars
Examples
Restrictions
Literature_References
Author_and_Institution
Version
Index_Entries

Procedure

   void nplnpt_c ( ConstSpiceDouble    linpt  [3],
                   ConstSpiceDouble    lindir [3],
                   ConstSpiceDouble    point  [3],
                   SpiceDouble         pnear  [3],
                   SpiceDouble       * dist       ) 

Abstract

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

Required_Reading

 
   None. 
 

Keywords

 
   GEOMETRY 
   MATH 
   VECTOR 
 

Brief_I/O

 
   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. 
 

Detailed_Input

 
   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. 
 

Detailed_Output

 
   pnear          is the nearest point on the input line to the input 
                  point. 
 
   dist           is the distance between the input line and input 
                  point. 
 

Parameters

 
   None. 
 

Exceptions

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

Files

 
   None. 
 

Particulars

 
   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. 
 

Examples

 
   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. 
 

Restrictions

 
   None. 
 

Literature_References

 
   None. 
 

Author_and_Institution

 
   N.J. Bachman   (JPL) 
 

Version

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

Index_Entries

 
   distance between point and line 
   nearest point on line to point 
 
Wed Apr  5 17:54:39 2017