void nplnpt_c ( ConstSpiceDouble linpt [3],
ConstSpiceDouble lindir [3],
ConstSpiceDouble point [3],
SpiceDouble pnear [3],
SpiceDouble * dist )
Find the nearest point on a line to a specified point, and find
the distance between the two points.
None.
GEOMETRY
MATH
VECTOR
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 3dimensional space. The
line is the set of points
linpt + t * lindir
where t is any real number.
point is a point in 3dimensional 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.
1) If the line direction vector lindir is the zero vector, the
error SPICE(ZEROVECTOR) is signaled.
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.
None.
N.J. Bachman (JPL)
CSPICE Version 1.0.0, 16AUG1999 (NJB)
distance between point and line
nearest point on line to point
