nplnpt_c |
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Procedurenplnpt_c ( Nearest point on line to point ) void nplnpt_c ( ConstSpiceDouble linpt [3], ConstSpiceDouble lindir [3], ConstSpiceDouble point [3], SpiceDouble pnear [3], SpiceDouble * dist ) AbstractFind the nearest point on a line to a specified point, and find the distance between the two points. Required_ReadingNone. KeywordsGEOMETRY MATH VECTOR Brief_I/OVARIABLE 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_Inputlinpt, 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_Outputpnear is the nearest point on the input line to the input point. dist is the distance between the input line and input point. ParametersNone. Exceptions1) If the line direction vector `lindir' is the zero vector, the error SPICE(ZEROVECTOR) is signaled. FilesNone. ParticularsFor 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. Examples1) 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. RestrictionsNone. Literature_ReferencesNone. Author_and_InstitutionN.J. Bachman (JPL) J. Diaz del Rio (ODC Space) Version-CSPICE Version 1.0.1, 04-AUG-2021 (JDR) Edited the header to comply with NAIF standard. -CSPICE Version 1.0.0, 16-AUG-1999 (NJB) Index_Entriesdistance between point and line nearest point on line to point |
Fri Dec 31 18:41:10 2021