vprjp_c |

Table of contents## Procedurevprjp_c ( Vector projection onto plane ) void vprjp_c ( ConstSpiceDouble vin [3], ConstSpicePlane * plane, SpiceDouble vout [3] ) ## AbstractProject a vector onto a specified plane, orthogonally. ## Required_ReadingPLANES ## KeywordsGEOMETRY MATH PLANE VECTOR ## Brief_I/OVARIABLE I/O DESCRIPTION -------- --- -------------------------------------------------- vin I Vector to be projected. plane I A SPICE plane onto which `vin' is projected. vout O Vector resulting from projection. ## Detailed_Inputvin is a 3-vector that is to be orthogonally projected onto a specified plane. plane is a SPICE plane that represents the geometric plane onto which `vin' is to be projected. The normal vector component of a SPICE plane has unit length. ## Detailed_Outputvout is the vector resulting from the orthogonal projection of `vin' onto `plane'. `vout' is the closest point in the specified plane to `vin'. ## ParametersNone. ## Exceptions1) If the normal vector of the input plane does not have unit length (allowing for round-off error), the error SPICE(NONUNITNORMAL) is signaled by a routine in the call tree of this routine. ## FilesNone. ## ParticularsProjecting a vector `vin' orthogonally onto a plane can be thought of as finding the closest vector in the plane to `vin'. This "closest vector" always exists; it may be coincident with the original vector. Two related routines are vprjpi_c, which inverts an orthogonal projection of a vector onto a plane, and vproj_c, which projects a vector orthogonally onto another vector. ## ExamplesThe numerical results shown for this example may differ across platforms. The results depend on the SPICE kernels used as input, the compiler and supporting libraries, and the machine specific arithmetic implementation. 1) Find the closest point in the ring plane of a planet to a spacecraft located at a point (in body-fixed coordinates). Example code begins here. /. Program vprjp_ex1 ./ #include <stdio.h> #include "SpiceUsr.h" int main( ) { /. Local variables. ./ SpiceDouble proj [3]; SpicePlane ringpl; /. Set the spacecraft location and define the normal vector as the normal to the equatorial plane, and the origin at the body/ring center. ./ SpiceDouble scpos [3] = { -29703.16955, 879765.72163, -137280.21757 }; SpiceDouble norm [3] = { 0.0, 0.0, 1.0 }; SpiceDouble orig [3] = { 0.0, 0.0, 0.0 }; /. Create the plane structure. ./ nvp2pl_c ( norm, orig, &ringpl ); /. Project the position vector onto the ring plane. ./ ## Restrictions1) It is recommended that the input plane be created by one of the CSPICE routines nvc2pl_c ( Normal vector and constant to plane ) nvp2pl_c ( Normal vector and point to plane ) psv2pl_c ( Point and spanning vectors to plane ) In any case the input plane must have a unit length normal vector and a plane constant consistent with the normal vector. ## Literature_References[1] G. Thomas and R. Finney, "Calculus and Analytic Geometry," 7th Edition, Addison Wesley, 1988. ## Author_and_InstitutionN.J. Bachman (JPL) J. Diaz del Rio (ODC Space) B.V. Semenov (JPL) ## Version-CSPICE Version 1.0.2, 24-AUG-2021 (JDR) (NJB) Edited the header to comply with NAIF standard. Added complete code example. Added entry #1 to -Exceptions section, and entry #1 to -Restrictions. -CSPICE Version 1.0.1, 01-FEB-2017 (BVS) Typo fix: pnv2pl_c -> nvp2pl_c. -CSPICE Version 1.0.0, 05-MAR-1999 (NJB) ## Index_Entriesvector projection onto plane |

Fri Dec 31 18:41:15 2021