dskx02_c |

Table of contents## Proceduredskx02_c ( DSK, ray-surface intercept, type 2 ) void dskx02_c ( SpiceInt handle, ConstSpiceDLADescr * dladsc, ConstSpiceDouble vertex [3], ConstSpiceDouble raydir [3], SpiceInt * plid, SpiceDouble xpt [3], SpiceBoolean * found ) ## AbstractDetermine the plate ID and body-fixed coordinates of the intersection of a specified ray with the surface defined by a type 2 DSK plate model. ## Required_ReadingNone. ## KeywordsGEOMETRY SHAPES ## Brief_I/OVARIABLE I/O DESCRIPTION -------- --- -------------------------------------------------- handle I Handle of DSK kernel containing plate model. dladsc I DLA descriptor of plate model segment. vertex I Ray's vertex in the body fixed frame. raydir I Ray direction in the body fixed frame. plid O ID code of the plate intersected by the ray. xpt O Intercept. found O Flag indicating whether intercept exists. ## Detailed_Inputhandle is the file handle of a DSK file containing a shape model for a target body. The shape model is stored in a type 2 DSK segment. dladsc is the DLA descriptor of a type 2 DSK segment containing plate model data representing the surface of the target body. Normally this descriptor will be obtained by a search through a DSK file using the DLA search routines; see the -Examples header section below for a working code example illustrating a simple search. vertex is the vertex of a ray. `vertex' is expressed relative to the body fixed reference frame associated with the target body. This reference frame is the same frame relative to which the vertices of the plate model are expressed. Units are km. The vertex is required to be outside the target body. raydir is the ray's direction vector. `raydir' is expressed relative to the body fixed reference frame associated with the target body. ## Detailed_Outputplid is the ID of the plate closest to the input ray's vertex at which a ray-surface intercept exists. If no intercept exists, `plid' is undefined. xpt is the ray-target intercept closest to the ray's vertex, if an intercept exists. `xpt' is expressed relative to the body-fixed reference frame associated with the target body. Units are km. If no intercept exists, `xpt' is undefined. found is a logical flag that indicates whether or not the ray does indeed intersect the target. If the ray intersects a plate `found' is SPICETRUE. Otherwise `found' is SPICEFALSE. ## ParametersSee the header file SpiceDtl.h for the values of tolerance parameters used by default by the ray-surface intercept algorithm. See the header file SpiceDLA.h for declarations of DLA descriptor sizes and documentation of the contents of DLA descriptors. See the header file SpiceDSK.h for declarations of DSK descriptor sizes and documentation of the contents of DSK descriptors. See the header file SpiceDSK.h for declarations of DSK data type 2 (plate model) parameters. ## Exceptions1) If the input handle is invalid, an error is signaled by a routine in the call tree of this routine. 2) If a file read error occurs, the error is signaled by a routine in the call tree of this routine. 3) If the input DLA descriptor is invalid, the effect of this routine is undefined. The error *may* be diagnosed by routines in the call tree of this routine, but there are no guarantees. 4) If an error occurs while trying to look up any component of the shape model, the error is signaled by a routine in the call tree of this routine. 5) If the input ray direction is the zero vector, the error SPICE(ZEROVECTOR) is signaled by a routine in the call tree of this routine. 6) If the coarse voxel grid scale of the shape model is less than 1, the error SPICE(VALUEOUTOFRANGE) is signaled by a routine in the call tree of this routine. 7) If the coarse voxel grid of the shape model contains more than SPICE_DSK_MAXCGR (see SpiceDSK.h) voxels, the error SPICE(GRIDTOOLARGE) is signaled by a routine in the call tree of this routine. 8) If the plate list for any intersected voxel is too large for this routine to buffer, the error SPICE(ARRAYTOOSMALL) is signaled by a routine in the call tree of this routine. 9) Due to round-off errors, results from this routine may differ across platforms. Results also may differ from those expected---and not necessarily by a small amount. For example, a ray may miss a plate it was expected to hit and instead hit another plate considerably farther from the ray's vertex, or miss the target entirely. 10) In the event that an intercept point lies on multiple plates (that is, the point is on an edge or vertex), a plate will be selected. Due to round-off error, the selection may vary across platforms. ## FilesSee the description of the input argument `handle'. ## ParticularsThis routine solves the ray-surface intercept problem for a specified ray and a surface represented by triangular plate model. The surface representation is provided by data in a type 2 segment of a DSK file. This routine does not assume that the segment from which the surface model data are read represents the entire surface of the target body. A program could call this routine repeatedly to find the surface intercept of a ray and a shape model partitioned into multiple segments. In general, this routine should be expected to run faster when used with smaller shape models. ## 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 surface intercept points corresponding to a latitude/ longitude grid of a specified resolution, for a specified target body. This simple program assumes the shape model for the target body is stored in a single type 2 DSK segment, and that this segment is the first one in the DSK file to which it belongs. Example code begins here. /. Program dskx02_ex1 ./ #include <stdio.h> #include <math.h> #include "SpiceUsr.h" int main() { /. Local parameters ./ #define FILSIZ 256 #define NLAT 9 #define NLON 9 #define TOL ( 1.e-12 ) #define SPICE_MXCOR3_IDX 21 /. Local variables ./ SpiceBoolean found; SpiceChar dsk [ FILSIZ ]; SpiceDLADescr dladsc; SpiceDSKDescr dskdsc; SpiceDouble lat; SpiceDouble lon; SpiceDouble maxr; SpiceDouble r; SpiceDouble raydir [3]; SpiceDouble vertex [3]; SpiceDouble xlat; SpiceDouble xlon; SpiceDouble xpt [3]; SpiceDouble xr; SpiceInt handle; SpiceInt i; SpiceInt j; SpiceInt plid; /. Prompt for the name of the DSK to read. ./ prompt_c ( "Enter DSK name > ", FILSIZ, dsk ); /. Open the DSK file for read access. We use the DAS-level interface for this function. ./ dasopr_c ( dsk, &handle ); /. Begin a forward search through the kernel, treating the file as a DLA. In this example, it's a very short search. ./ dlabfs_c ( handle, &dladsc, &found ); if ( !found ) { /. We arrive here only if the kernel contains no segments. This is unexpected, but we're prepared for it. ./ setmsg_c ( "No segments found in DSK file #."); errch_c ( "#", dsk ); sigerr_c ( "SPICE(NODATA)" ); } /. If we made it this far, DLADSC is the DLA descriptor of the first segment. We're going to generate the intercept points using a set of rays which point toward the origin and whose vertices are on a specified specified lat/lon grid. To start out we must pick a reasonable range from the origin for the vertices: the range must be large enough so that the vertices are guaranteed to be outside the target body but small enough that we don't lose too much precision in the surface intercept computation. We'll look up the upper bound for the target radius, then use 2 times this value as the vertex magnitude. ./ dskgd_c ( handle, &dladsc, &dskdsc ); maxr = dskdsc.co3max; r = 2.0 * maxr; /. Now generate the intercept points. We generate intercepts along latitude bounds, working from north to south. Latitude ranges from +80 to -80 degrees. Longitude ranges from 0 to 320 degrees. The increment is 20 degrees for latitude and 40 degrees for longitude. ./ for ( i = 0; i < NLAT; i++ ) { lat = rpd_c() * ( 80.0 - 20.0*i ); for ( j = 0; j < NLON; j++ ) { lon = rpd_c() * 40.0*j; /. Produce a ray vertex for the current lat/lon value. Negate the vertex to produce the ray's direction vector. ./ latrec_c ( r, lon, lat, vertex ); vminus_c ( vertex, raydir ); /. Find the surface intercept for this ray. ./ ## RestrictionsNone. ## Literature_References[1] A. Woo, "Fast Ray-Box Intersection", Graphic Gems I, 395-396, Aug. 1990 ## Author_and_InstitutionN.J. Bachman (JPL) J.A. Bytof (JPL) J. Diaz del Rio (ODC Space) W.L. Taber (JPL) E.D. Wright (JPL) ## Version-CSPICE Version 1.0.3, 07-AUG-2021 (JDR) Edited the header to comply with NAIF standard. Updated code example to remove unnecessary include files. -CSPICE Version 1.0.2, 04-APR-2017 (EDW) Edit to example program to use "%d" with explicit casts to int for printing SpiceInts with printf. -CSPICE Version 1.0.1, 20-JUL-2011 (NJB) Header correction: the detailed input section now says that the ray's vertex *is* required to be outside the target body. -CSPICE Version 1.0.0, 05-JUN-2010 (NJB) (EDW) (JAB) (WLT) ## Index_Entriesplate and plate model point intersected by ray intersection of ray and surface |

Fri Dec 31 18:41:05 2021