void dskn02_c ( SpiceInt handle,
ConstSpiceDLADescr * dladsc,
SpiceInt plid,
SpiceDouble normal[3] )
Compute the unit normal vector for a specified plate from a type
2 DSK segment.
DAS
DSK
DAS
DSK
FILES
Variable I/O Description
-------- --- --------------------------------------------------
handle I DSK file handle.
dladsc I DLA descriptor.
plid I Plate ID.
normal O Plate's unit normal vector.
handle is the handle of a DSK file containing a type 2
segment from which data are to be fetched.
dladsc is the DLA descriptor associated with the segment
from which data are to be fetched.
plid is the plate ID. Plate IDs range from 1 to NP
(the number of plates in the segment identified
by `dladsc').
normal is the normal vector associated with the plate
designated by `plid'. The direction of `normal' is
determined by the order of the plate's vertices;
the vertices are presumed to be ordered in the
right-handed (counterclockwise) sense about the
normal direction. If the plate's vertices are
v1, v2, v3, then `normal' points in the direction
(v2 - v1) x ( v3 - v2 )
where "x" represents the cross product operator.
The vector `normal' is expressed in the body-fixed
reference frame of the segment designated by
`dladsc'. The center of this frame is the origin of
the cartesian coordinate system in which the vertices
are expressed. Note that the frame center need not
coincide with the central body of the segment. Units
are km.
The vector has magnitude 1.
If an error occurs on the call, `normal' is
undefined.
See the header file
SpiceDLA.h
1) If the input handle is invalid, the error will be diagnosed by
routines in the call tree of this routine.
2) If a file read error occurs, the error will be diagnosed by
routines 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 `plid' is less than 1 or greater than the number of plates
in the segment, the error SPICE(INDEXOUTOFRANGE) is signaled.
5) This routine does not check for linear independence of the
plate's edges. The plate model is assumed to be geometrically
valid.
See input argument `handle'.
None.
1) Look up all the vertices associated with each plate
of the model contained in a specified type 2 segment. For each
plate, display the plate's vertices and normal vector.
For this example, we'll show the context of this look-up:
opening the DSK file for read access, traversing a trivial,
one-segment list to obtain the segment of interest.
Example code begins here.
#include <stdio.h>
#include "SpiceUsr.h"
#include "SpiceDLA.h"
#include "dsk_proto.h"
int main()
{
/.
Constants
./
#define PBUFSIZ 10000
#define FILSIZ 256
/.
Local variables
./
SpiceBoolean found;
SpiceChar dsk [ FILSIZ ];
SpiceDLADescr dladsc;
SpiceDouble normal [3];
SpiceDouble verts [3][3];
SpiceInt handle;
SpiceInt i;
SpiceInt j;
SpiceInt n;
SpiceInt np;
SpiceInt nread;
SpiceInt nv;
SpiceInt nvtx;
SpiceInt plates[PBUFSIZ][3];
SpiceInt plix;
SpiceInt remain;
SpiceInt start;
/.
Prompt for name of DSK and open file for reading.
./
prompt_c ( "Enter DSK name > ", FILSIZ, dsk );
dasopr_c ( dsk, &handle );
dlabfs_c ( handle, &dladsc, &found );
if ( !found )
{
setmsg_c ( "No segment found in file #." );
errch_c ( "#", dsk );
sigerr_c ( "SPICE(NOSEGMENT)" );
}
/.
Get segment vertex and plate counts.
./
dskz02_c ( handle, &dladsc, &nv, &np );
printf ( "\n"
"Number of vertices: %d\n"
"Number of plates: %d\n",
(int)nv,
(int)np );
/.
Display the vertices of each plate.
./
remain = np;
start = 1;
while ( remain > 0 )
{
/.
`nread' is the number of plates we"ll read on this
loop pass.
./
nread = mini_c ( 2, PBUFSIZ, remain );
dskp02_c ( handle, &dladsc, start, nread, &n, plates );
for ( i = 0; i < nread; i++ )
{
plix = start + i;
/.
Read the vertices of the current plate.
./
for ( j = 0; j < 3; j++ )
{
dskv02_c ( handle, &dladsc, plates[i][j],
1, &nvtx,
( SpiceDouble(*)[3] )(verts[j]) );
}
/.
Display the vertices of the current plate:
./
printf ( "\n"
" Plate number: %d\n"
" Vertex 1: ( %16.8e %16.8e %16.8e )\n"
" Vertex 2: ( %16.8e %16.8e %16.8e )\n"
" Vertex 3: ( %16.8e %16.8e %16.8e )\n",
(int)plix,
verts[0][0], verts[0][1], verts[0][2],
verts[1][0], verts[1][1], verts[1][2],
verts[2][0], verts[2][1], verts[2][2] );
/.
Display the normal vector of the current plate:
./
dskn02_c ( handle, &dladsc, plix, normal );
printf( " Normal: ( %16.8e %16.8e %16.8e )\n",
normal[0], normal[1], normal[2] );
}
start = start + nread;
remain = remain - nread;
}
/.
Close the kernel. This isn't necessary in a stand-
alone program, but it's good practice in subroutines
because it frees program and system resources.
./
dascls_c ( handle );
return ( 0 );
}
When this program was executed on a PC/Linux/gcc/32bit
platform, using a DSK file representing a regular icosahedron,
the output was:
Number of vertices: 12
Number of plates: 20
Plate number: 1
Vertex 1: ( 0.00000000e+00 0.00000000e+00 1.17557000e+00 )
Vertex 2: ( 1.05146000e+00 0.00000000e+00 5.25731000e-01 )
Vertex 3: ( 3.24920000e-01 1.00000000e+00 5.25731000e-01 )
Normal: ( 4.91124160e-01 3.56821347e-01 7.94654382e-01 )
Plate number: 2
Vertex 1: ( 0.00000000e+00 0.00000000e+00 1.17557000e+00 )
Vertex 2: ( 3.24920000e-01 1.00000000e+00 5.25731000e-01 )
Vertex 3: ( -8.50651000e-01 6.18034000e-01 5.25731000e-01 )
Normal: ( -1.87592328e-01 5.77350079e-01 7.94654645e-01 )
...
Plate number: 20
Vertex 1: ( 8.50651000e-01 -6.18034000e-01 -5.25731000e-01 )
Vertex 2: ( 0.00000000e+00 0.00000000e+00 -1.17557000e+00 )
Vertex 3: ( 8.50651000e-01 6.18034000e-01 -5.25731000e-01 )
Normal: ( 6.07061680e-01 0.00000000e+00 -7.94654715e-01 )
See Exceptions.
None.
N.J. Bachman (JPL)
-CSPICE Version 1.0.1, 27-JAN-2016 (NJB)
Edit to example program to use "%d" with explicit casts
to int for printing SpiceInts with printf.
Updated header Detailed_Output and Index_Entries
sections.
-CSPICE Version 1.0.0, 03-JUN-2010 (NJB)
compute normal vector for a type 2 dsk plate
compute normal vector from dsk type 2 plate id
Link to routine dskn02_c source file dskn02_c.c
|