Table of contents
CSPICE_PLTEXP expands a triangular plate by a specified amount.
The expanded plate is co-planar with, and has the same orientation as,
the original. The centroids of the two plates coincide.
Given:
iverts an array containing three vertices of a triangular
plate.
[3,3] = size(iverts); double = class(iverts)
Each vertex is a three-dimensional vector. The elements
iverts(j,i), j = 1 ... 3
are, respectively, the X, Y, and Z components of the
ith vertex.
delta a fraction by which the plate is to be scaled.
[1,1] = size(delta); double = class(delta)
Scaling is done so that the scaled plate has the following
properties:
- it is co-planar with the input plate
- its centroid coincides with that of the input
plate
- its sides remain parallel to the corresponding
sides of the input plate
- the distance of each vertex from the centroid is
(1+delta) times the corresponding distance for
the input plate
the call:
[overts] = cspice_pltexp( iverts, delta )
returns:
overts an array containing three vertices of the triangular
plate resulting from scaling the input plate.
[3,3] = size(overts); double = class(overts)
If `ctroid' is the centroid (the average of the vertices)
of the input plate, then the jth vertex of `overts'
overts(j,i), j = 1 ... 3
is equal to
ctroid(j) + (1+delta)*( iverts(j,i) - ctroid(j) ),
j = 1 ... 3
None.
Any numerical results shown for this example may differ between
platforms as the results depend on the SPICE kernels used as input
and the machine specific arithmetic implementation.
1) Expand an equilateral triangle that lies in the plane
{ (x,y,z) : z = 7 }
Use an expansion fraction of 1.0; this doubles the size of
the plate.
Example code begins here.
function pltexp_ex1()
s = sqrt( 3.0 ) / 2.0;
iverts = [ [ s; -0.5; 7.0] [ 0.0; 1.0; 7.0] [ -s; -0.5; 7.0] ];
delta = 1.0;
overts = cspice_pltexp ( iverts, delta );
fprintf ( '\nVertices of input plate: \n')
fprintf ( ' I1 = %20.12f %20.12f %20.12f\n', iverts(:,1) )
fprintf ( ' I2 = %20.12f %20.12f %20.12f\n', iverts(:,2) )
fprintf ( ' I3 = %20.12f %20.12f %20.12f\n', iverts(:,3) )
fprintf ( '\nVertices of output plate: \n')
fprintf ( ' O1 = %20.12f %20.12f %20.12f\n', overts(:,1) )
fprintf ( ' O2 = %20.12f %20.12f %20.12f\n', overts(:,2) )
fprintf ( ' O3 = %20.12f %20.12f %20.12f\n', overts(:,3) )
When this program was executed on a Mac/Intel/Octave5.x/64-bit
platform, the output was:
Vertices of input plate:
I1 = 0.866025403784 -0.500000000000 7.000000000000
I2 = 0.000000000000 1.000000000000 7.000000000000
I3 = -0.866025403784 -0.500000000000 7.000000000000
Vertices of output plate:
O1 = 1.732050807569 -1.000000000000 7.000000000000
O2 = 0.000000000000 2.000000000000 7.000000000000
O3 = -1.732050807569 -1.000000000000 7.000000000000
This routine supports "greedy" ray-plate intercept algorithms.
Such algorithms attempt to ensure that false negatives---in which
an intersection is not found due to round-off error---do not
occur. In such an algorithm, the plate of interest is expanded
slightly before the intersection test is performed.
1) If any of the input arguments, `iverts' or `delta', is
undefined, an error is signaled by the Matlab error handling
system.
2) If any of the input arguments, `iverts' or `delta', is not of
the expected type, or it does not have the expected dimensions
and size, an error is signaled by the Mice interface.
None.
None.
DSK.REQ
MICE.REQ
None.
J. Diaz del Rio (ODC Space)
E.D. Wright (JPL)
-Mice Version 1.1.0, 07-AUG-2020 (EDW) (JDR)
Updated description of input argument "iverts".
Added -Parameters, -Exceptions, -Files, -Restrictions,
-Literature_References and -Author_and_Institution sections. Fixed
minor typos in header.
Edited the header to comply with NAIF standard. Added
example task statement.
Eliminated use of "lasterror" in rethrow.
Removed reference to the function's corresponding CSPICE header from
-Required_Reading section.
-Mice Version 1.0.0, 28-NOV-2016 (EDW)
expand triangular plate
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