/Polyhedron ... /EndPolyhedron
describes a general polyhedron composed of a set of 3D polygons.
Concave polygons are available but not recommended.
Lists of vertices and
facets are described between /Polyhedron and /EndPolyhedron.
The following is the format for a polyhedron with
N vertices and M facets.
| Format | /Polyhedron |
/Vertex x1 y1 z1 |
|
/Vertex x2 y2 z2 |
|
| ...... | |
/Vertex xN yN zN |
|
/Facet f1_v1 f1_v2 f1_v3 ... |
|
/Facet f2_v1 f2_v2 f2_v3 ... |
|
| ...... | |
/Facet fM_v1 fM_v2 fM_v3 ... |
|
/EndPolyhedron |
|
(xi, yi, zi) |
3D position of the i-th vertex |
| of the polyhedron (). | |
| The integer label `i'' is assigned to | |
| vertices incrementally, beginning from 1. | |
fa_vj |
the j-th vertex label of the a-th facet, |
| whose absolute value must coincide with | |
| one of the vertex labels {}. | |
fa_v1 fa_v2 fa_v3 ... |
the a-th facet expressed by connecting |
| vertex labels in counter-clock-wise order | |
| viewing from its front side. | |
Edge fa_vi--fa_vj is regarded as |
|
an invisible edge if fa_vj is negative. |
|
| At least three vertices must be described. |
Note that positive-integer labels are incrementally and automatically
assinged to vertices given by /Vertex ...,
beginning from 1, not 0.
An invisible edge is expressed by assigning a negative integer vertex label to its ending point. For example, ``/Facet 1 -2 6 5 ;'' describes a facet 12651, in which the edge connecting vertices 1 and 2 is invisible.
Vertex data (/Vertex ...) and facet data (/Facet ...)
can be described at any position with any order
between /Polyhedron ... /EndPolyhedron,
but it is recommended that all vertex data are described beforehand.
The following is a sample description of a
red box using
/Polyhedron .../EndPolyhedron.
Example: 1 box
##G4.PRIM-FORMAT-2.4 ################################################## # 1x4x9 box with /polyhedron ... /EndPolyhedron ## ################################################## /BoundingBox -0.5 -2.0 -4.5 0.5 2.0 4.5 !SetCamera !OpenDevice !BeginModeling /ColorRGB 1.0 0.0 0.0 /Polyhedron /Vertex -0.500000000 -2.000000000 -4.500000000 /Vertex 0.500000000 -2.000000000 -4.500000000 /Vertex -0.500000000 2.000000000 -4.500000000 /Vertex 0.500000000 2.000000000 -4.500000000 /Vertex -0.500000000 -2.000000000 4.500000000 /Vertex 0.500000000 -2.000000000 4.500000000 /Vertex -0.500000000 2.000000000 4.500000000 /Vertex 0.500000000 2.000000000 4.500000000 /Facet 3 4 2 1 /Facet 1 2 6 5 /Facet 2 4 8 6 /Facet 4 3 7 8 /Facet 3 1 5 7 /Facet 5 6 8 7 /EndPolyhedron !EndModeling !DrawAll !CloseDevice