The PLplot Plotting Library: Programmer's Reference Manual  

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plpoly3
: Draw a polygon in 3 space
Draws a polygon in 3 space defined by n
points in
x
,
y
, and
z
.
Setup like plline3
, but differs from that function in that plpoly3
attempts to determine if the polygon is viewable depending on the
order of the points within the arrays and the value of
ifcc
. If the back of
polygon is facing the viewer, then it isn't drawn. If this isn't what
you want, then use plline3
instead.
The points are assumed to be in a plane, and the directionality of the plane is determined from the first three points. Additional points do not have to lie on the plane defined by the first three, but if they do not, then the determination of visibility obviously can't be 100% accurate... So if you're 3 space polygons are too far from planar, consider breaking them into smaller polygons. "3 points define a plane" :).
Bugs: If one of the first two segments is of zero length, or if they are colinear, the calculation of visibility has a 50/50 chance of being correct. Avoid such situations :). See x18c.c for an example of this problem. (Search for "20.1").

Redacted form: plpoly3(x, y, z, code)
This function is used in example 18.