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functions in pl3d.i  g
get3_centroid

get3_centroid(xyz, nxyz)
or get3_centroid(xyz)
return 3D centroids for polygons with vertices XYZ. If NXYZ is
specified, XYZ should be 3bysum(nxyz), with NXYZ being the
list of numbers of vertices for each polygon (as for the plfp
function). If NXYZ is not specified, XYZ should be a quadrilateral
mesh, 3bynibynj (as for the plf function). In the first case,
the return value is 3bynumberof(NXYZ); in the second case, the
return value is 3by(ni1)by(nj1).
The centroids are constructed as the mean value of all vertices
of each polygon.
interpreted function, defined at i/pl3d.i line 480

SEE ALSO:

get3_normal,
get3_light

get3_light

get3_light(xyz, nxyz)
or get3_light(xyz)
return 3D lighting for polygons with vertices XYZ. If NXYZ is
specified, XYZ should be 3bysum(nxyz), with NXYZ being the
list of numbers of vertices for each polygon (as for the plfp
function). If NXYZ is not specified, XYZ should be a quadrilateral
mesh, 3bynibynj (as for the plf function). In the first case,
the return value is numberof(NXYZ); in the second case, the
return value is (ni1)by(nj1).
The parameters of the lighting calculation are set by the
light3 function.
interpreted function, defined at i/pl3d.i line 363

SEE ALSO:

light3,
set3_object,
get3_normal,
get3_centroid

get3_normal

get3_normal(xyz, nxyz)
or get3_normal(xyz)
return 3D normals for polygons with vertices XYZ. If NXYZ is
specified, XYZ should be 3bysum(nxyz), with NXYZ being the
list of numbers of vertices for each polygon (as for the plfp
function). If NXYZ is not specified, XYZ should be a quadrilateral
mesh, 3bynibynj (as for the plf function). In the first case,
the return value is 3bynumberof(NXYZ); in the second case, the
return value is 3by(ni1)by(nj1).
The normals are constructed from the cross product of the lines
joining the midpoints of two edges which as nearly quarter the
polygon as possible (the medians for a quadrilateral). No check
is made that these not be parallel; the returned "normal" is
[0,0,0] in that case. Also, if the polygon vertices are not
coplanar, the "normal" has no precisely definable meaning.
interpreted function, defined at i/pl3d.i line 421

SEE ALSO:

get3_centroid,
get3_light

get3_xy

get3_xy, xyz, x, y
or get3_xy, xyz, x, y, z, 1
Given 3byanything coordinates XYZ, return X and Y in viewer's
coordinate system (set by rot3, mov3, orient3, etc.). If the
fifth argument is present and nonzero, also return Z (for use
in sort3d or get3_light, for example). If the camera position
has been set to a finite distance with setz3, the returned
coordinates will be tangents of angles for a perspective
drawing (and Z will be scaled by 1/zc).
interpreted function, defined at i/pl3d.i line 520

SEE ALSO:

sort3d,
get3_light,
rot3,
setz3,
set3_object

gnomon

gnomon
or gnomon, onoff
Toggle the gnomon display. If ONOFF is nonnil and nonzero,
turn on the gnomon. If ONOFF is zero, turn off the gnomon.
The gnomon shows the X, Y, and Z axis directions in the
object coordinate system. The directions are labeled.
The gnomon is always infinitely far behind the object
(away from the camera).
There is a mirrorthroughthescreenplane ambiguity in the
display which is resolved in two ways: (1) The (X,Y,Z)
coordinate system is righthanded, and (2) If the tip of an
axis projects into the screen, it's label is drawn in opposite
polarity to the other text on the screen.
interpreted function, defined at i/pl3d.i line 734

