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821
SECTION 9.5 3D Artwork
The C entry specifies the center of the cutting plane. This implies that the plane
passes through the center point, but it is also the point of reference when deter-
mining the orientation of the plane.
The O array indicates the orientation of the cutting plane, taking into account its
center. The orientation can be determined by a two-step process:
• The plane is situated such that it passes through point C, and oriented such that
it is perpendicular to the axis specified by the array entry whose value is null.
• For each of the other two axes, the plane is rotated the specified number of de-
grees around the associated axis, while maintaining C as a fixed point on the
plane. Since the two axes are perpendicular, the order in which the rotations are
performed is irrelevant.
The PO entry specifies the opacity of the plane itself when rendered, while the PC
entry provides its color. When the PO entry is greater than 0, a visual representa-
tion of the cutting plane is rendered with the 3D artwork. This representation is a
square with a side length equal to the length of the diagonal of the maximum
bounding box for the 3D artwork, taking into account any keyframe animations
present. When the PO entry is 0, no visible representation of the cutting plane is
rendered.
The IV entry is a boolean value that determines whether a visual indication is
drawn of the plane’s intersection with the 3D artwork. If such an indication is
drawn, the IC entry specifies its color.
The Example 9.3 describes a set of views and corresponding cross sections that il-
lustrate the various effects of orientation.
Example 9.3
3 0 obj %CrossSection1
<<
/Type /3DCrossSection
/C [0 0 0]
/O [null 0 0]
/PO 0.35
/PC [/DeviceRGB 0.75 0.86 1]
/IV true
/IC [/DeviceRGB 0 1 0]
>>
endobj
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