📄 3.3.3 三维图元的输出.htm
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<H3><FONT face=楷体_GB2312 size=4><SPAN lang=EN-US>3.3.3 </SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">三维图元的输出</SPAN></FONT></H3>
<P class=MsoNormal> <FONT face=楷体_GB2312 size=4> </FONT><FONT
face=楷体_GB2312 size=4><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">从命令形式上看，在很多图形软件中，三维图元的输出只是在原来二维图元输出命令的基础上增加一个后缀</SPAN><SPAN
lang=EN-US>3</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">，如</SPAN><SPAN
lang=EN-US>move</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">的</SPAN><SPAN
lang=EN-US>3</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">维形式的：</SPAN><SPAN
lang=EN-US>move-3(x,y,z)</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">，</SPAN><SPAN
lang=EN-US>line</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">的三维形式为：</SPAN><SPAN
lang=EN-US>dine-3(x,y,z)</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">，</SPAN><SPAN
lang=EN-US>Polyline</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">的三维形式为：</SPAN><SPAN
lang=EN-US>polyline-3(n,x-array,y_array,z_array)</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">。实际上，要在图形输出设备上输出一个三维图元，必须进行投影变换，为与前面所提供的投影变换相一致。我们假定其视域坐标系统</SPAN><SPAN
lang=EN-US>(Viewig coordinate System</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">简称</SPAN><SPAN
lang=EN-US>VCS)</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">定义为：投影面与</SPAN><SPAN
lang=EN-US>xoy</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">坐标而重合；</SPAN><SPAN
lang=EN-US>z</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">轴正向指间要表达的物体；透视投影的中心位于</SPAN><SPAN
lang=EN-US>z</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">轴的负轴之上。</SPAN></FONT></P>
<P class=MsoNormal style="TEXT-INDENT: 21pt"><SPAN
style="mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman"><FONT
face=楷体_GB2312 size=4>要将三维图元输出到图形设备上，必须通过以下步骤：</FONT></SPAN></P>
<P class=MsoNormal
style="MARGIN: 1px 0px; TEXT-INDENT: 0px; LINE-HEIGHT: 150%"><SPAN
lang=EN-US><FONT face=楷体_GB2312 size=4>1 </FONT></SPAN><FONT
face=楷体_GB2312 size=4><SPAN
style="mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">定义一个视域坐标系统</SPAN><SPAN
lang=EN-US>VCS</SPAN><SPAN
style="mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">，为此需指定如下数：</SPAN></FONT></P>
<P class=MsoNormal
style="MARGIN: 1px 0px; TEXT-INDENT: 0px; LINE-HEIGHT: 150%"><SPAN lang=EN-US
style="mso-spacerun: yes"><FONT face=楷体_GB2312 size=4>
</FONT></SPAN><FONT face=楷体_GB2312 size=4><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">·</SPAN><SPAN
lang=EN-US>VCS</SPAN><SPAN
style="mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">坐标原点，也称</SPAN><SPAN
lang=EN-US>View reference pont;</SPAN></FONT></P>
<P class=MsoNormal
style="MARGIN: 1px 0px; TEXT-INDENT: 0px; LINE-HEIGHT: 150%"><SPAN lang=EN-US
style="mso-spacerun: yes"><FONT face=楷体_GB2312 size=4>
</FONT></SPAN><FONT face=楷体_GB2312 size=4><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">·</SPAN><SPAN
lang=EN-US>VCS</SPAN><SPAN
style="mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">的</SPAN><SPAN
lang=EN-US>z</SPAN><SPAN
style="mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">轴方向，也称</SPAN><SPAN
lang=EN-US>view plane normal, xoy</SPAN><SPAN
style="mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">平面称为</SPAN><SPAN
lang=EN-US>vierpin</SPAN><SPAN
style="mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">。</SPAN></FONT></P>
<P class=MsoNormal
style="MARGIN: 1px 0px; TEXT-INDENT: 0px; LINE-HEIGHT: 150%"><SPAN lang=EN-US
style="mso-spacerun: yes"><FONT face=楷体_GB2312 size=4>
</FONT></SPAN><FONT face=楷体_GB2312 size=4><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">·</SPAN><SPAN
lang=EN-US>VCS</SPAN><SPAN
style="mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">的</SPAN><SPAN
lang=EN-US>y</SPAN><SPAN
style="mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">轴方向，又称</SPAN><SPAN
lang=EN-US>view up vector</SPAN><SPAN
style="mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">。</SPAN></FONT></P>
<P class=MsoNormal
style="MARGIN: 1px 0px; TEXT-INDENT: 0px; LINE-HEIGHT: 150%"><SPAN
lang=EN-US><FONT face=楷体_GB2312 size=4>2</FONT></SPAN><FONT face=楷体_GB2312
size=4><SPAN
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