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[[Category:Objects]]
[[Category:Constructive Solid Geometry]]
{{#indexentry:CSG, union}}
{{#indexentry:union, keyword}}
{{#indexentry:keyword, union}}
<table class="centered" width="660x" cellpadding="0" cellspacing="10">
<tr>
<td>
[[Image:RefImgUnionobj.gif|center|640px]]
</td>
</tr>
<tr>
<td>
The union of two objects.
</td>
</tr>
</table>

The simplest kind of CSG is the <code>union</code>. The syntax is:
<pre>
UNION:
union {
OBJECTS...
[OBJECT_MODIFIERS...]
}
</pre>

Unions are simply glue used to bind two or more shapes into a single
entity that can be manipulated as a single object. The image above shows the
union of <code>A</code> and <code>B</code>. The new object created by the
union operation can be scaled, translated and rotated as a single shape. The
entire union can share a single texture but each object contained in the
union may also have its own texture, which will override any texture
statements in the parent object.

You should be aware that the surfaces inside the union will not be removed.
As you can see from the figure this may be a problem for transparent unions.
If you want those surfaces to be removed you will have to use the <code>
merge</code> operations explained in a later section.

The following union will contain a box and a sphere.
<pre>
union {
box { <-1.5, -1, -1>, <0.5, 1, 1> }
cylinder { <0.5, 0, -1>, <0.5, 0, 1>, 1 }
}
</pre>

{{#indexentry:composite}}
Earlier versions of POV-Ray placed restrictions on unions so you often had
to combine objects with <code>composite</code> statements. Those earlier
restrictions have been lifted so <code>composite</code> is no longer needed.
It is still supported for backwards compatibility.

{{#indexentry:split_union, union}}
{{#indexentry:keyword, split_union}}
==Split_Union==
<code>split_union</code> is a boolean keyword that can be added to a union.
It has two states <code>on</code>/<code>off</code>, its default is <code>on</code>.

<code>split_union</code> is used when [[Reference:Photons#Shooting Photons at an Object|photons]] are shot
at the CSG-object. The object is split up in its compound parts, photons are shot at
each part separately. This is to prevent photons from being shot at 'empty spaces' in the object,
for example the holes in a grid. With compact objects, without 'empty spaces'
<code>split_union off</code> can improve photon
gathering.
<pre>
union {
object {...}
object {...}
split_union off
}
</pre>

@@ Line 53: / Line 53: @@
 It is still supported for backwards compatibility.</p>
 {{#indexentry:split_union, union}}
 {{#indexentry:keyword, split_union}}
 <p><code>split_union</code> is a boolean keyword that can be added to a union.
 It has two states <code>on</code>/<code>off</code>, its default is <code>on</code>.</p>

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