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One of the advantages of CSG is that it can easily assure that objects are "solid" or
water-tight if all of the primitive shapes are water-tight. This can be important for
some manufacturing or engineering computation applications. By comparison, when
creating geometry based upon boundary representations, additional topological data
is required, or consistency checks must be performed to assure that the given
boundary description specifies a valid solid object.
A convenient property of CSG shapes is that it is easy to classify arbitrary points as
being either inside or outside the shape created by CSG. The point is simply
classified against all the underlying primitives and the resulting boolean expression is
evaluated. This is a desirable quality for some applications such as collision
detection.
2.2 STL Format and Slicing Technique
A STL file is a format used by Stereolithography software to generate information
needed to produce 3D models on Stereolithography machines.In fact, the extension
"stl" is said to be derived from the word “Stereolithography”. STL is a file format
native to the stereolithography CAD software created by 3D Systems. This file format
is supported by many software packages. It is widely used for rapid prototyping and
computer-aided manufacturing. STL files describe only the surface geometry of a
three dimensional object without any representation of color, texture or other
common CAD model attributes. The STL format specifies both ASCII and binary
representations. Binary files are more common, since they are more compact. A
sphere in STL format is shown below in fig 2.7
Fig 2.7 A Sphere in STL Format
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