Faceted Geometric Kernel - Faceted Boolean

FGK
	REPRESENTATION
	CREATE & EDIT
	BOOLEAN
	RENDER & SELECT

FGK | Functionalities | Faceted Boolean

Boolean Basics:

Target and tool
The operands of a boolean are called the target and the tool. The target of a boolean is the body you begin with, and the tool is the body you operate on it with. The target is modified by the tool, and the tool is deleted at the end of the operation. Faceted Boolean preserves the tags of entities in the target as far as possible. Following figure illustrate target, tool and possible Boolean output:

The following diagram shows the effect of swapping the target and tool of subtract:

Example of faceted boolean is shown in below figures:


Cube + Cylinder Union	Cube - Cylinder Subtraction

Cube Cylinder Intersection	Cylinder Remain

Similarly faceted boolean can also perform general body boolean i.e. non-manifold boolean as shown in figures:


Shared Edge	Shared Face

Type of boolean

There are two types of booleans mostly used in CAD modeling:

Global Booleans
Global booleans perform boolean operations on whole bodies, taking a single target body, and multiple tool bodies, and applying the specified boolean operation to the target. Because the operation is performed at the body level (by comparing all pairs of faces in the target and tool), the resulting body is guaranteed to be topologically consistent. Global booleans, because of the nature of the face pair comparison, can be computationally expensive.

Local Booleans
Local booleans (sometimes known as partial booleans), tend to be very quick to perform compared to global booleans. Rather than working at the body level, local booleans use a set of faces from a target body, and a set of faces from a single tool body. User specifies these faces himself, and only the faces user specify are used in the boolean operation. Restricting the scope of the boolean operation in this way can drastically improve performance.

Sheet Booleans
Faceted Boolean provides functionality to perform sheet boolean. API used would be same as above only input parameters are changed. If booleans in subtract operation target is solid and tool is sheet then one can perform trimming operation whereas target is sheet and tool is solid produces punching operation.
Trimming operation are in particular highly useful in trimming unwanted features or removing cusp during CAD Repair.

Boolean Algorithm
A boolean may be a union, subtraction or intersection. The type of boolean performed can be selected by setting the 'function' field in the option structure. If no function code is supplied, the default action is union. Faceted Booleans may be thought of as being performed in four main phases. These are intersection, imprinting, gluing, and selection.

Intersection and Imprinting
First step of a boolean operation is to intersect the target and tool entities and imprint edges and vertices on them where they intersect. These imprinted edges and vertices form the boundaries of intersection between target and tool entities. These edges divide the faces of each body into face sets which are either inside, outside, or on the boundary of, the other bodies.

Gluing and Selection
The resulting sets of faces are glued together into a single intermediate body. The parts of the model which are to be kept or rejected are selected, according to the type of boolean being performed and the options supplied, using information gained in the earlier phases.

Options for Faceted Boolean
To modify and control the behaviour of Faceted Boolean an options structure will be passed main function. The following table summarizes the options available for global and sheet booleans:

Option	Description
function	The boolean operation to be performed: union, subtraction or intersection.
allow_disjoint	Whether to return a single disjoint body if the operation would result in more than one body.
fence	Modify the behavior of the subtract operation and determine which resultant bodies are returned when performing solid/ sheet (trimming) or sheet/solid (punching) boolean operations.
configuration	A sub-structure that describes the configuration of the target and tool bodies. (For optimizing boolean operations)
matched_region	A sub-structure that describes regions in the target and tool bodies that should be matched. When performing boolean operations in which there is a nearly coincident region between the target and tool bodies, user can specify that certain topological regions are matched when performing boolean functions. Doing this can produce better results, and make the boolean operation faster. A matched region is a region of overlap between two topological entities that are geometrically coincident to a specified tolerance. The entities in the matched region must be in the target or tools of the boolean operation. The following combinations of topological entities may be provided as matched regions : Vertex - Vertex Edge - Edge Face - Edge Face - Face
check_fa	Whether to check faces involved in the boolean operation - only faces which are adjacent to imprinted edges are checked. If the face checking is switched off, the boolean operation may produce an invalid body without raising an error. However, in some cases, if face checking is switched on the performance of the boolean operation may be reduced.
default_tol	The default tolerance to which the boolean operation, if it has to, may approximate entities or assume that entities are coincident. This value should be set to a value that is related to the tolerance to which the application is creating approximations. If this field is set to zero (0.0), it is assumed that the decision to set tolerances on entities is being left to the code.
max_tol	The maximum tolerance which may be applied to any entity involved in the boolean operation.
tracking	Request additional topological data on the result of the boolean, this is specific to the function being called. Within this function this option can be used to return additional tracking data when using a single, non-disjoint tool body.
nm_edge_repair	Whether to attempt to repair certain configurations of non-manifold results.

Optimizing local and global boolean operations
If the boolean operation involves instancing, i.e. a boolean operation which takes a single target body and a list of tool bodies, e.g. when drilling an array of holes in a body, the performance of the operation can be improved by using one of the following instancing options in the configuration option sub-structure:

Option	Description
no_tool_intersect	This option can be set when the set of tool bodies are known not to intersect each other, though they are allowed to clash with existing edges on the target (including the periphery edge).
no_loop_intersect	This option can be set when there is no interference between any instances and the existing edges of the target, though the tools can clash with each other

Boolean Examples
Following centrifugal pump assembly is processed in FGK based application to perform global boolean. Void space is filled and non-manfolid boolean part is created as output.