Part Module/zh

Introduction
The solid modelling capabilities of FreeCAD are based on the Open Cascade Technology (OCCT) kernel, a professional-grade CAD system that features advanced 3D geometry creation and manipulation. The Part Workbench is a layer sitting on top of the OCCT libraries, that gives the user access to OCCT geometric primitives and functions. Essentially all 2D and 3D drawing functions in every workbench ( Draft, Sketcher,  PartDesign, etc.), are based on these functions exposed by the Part Workbench. Therefore, the Part Workbench is considered the core component of the modelling capabilities of FreeCAD.

The objects created with the Part Workbench are relatively simple; they are intended to be used with boolean operations (unions and cuts) in order to build more complex shapes. This modeling paradigm is known as the constructive solid geometry (CSG) workflow, and it was the traditional methodology used in early CAD systems. On the other hand, the PartDesign Workbench provides a more modern workflow to constructing shapes: it uses a parametrically defined sketch, that is extruded to form a basic solid body, which is then modified by parametric transformations (feature editing), until the final object is obtained.

Part objects are more complex than mesh objects created with the Mesh Workbench, as they permit more advanced operations like coherent boolean operations, modifications history, and parametric behaviour.



Tools
The tools are all located in the menu.

Primitives
These are tools for creating primitive objects.


 * [[Image:Part_Box.svg|32px]] Box: Draws a box by specifying its dimensions
 * [[Image:Part_Cylinder.svg|32px]] Cylinder: Draws a cylinder by specifying its dimensions
 * [[Image:Part_Sphere.svg|32px]] Sphere: Draws a sphere by specifying its dimensions
 * [[Image:Part_Cone.svg|32px]] Cone: Draws a cone by specifying its dimensions
 * [[Image:Part_Torus.svg|32px]] Torus: Draws a torus (ring) by specifying its dimensions
 * [[Image:Part_Primitives.svg|32px]] Primitives: A tool to add any of the defined geometric primitives.
 * [[Image:Part_Shapebuilder.svg|32px]] Shapebuilder: A tool to create more complex shapes from various parametric geometric primitives

Modifying objects
These are tools for modifying existing objects. They will allow you to choose which object to modify.


 * [[Image:Part_Extrude.svg|32px]] Extrude: Extrudes planar faces of an object
 * [[Image:Part_Revolve.svg|32px]] Revolve: Creates a solid by revolving another object (not solid) around an axis
 * [[Image:Part_Mirror.svg|32px]] Mirror: Mirrors the selected object on a given mirror plane
 * [[Image:Part_Fillet.svg|32px]] Fillet: Fillets (rounds) edges of an object
 * [[Image:Part_Chamfer.svg|32px]] Chamfer: Chamfers edges of an object
 * [[Image:Part_RuledSurface.svg|32px]] Ruled Surface:
 * [[Image:Part_Loft.svg|32px]] Loft: Lofts from one profile to another
 * [[Image:Part_Sweep.svg|32px]] Sweep: Sweeps one or more profiles along a path


 * [[Image:Part_CompOffsetTools.png|48px]] Offset tools:
 * [[Image:Part_Offset.svg|32px]] 3D Offset: Constructs a parallel shape at a certain distance from original.
 * [[Image:Part_Offset2D.svg|32px]] 2D Offset: Constructs a parallel wire at certain distance from original, or enlarges/shrinks a planar face.


 * [[Image:Part_Thickness.svg|32px]] Thickness: Hollows out a solid, leaving openings next to select faces.


 * [[Image:Part_ProjectionOnSurface.png|32px]] Projection on surface: Project a logo, text or any face,wire,edge to a surface. With the projection part it is possible to create a solid or wire.


 * [[Image:Part_Compound.svg|48px]] Compound Tools:
 * [[Image:Part_Compound.svg|32px]] Make compound: Creates a compound from the selected objects.
 * [[Image:Part_ExplodeCompound.svg|32px]] Explode Compound: Tool to split up compounds of shapes
 * [[Image:Part Compound‏‎Filter.svg|32px]] Compound Filter: The CompoundFilter can be used to extract the individual pieces.


 * [[Image:Part_Booleans.svg|32px]] Boolean: Performs boolean operations on objects
 * [[Image:Part_Fuse.svg|32px]] Union: Fuses (unions) two objects
 * [[Image:Part_Common.svg|32px]] Common: Extracts the common (intersection) part of two objects
 * [[Image:Part_Cut.svg|32px]] Cut: Cuts (subtracts) one object from another


 * [[Image:Part_CompJoinFeatures.png|48px]] Join features: smart booleans for walled objects (e.g., pipes)
 * [[Image:Part_JoinConnect.svg|32px]] Connect: Connects interiors of objects
 * [[Image:Part_JoinEmbed.svg|32px]] Embed: Embeds a walled object into another walled object
 * [[Image:Part_JoinCutout.svg|32px]] Cutout: Creates a cutout in a wall of an object for another walled object


 * [[Image:Part_CompSplittingTools.png|48px]] Splitting tools:
 * [[Image:Part_BooleanFragments.svg|32px]] Boolean fragments: makes all the pieces that can be obtained by Boolean operations between objects
 * [[Image:Part SliceApart.svg|32px]] Slice a part: tool to split shapes by intersection with other shapes
 * [[Image:Part_Slice.svg|32px]] Slice: Splits an object into pieces by intersections with another object
 * [[Image:Part_XOR.svg|32px]] XOR: removes space shared by even number of objects (symmetric version of Cut)


 * [[Image:Part Defeaturing.svg|32px]] Defeaturing:
 * [[Image:Part_Section.svg|32px]] Section: Creates a section by intersecting an object with a section plane
 * [[Image:Part_CrossSections.svg|32px]] Cross sections...: Creates one or more cross-sections through a selected shape
 * [[Image:Part Attachment.svg|32px]] Attachment: attachment is a utility to attach an object to another one.

Measure
Measure: Allows linear and angular measurement between points, edges, and faces.


 * [[Image:Part_Measure_Linear.svg|32px]] Measure Linear allows you to make linear measurements.
 * [[Image:Part_Measure_Angular.svg|32px]] Measure Angular allows you to make angular measurements.
 * [[Image:Part_Measure_Refresh.svg|32px]] Measure Refresh updates the measurements on screen.
 * [[Image:Part_Measure_Clear_All.svg|32px]] Clear All Clears all measurements.
 * [[Image:Part_Measure_Toggle_All.svg|32px]] Toggle All shows or hides all measurements.
 * [[Image:Part_Measure_Toggle_3d.svg|32px]] Toggle 3D shows or hides 3D measurements.
 * [[Image:Part_Measure_Toggle_Delta.svg|32px]] Toggle Delta shows or hides delta measurements.

Other tools

 * [[Image:Part_Import.svg|32px]] Import: This tool allows you to add a file *.IGES, *.STEP, *.BREP to the current document.
 * [[Image:Part_Export.svg|32px]] Export: This tool allows you to export a part object in a *.IGES, *.STEP, *.BREP file.
 * Part_BoxSelection.svg BoxSelection: add to the selection the faces of the shapes that are touches by the rectangular selection.
 * [[Image:Part_ShapeFromMesh.svg|32px]] Shape from Mesh: Creates a shape object from a mesh object.
 * Part_PointsFromMesh.svg Points from mesh: creates a shape object made of points from the mesh.
 * Convert to solid: Converts a shape object to a solid object.
 * Reverse shapes: Flips the normals of all faces of the selected object.


 * Create a copy:
 * [[Image:Part_SimpleCopy‎.svg|32px]] Create simple copy: Creates a simple copy of the selected object.
 * Part_TransformedCopy.svg Create transformed copy: creates a transformed copy of the selected object.
 * Part_ElementCopy.svg Create shape element copy: creates a copy from an element (vertex, edge, face) of the selected object.
 * [[Image:Part_RefineShape.svg|32px]] Refine shape: Cleans faces by removing unnecessary lines.


 * [[Image:Part_CheckGeometry.svg|32px]] Check geometry: Checks the geometry of selected objects for errors.

Preferences

 * [[Image:Preferences-part_design.svg|32px]] Preferences: preferences available for Part Tools (the Part workbench also uses the PartDesign Preferences).
 * [[Image:Preferences-import-export.svg|32px]] Import-Export Preferences: preferences available for importing from and exporting to different file formats.
 * Fine-tuning: some extra parameters to fine-tune Part behavior.

OCCT geometric concepts
In OpenCascade terminology, we distinguish between geometric primitives and topological shapes. A geometric primitive can be a point, a line, a circle, a plane, etc. or even some more complex types like a B-Spline curve or a surface. A shape can be a vertex, an edge, a wire, a face, a solid or a compound of other shapes. The geometric primitives are not made to be directly displayed on the 3D scene, but rather to be used as building geometry for shapes. For example, an edge can be constructed from a line or from a portion of a circle.

In summary, geometry primitives are "shapeless" building blocks, while topological shapes are the real objects built on them.

A complete list of all primitives and shapes refer to the OCC documentation (Alternative: sourcearchive.com) and search for Geom_* (for geometric primitives) and TopoDS_* (for shapes). There you can also read more about the differences between them. Please note that the official OCC documentation is not available online (you must download an archive) and is mostly aimed at programmers, not at end-users. But hopefully you'll find enough information to get started here. Also see Modeling Data User's Guide.

''At a very high level, topology tells what pieces an object is made of, and the logical relationships between them. A shape is made of a certain set of faces. A face is bounded by a certain set of edges. Two faces are adjacent if they share a common edge.''

''Topology alone does not tell you the size, curvature, or 3D locations of any of those pieces. However, each piece of topology does knows about it's underlying geometry. A face knows what surface it lies on. An edge knows what curve it lies on. The geometry knows about curvature and location in space.'' - Source

Thus, Topology defines the relationship between simple geometric entities, which can be linked together to represent complex shapes. - Modeling Data User's Guide



Note: Only 3 types of topological objects have geometric representations – vertex, edge, and face (Source).

The geometric types actually can be divided into two major groups: curves and surfaces. Out of the curves (line, circle, ...) you can directly build an edge, out of the surfaces (plane, cylinder, ...) a face can be built. For example, the geometric primitive line is unlimited, i.e. it is defined by a base vector and a direction vector while its shape representation must be something limited by a start and end point. And a box -- a solid -- can be created by six limited planes.

From an edge or face you can also go back to its geometric primitive counterpart.

Thus, out of shapes you can build very complex parts or, the other way round, extract all sub-shapes a more complex shape is made of.



Scripting
Part scripting

The main data structure used in the Part module is the BRep data type from OpenCascade. Almost all contents and object types of the Part module are available by Python scripting. This includes geometric primitives, such as Line and Circle (or Arc), and the whole range of TopoShapes, like Vertexes, Edges, Wires, Faces, Solids and Compounds. For each of those objects, several creation methods exist, and for some of them, especially the TopoShapes, advanced operations like boolean union/difference/intersection are also available. Explore the contents of the Part module, as described in the FreeCAD Scripting Basics page, to know more.

The most basic object that can be created is a Part Feature, which has a simple property, and basic properties to define its color and appearance.

Another simple object used in 2D geometrical objects is Part Part2DObject, which is the base of Sketcher SketchObject (Sketcher), and most Draft elements.

Test script
Test the creation of Part Primitives with a script.

This script is located in the installation directory of the program, and can be examined to see how the basic primitives are built.

Examples
To create a line element switch to the Python console and type in:

Let's go through the above python example step by step:

loads the Part module and creates a new document

Line is actually a line segment, hence the start and endpoint.

This adds a Part object type to the document and assigns the shape representation of the line segment to the 'Shape' property of the added object. It is important to understand here that we used a geometric primitive (the Part.LineSegment) to create a TopoShape out of it (the toShape method). Only Shapes can be added to the document. In FreeCAD, geometry primitives are used as "building structures" for Shapes.

Updates the document. This also prepares the visual representation of the new part object.

Note that a Line Segment can be created by specifying its start and endpoint directly in the constructor, for example Part.LineSegment(point1,point2), or we can create a default line and set its properties afterwards, as we did here.

A Line can be created also using:

A circle can be created in a similar way:

or using:

Note again, we used the circle (geometry primitive) to construct a shape out of it. We can of course still access our construction geometry afterwards, by doing:

Here we take the shape of our object f, then we take its list of edges. In this case there will be only one because we made the whole shape out of a single circle, so we take only the first item of the Edges list, and we takes its curve. Every Edge has a Curve, which is the geometry primitive it is based on.

Head to the Topological data scripting page if you would like to know more.

Tutorials

 * Import from STL or OBJ : How to import STL/OBJ files in FreeCAD
 * Export to STL or OBJ : How to export STL/OBJ files from FreeCAD
 * Whiffle Ball tutorial : How to use the Part Module