Difference between revisions of "Part Module"
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(Another simple object used in 2D geometrical objects is Part Part2DObject, which is the base of Sketcher SketchObject (Sketcher), and most Draft elements.)
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Another simple object used in 2D geometrical objects is [[Part Part2DObject|Part Part2DObject]], which is the base of [[Sketcher Workbench|
Another simple object used in 2D geometrical objects is [[Part Part2DObject|Part Part2DObject]], which is the base of [[Sketcher Workbench|]], and most [[Draft Workbench|Draft elements]].
=== Examples === <!--T:20-->
=== Examples === <!--T:20-->
Revision as of 06:45, 30 November 2019
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 modelling 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.
The Part Workbench is the basic layer that exposes the OCCT drawing functions to all workbenches in FreeCAD
The tools are all located in the Part menu.
These are tools for creating primitive objects.
- Box: Draws a box by specifying its dimensions
- Cylinder: Draws a cylinder by specifying its dimensions
- Sphere: Draws a sphere by specifying its dimensions
- Cone: Draws a cone by specifying its dimensions
- Torus: Draws a torus (ring) by specifying its dimensions
- CreatePrimitives: A tool to create various parametric geometric primitives
- Shapebuilder: A tool to create more complex shapes from various parametric geometric primitives
These are tools for modifying existing objects. They will allow you to choose which object to modify.
- Extrude: Extrudes planar faces of an object
- Revolve: Creates a solid by revolving another object (not solid) around an axis
- Mirror: Mirrors the selected object on a given mirror plane
- Fillet: Fillets (rounds) edges of an object
- Chamfer: Chamfers edges of an object
- Ruled Surface:
- Loft: Lofts from one profile to another
- Sweep: Sweeps one or more profiles along a path
- Offset tools:
- Thickness: Hollows out a solid, leaving openings next to select faces.
- 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. introduced in version 0.19
- Compound Tools:
- Booleans: Performs boolean operations on objects
- Union: Fuses (unions) two objects
- Common: Extracts the common (intersection) part of two objects
- Cut: Cuts (subtracts) one object from another
- Join features: smart booleans for walled objects (e.g., pipes) introduced in version 0.16
- Splitting tools: introduced in version 0.17
- Boolean fragments: makes all the pieces that can be obtained by Boolean operations between objects introduced in version 0.17
- Slice a part: tool to split shapes by intersection with other shapes
- Slice: Splits an object into pieces by intersections with another object introduced in version 0.17
- XOR: removes space shared by even number of objects (symmetric version of Cut) introduced in version 0.17
- Defeaturing: introduced in version 0.18
- Section: Creates a section by intersecting an object with a section plane
- Cross sections...:
- Attachment: attachment is a utility to attach an object to another one.
Measure: Allows linear and angular measurement between points, edges, and faces.
- Measure Linear allows you to make linear measurements.
- Measure Angular allows you to make angular measurements.
- Measure Refresh updates the measurements on screen.
- Clear All Clears all measurements.
- Toggle All shows or hides all measurements.
- Toggle 3D shows or hides 3D measurements.
- Toggle Delta shows or hides delta measurements.
- Import: This tool allows you to add a file *.IGES, *.STEP, *.BREP to the current document.
- Export: This tool allows you to export a part object in a *.IGES, *.STEP, *.BREP file.
- BoxSelection: add to the selection the faces of the shapes that are touches by the rectangular selection. introduced in version 0.19
- Shape from Mesh: Creates a shape object from a mesh object.
- Points from mesh: creates a shape object made of points from the mesh. introduced in version 0.19
- 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:
- Create simple copy: Creates a simple copy of the selected object.
- Create transformed copy: creates a transformed copy of the selected object. introduced in version 0.19
- Create shape element copy: creates a copy from an element (vertex, edge, face) of the selected object. introduced in version 0.19
- Refine shape: Cleans faces by removing unnecessary lines.
- Check geometry: Checks the geometry of selected objects for errors.
- Preference ... Import Export
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.
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.
The "Part::TopoShape" is the geometrical object that is seen on screen. Essentially all workbenches use these TopoShapes internally to build and display edges, faces, and solids.
See also: 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 DataPlacement property, and basic properties to define its color and appearance.
To create a line element switch to the Python console and type in:
import Part,PartGui doc=App.newDocument() l=Part.LineSegment() l.StartPoint=(0.0,0.0,0.0) l.EndPoint=(1.0,1.0,1.0) doc.addObject("Part::Feature","Line").Shape=l.toShape() doc.recompute()
Let's go through the above python example step by step:
import Part,PartGui doc=App.newDocument()
loads the Part module and creates a new document
l=Part.LineSegment() l.StartPoint=(0.0,0.0,0.0) l.EndPoint=(1.0,1.0,1.0)
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 circle can be created in a similar way:
import Part doc = App.activeDocument() c = Part.Circle() c.Radius=10.0 f = doc.addObject("Part::Feature", "Circle") f.Shape = c.toShape() doc.recompute()
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:
s = f.Shape e = s.Edges c = e.Curve
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.