Part Module/it

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Revision as of 20:14, 4 December 2013 by Renatorivo (talk | contribs) (Created page with "Potremmo dire, per riassumere, che le primitive geometriche sono blocchi di costruzione "informi", e le forme sono la reale geometria spaziale costruita su questi blocchi.")

The CAD capabilities of FreeCAD are based on the OpenCasCade kernel. The Part module allows FreeCAD to access and use the OpenCasCade objects and functions. OpenCascade is a professional-level CAD kernel, that features advanced 3D geometry manipulation and objects. The Part objects, unlike Mesh Module objects, are much more complex, and therefore permit much more advanced operations, like coherent boolean operations, modifications history and parametric behaviour.

Esempio di forma realizzata con il modulo Parte di FreeCAD

Gli strumenti

Gli strumenti del modulo Parte sono tutti situati nel menu Parte che viene visualizzato quando si carica questo modulo.

Template:Part Tools/it

Operazioni booleane

Un esempio di unione (Somma), intersezione (Comune) e differenza (Sottrazione)
Un esempio di unione (Somma), intersezione (Comune) e differenza (Sottrazione)

Un esempio di unione (Somma), intersezione (Comune) e differenza (Sottrazione)

Concetti base

Nella terminologia OpenCascade, si distingue tra primitive geometriche e forme (topologiche). Una primitiva geometrica può essere un punto, una linea, un cerchio, un piano, ecc o essere anche di tipo più complesso come una curva B-Spline o una superficie. Una forma può essere un vertice, un bordo, un profilo, una faccia, un solido o un insieme di più forme. Le primitive geometriche non sono fatte per essere visualizzate direttamente sulla scena 3D, ma piuttosto per essere utilizzate come geometrie per la costruzione di forme. Ad esempio, un bordo può essere costruito usando una linea o una porzione di un cerchio.

Potremmo dire, per riassumere, che le primitive geometriche sono blocchi di costruzione "informi", e le forme sono la reale geometria spaziale costruita su questi blocchi.

To get a complete list of all of them refer to the OCC documentation (Alternative: sourcearchive.com) and search for Geom_* (for geometry) and TopoDS_* (for shapes). There you can also read more about the differences between geometric objects and shapes. Please note that unfortunately 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 counter part.

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

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 now available to 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.

Examples

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

 import Part,PartGui 
 doc=App.newDocument()  
 l=Part.Line()
 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.Line()
 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.

 doc.addObject("Part::Feature","Line").Shape=l.toShape()

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.Line) 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.

 doc.recompute()

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

Note that a Line can be created by specifying its start and endpoint directly in the constructor, for example Part.Line(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[0]
 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.

Mesh Module
Drawing Module