Manual:Creating and manipulating geometry/es

En los capítulos anteriores, hemos aprendido sobre los diferentes ambientes de trabajo de FreeCAD, y cómo cada uno de ellos implementa sus propias herramientas y tipos de geometría. El mismo concepto se aplica cuando se trabaja desde el código de Python.

También vimos que la gran mayoría de los ambientes de trabajo de FreeCAD dependen de uno muy fundamental: el Ambiente de trabajo Pieza. De hecho, muchos otros ambientes de trabajo, como Borrador y Arquitectura, hacen exactamente lo que haremos en este capítulo: usar código Python para crear y manipular la geometría de la Pieza.

Así que lo primero que tenemos que hacer para trabajar con la geometría Pieza, es hacer el equivalente en Python a cambiar al Ambiente de trabajo Pieza: importar el módulo Pieza:

Tómese un minuto para explorar el contenido del módulo Pieza, escribiendo Pieza. y navegando por los diferentes métodos disponibles. El módulo Pieza ofrece varias funciones convenientes como makeBox, makeCircle, etc... que construirán instantáneamente un objeto para usted. Pruebe esto, por ejemplo:

When you press Enter after typing the line above, nothing will appear in the 3D view, but something like this will be printed on the Python Console:

This is where an important concept takes place. What we created here is a Part Shape. It is not a FreeCAD document object (yet). In FreeCAD, objects and their geometry are independent. Think of a FreeCAD document object as a container, that will host a shape. Parametric objects will also have properties such as Length and Width, and will recalculate their Shape on-the-fly, whenever one of the properties changes. What we did here is calculate a shape manually.

We can now easily create a "generic" document object in the current document (make sure you have at least one new document open), and give it a box shape like the one we just made:

Note how we handled myObj.Shape, notice that it is done exactly like we did it in the previous chapter, when we changed other properties of an object, such as  box.Height = 5. In fact, Shape is also a property, just like Height. Only it takes a Part Shape, not a number. In the next chapter we will have a better look at how these parametric objects are constructed.

For now, let's explore our Part Shapes in more detail. At the end of the chapter about traditional modeling with the Part Workbench we showed a table that explains how Part Shapes are constructed, and their different components (Vertices, edges, faces, etc). The exact same components exist here and can be retrieved from Python. Part Shapes always have the following attributes: Vertexes, Edges, Wires, Faces, Shells and Solids. All of them are lists, that can contain any number of elements or be empty:

For example, let's find the area of each face of our box shape above:

Or, for each edge, its start point and end point:

As you see, if our boxShape has a "Vertexes" attribute, each Edge of the boxShape also has a "Vertexes" attribute. As we can expect, the boxShape will have 8 vertices, while the edge will only have 2, which are both part of the list of 8.

We can always check what is the type of a shape:

So to resume the topic of Part Shapes: Everything starts with Vertices. With one or two vertices, you form an Edge (full circles have only one vertex). With one or more Edges, you form a Wire. With one or more closed Wires, you form a Face (the additional Wires become "holes" in the Face). With one or more Faces, you form a Shell. When a Shell is fully closed (watertight), you can form a Solid from it. And finally, you can join any number of Shapes of any types together, which is then called a Compound.

We can now try creating complex shapes from scratch, by constructing all their components one by one. For example, let's try to create a volume like this:



We will start by creating a planar shape like this:



First, let's create the four base points:

Then we can create the two linear segments:



Note that we didn't need to create Vertices. We could immediately create Part.LineSegments from FreeCAD Vectors. This is because here we haven't created Edges yet. A Part.LineSegment (as well as Part.Circle, Part.Arc, Part.Ellipse or Part.BSpline) does not create an Edge, but rather a base geometry on which an Edge will be created. Edges are always made from such a base geometry, which is stored in its Curve attribute. So if you have an Edge, doing:

will show you what kind of Edge it is, i.e. if it's based on a line, an arc, etc... But let's come back to our exercise, and build the arc segments. For this, we will need a third point, so we can use the convenient Part.Arc, which takes 3 points:



Now we have 2 lines (L1 and L2) and 2 arcs (C1 and C2). We need to turn them into edges:

Alternatively, base geometries also have a toShape function that do exactly the same thing:

Once we have a series of Edges, we can now form a Wire, by giving it a list of Edges. We do need to take care of the order.

And we can check if our Wire was correctly understood, and that it is correctly closed:

Which will print "True" or "False". In order to make a Face, we need closed Wires, so it is always a good idea to check that before creating the Face. Now we can create a Face, by giving it a single Wire (or a list of Wires if we want holes):

Then we extrude it:

Note that P is already a Solid:

This is because when we extrude a single Face, we always get a Solid. This wouldn't be the case, for example, if we had extruded the Wire instead:

Which will of course give us a hollow shell, with the top and bottom faces missing.

Now that we have our final Shape, we are anxious to see it on screen! So let's create a generic object, and assign our new Solid to it:

Como alternativa, el módulo Pieza también proporciona un acceso directo que realiza la operación anterior más rápidamente (pero no se puede elegir el nombre del objeto):

Todo lo anterior, y mucho más, se explica en detalle en la página Guionización Pieza, junto con ejemplos.

Leer más


 * El ambiente de trabajo Pieza
 * Guionización Pieza