Part scripting: Difference between revisions

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s = f.Shape
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edge = shape.Edges[0]
c = e.Curve
curve = edge.Curve
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Revision as of 19:58, 13 February 2022

Introduction

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.

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

See also

Test script

Test the creation of Part Primitives with a script. introduced in version 0.19

import parttests.part_test_objects as pto
pto.create_test_file("example_file")

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

$INSTALL_DIR/Mod/Part/parttests/part_test_objects.py

Examples

Line

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

import FreeCAD as App
import Part

doc = App.newDocument()

line = Part.LineSegment()
line.StartPoint = (0.0, 0.0, 0.0)
line.EndPoint = (1.0, 1.0, 1.0)
obj = doc.addObject("Part::Feature", "Line")
obj.Shape= line.toShape()

doc.recompute()

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

import FreeCAD as App
import Part
doc = App.newDocument()

loads the FreeCAD and Part modules and creates a new document

line = Part.LineSegment()
line.StartPoint = (0.0, 0.0, 0.0)
line.EndPoint = (1.0, 1.0, 1.0)

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

obj = doc.addObject("Part::Feature", "Line")
obj.Shape= line.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.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.

doc.recompute()

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 also be created using:

import FreeCAD as App
import Part

def my_create_line(pt1, pt2, obj_name):
    obj = App.ActiveDocument.addObject("Part::Line", obj_name)
    obj.X1 = pt1[0]
    obj.Y1 = pt1[1]
    obj.Z1 = pt1[2]

    obj.X2 = pt2[0]
    obj.Y2 = pt2[1]
    obj.Z2 = pt2[2]

    App.ActiveDocument.recompute()
    return obj

line = my_create_line((0, 0, 0), (0, 10, 0), "LineName")

Circle

A circle can be created in a similar way:

import FreeCAD as App
import Part

doc = App.activeDocument()

circle = Part.Circle() 
circle.Radius = 10.0  
obj = doc.addObject("Part::Feature", "Circle")
obj.Shape = circle.toShape()

doc.recompute()

or using:

import FreeCAD as App
import Part

def my_create_circle(rad, obj_name):
    obj = App.ActiveDocument.addObject("Part::Circle", obj_name)
    obj.Radius = rad

    App.ActiveDocument.recompute()
    return obj

circle = my_create_circle(5.0, "CircleName")

or create a circle defined by it's center, axis and radius using:

import FreeCAD as App
import Part

doc = App.activeDocument()

center = App.Vector(1, 2, 3)
axis = App.Vector(1, 1, 1)
radius = 10
circle = Part.Circle(center, axis, radius)
obj = doc.addObject("Part::Feature", "Circle")
obj.Shape = circle.toShape()

doc.recompute()

or create a circle defined by three points using:

import FreeCAD as App
import Part

doc = App.activeDocument()

p1 = App.Vector(10, 0, 0)
p2 = App.Vector(0, 10, 0)
p3 = App.Vector(0, 0, 10)
circle = Part.Circle(p1, p2, p3)
obj = doc.addObject("Part::Feature", "Circle")
obj.Shape = circle.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:

shape = obj.Shape
edge = shape.Edges[0]
curve = edge.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.

Arc

An arc can be created like this:

import Part
doc = App.activeDocument()
p1 = App.Vector(10,0,0)
p2 = App.Vector(0,10,0)
p3 = App.Vector(-10,0,0)
c = Part.Arc(p1,p2,p3)
f = doc.addObject("Part::Feature", "Arc")
f.Shape = c.toShape()
doc.recompute()

This draws a half circle. The center is at (0,0). The Radium is 10. P1 is the start point on + X axis. P2 is the middle point on + Y axis and P3 is the end point on -Y axis.

You can also create an arc as part of a circle like this:

import Part
doc = App.activeDocument()
p1 = App.Vector(10,0,0)
p2 = App.Vector(0,10,0)
p3 = App.Vector(-10,0,0)
c = Part.Circle(p1,p2,p3)
a=Part.ArcOfCircle(c,0.000000,0.762675)
f = doc.addObject("Part::Feature", "Arc")
f.Shape = a.toShape()
doc.recompute()

It needs a circle, Start angle and Finish angle.

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