Part Feature

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Introduction

Tree Part.svg

A Part Feature object, or formally a Part::Feature, is a simple element with a topological shape associated to it that can be displayed in the 3D view.

A Part Feature is the parent class of most 2D (Draft, Sketcher) and 3D (Part, PartDesign) objects, with the exception of meshes, which are normally based on Mesh Feature, or Fem FemMeshObject for FEM objects.

Every object created with the Part Workbench is essentially a Part Feature.

FreeCAD core objects.svg

Simplified diagram of the relationships between the core objects in the program. The Part::Feature class is the origin of most 2D (Draft, Sketcher) and 3D (Part, PartDesign) objects that have a Part TopoShape.


Usage

The Part Feature is an internal object, so it cannot be created from the graphical interface, only from the Python console as described in the Scripting section.

The Part::Feature is defined in the Part Workbench but can be used as the base class for scripted objects in all workbenches that produce 2D and 3D geometrical shapes. Essentially all objects produced in the Part Workbench are instances of a Part::Feature. Solid objects imported from STEP or BREP files will be imported using the Part Workbench, so they will also be imported as Part::Feature elements albeit without parametric history.

Part::Feature is also the parent class of the PartDesign Body, of the PartDesign Features, and of the Part Part2DObject, which is specialized for 2D (planar) shapes.

A Part::Feature has simple properties like a placement, and visual properties to define the appearance of its vertices, edges, and faces. Workbenches can add more properties to this basic element to produce an object with complex behavior.

Properties

A Part Feature (Part::Feature class) is derived from the basic App GeoFeature (App::GeoFeature class), therefore it shares all the latter's properties.

In addition to the properties described in App GeoFeature, the Part Feature has the DataShape property, which stores the Part TopoShape of this object; this is the geometry that is shown in the 3D view.

Other properties that this object has are those related to the appearance of its TopoShape, including ViewAngular Deflection, ViewDeviation, ViewDraw Style, ViewLighting, ViewLine Color, ViewLine Width, ViewPoint Color, ViewPoint Size, and also the hidden properties ViewDiffuse Color, ViewLine Color Array, ViewLine Material, ViewPoint Color Array, and ViewPoint Material.

See Property for all property types that scripted objects can have.

These are the properties available in the property editor. Hidden properties can be shown by using the Show all command in the context menu of the property editor.

Data

Base

  • DataPlacement (Placement): the position of the object in the 3D view. The placement is defined by a Base point (vector), and a Rotation (axis and angle). See Placement.
    • DataAngle: the angle of rotation around the DataAxis. By default, it is (zero degrees).
    • DataAxis: the unit vector that defines the axis of rotation for the placement. Each component is a floating point value between 0 and 1. If any value is above 1, the vector is normalized so that the magnitude of the vector is 1. By default, it is the positive Z axis, (0, 0, 1).
    • DataPosition: a vector with the 3D coordinates of the base point. By default, it is the origin (0, 0, 0).
  • DataLabel (String): the user editable name of this object, it is an arbitrary UTF8 string.

Hidden properties Data

  • Data (hidden)Proxy (PythonObject): a custom class associated with this object. This only exists for the Python version. See Scripting.
  • Data (hidden)Shape (PartShape): a Part TopoShape class associated with this object.
  • Data (hidden)Label2 (String): a longer, user editable description of this object, it is an arbitrary UTF8 string that may include newlines. By default, it is an empty string "".
  • Data (hidden)Expression Engine (ExpressionEngine): a list of expressions. By default, it is empty [].
  • Data (hidden)Visibility (Bool): whether to display the object or not.

View

Most objects in FreeCAD have what is called a "viewprovider", which is a class that defines the visual appearance of the object in the 3D view, and in the tree view. The default viewprovider of Part Feature objects defines the following properties. Scripted objects that are derived from Part Feature will have access to these properties as well.

Base

  • View (hidden)Proxy (PythonObject): a custom viewprovider class associated with this object. This only exists for the Python version. See Scripting.

Display Options

  • ViewBounding Box (Bool): if it is true, the object will show the bounding box in the 3D view.
  • ViewDisplay Mode (Enumeration): Flat Lines (regular visualization), Shaded (no edges), Wireframe (no faces), Points (only vertices).
  • ViewShow In Tree (Bool): it defaults to true, in which case the object will appear in the tree view; otherwise, the object will be hidden in the tree view. Once an object in the tree is invisible, you can see it again by opening the context menu over the name of the document (right-click), and selecting CheckBoxTrue.svg Show hidden items. Then the hidden item can be chosen and ViewShow In Tree can be switched back to true.
  • ViewVisibility (Bool): if it is true, the object appears in the 3D view; otherwise it is invisible. By default this property can be toggled on and off by pressing the Space bar in the keyboard.

Object style

  • ViewAngular Deflection (Angle): it is a companion to ViewDeviation. It is another way to specify how finely to generate the mesh for rendering on screen or when exporting. The default value is 28.5 degrees, or 0.5 radians. This is the maximum value, the smaller the value the smoother the appearance will be in the 3D view, and the finer the mesh that will be exported.
  • ViewDeviation (FloatConstraint): it is a companion to ViewAngular Deflection. It is another way to specify how finely to generate the mesh for rendering on screen or when exporting. The default value is 0.5%. This is the maximum value, the smaller the value the smoother the appearance will be in the 3D view, and the finer the mesh that will be exported.
  • View (hidden)Diffuse Color (ColorList): it is a list of RGB tuples defining colors, similar to ViewShape Color. It defaults to a list of one [(0.8, 0.8, 0.8)].

The deviation is a value in percentage that is related to the dimensions in millimeters of the bounding box of the object. The deviation in millimeters can be calculated as follows:

deviation_in_mm = (w + h + d)/3 * deviation/100

where w, h, d are the bounding box dimensions.

  • ViewDraw Style (Enumeration): Solid (default), Dashed, Dotted, Dashdot; defines the style of the edges in the 3D view.
  • ViewLighting (Enumeration): Two side (default), One side; the illumination comes from two sides or one side in the 3D view.
  • ViewLine Color (Color): a tuple of three floating point RGB values (r,g,b) to define the color of the edges in the 3D view; by default it is (0.09, 0.09, 0.09), which is displayed as [25,25,25] on base 255, almost black .
  • View (hidden)Line Color Array (ColorList): it is a list of RGB tuples defining colors, similar to ViewLine Color. It defaults to a list of one [(0.09, 0.09, 0.09)].
  • View (hidden)Line Material (Material): an App Material associated with the edges in this object. By default it is empty.
  • ViewLine Width (FloatConstraint): a float that determines the width in pixels of the edges in the 3D view. It defaults to 2.0.
  • ViewPoint Color (Color): similar to ViewLine Color, defines the color of the vertices.
  • View (hidden)Point Color Array (ColorList): it is a list of RGB tuples defining colors, similar to ViewPoint Color. It defaults to a list of one [(0.09, 0.09, 0.09)].
  • View (hidden)Point Material (Material): an App Material associated with the vertices in this object. By default it is empty.
  • ViewPoint Size (FloatConstraint): similar to ViewLine Width, defines the size of the vertices.
  • ViewShape Color (Color): similar to ViewLine Color, defines the color of the faces. It defaults to (0.8, 0.8, 0.8), which is displayed as [204, 204, 204] on base 255, a light gray.
  • View (hidden)Shape Material (Material): an App Material associated with this object. By default it is empty.
  • ViewTransparency (Percent): an integer from 0 to 100 (a percentage) that determines the level of transparency of the faces in the 3D view. A value of 100 indicates completely invisible faces; the faces are invisible but they can still be picked as long as ViewSelectable is true.

Selection

  • ViewOn Top When Selected (Enumeration): it controls the way in which the selection occurs in the 3D view if the object has a Shape, and there are many objects partially covered by others. It defaults to Disabled, meaning that no special highlighting will occur; Enabled means that the object will appear on top of any other object when selected; Object means that the object will appear on top only if the entire object is selected in the tree view; Element means that the object will appear on top only if a subelement (vertex, edge, face) is selected in the 3D view.
  • ViewSelectable (Bool): if it is true, the object can be picked with the pointer in the 3D view. Otherwise, the object cannot be selected until this option is set to true.
  • ViewSelection Style (Enumeration): it controls the way the object is highlighted. If it is Shape, the entire shape (vertices, edges, and faces) will be highlighted in the 3D view; if it is BoundBox a bounding box will appear surrounding the object and will be highlighted.

Deviation value

View property Deviation.svg

Deflection parameters of BRepMesh_IncrementalMesh algorithm; d < linear deflection, α < angular deflection.


See the forum thread, Deviation and Angular deflection.

Scripting

See also: FreeCAD Scripting Basics, and scripted objects.

A Part Feature is created with the addObject() method of the document.

import FreeCAD as App

doc = App.newDocument()
obj = App.ActiveDocument.addObject("Part::Feature", "Name")
obj.Label = "Custom label"

This basic Part::Feature doesn't have a Proxy object so it can't be fully used for sub-classing.

Therefore, for Python subclassing, you should create the Part::FeaturePython object.

import FreeCAD as App

doc = App.newDocument()
obj = App.ActiveDocument.addObject("Part::FeaturePython", "Name")
obj.Label = "Custom label"

Name

See also: Object name, for more information on the properties of the Name.

The addObject function has two basic string arguments.

  • The first argument indicates the type of object, in this case, "Part::FeaturePython".
  • The second argument is a string that defines the Name attribute. If it is not provided, it defaults to the same name as the class, that is, "Part__FeaturePython". The Name can only include simple alphanumeric characters, and the underscore, [_0-9a-zA-Z]. If other symbols are given, these will be converted to underscores; for example, "A+B:C*" is converted to "A_B_C_".

Label

If desired, the Label attribute can be changed to a more meaningful text.

  • The Label can accept any UTF8 string, including accents and spaces. Since the tree view displays the Label, it is a good practice to change the Label to a more descriptive string.
  • By default the Label is unique, just like the Name. However, this behavior can be changed in the preferences editor, Edit → Preferences → General → Document → Allow duplicate object labels in one document. This means that in general the Label may be repeated in the same document; when testing for a specific element the user should rely on the Name rather than on the Label.

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