Surface Sections

    From FreeCAD Documentation
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    Surface Sections.svg Surface Sections

    Menu location
    Surface → Sections
    Default shortcut
    Introduced in version
    See also


    Surface Sections.svg Surface Sections is used to create a surface from edges that represent transversal sections of a surface.

    Surface Sections edges example.png Surface Sections example.png

    Left: control edges (transversal sections). Right: surface produced from these edges.


    1. Make sure you have at lease two edges or curves in space. For example, these can be created with tools of the Workbench Draft.svg Draft Workbench or the Workbench Sketcher.svg Sketcher.
    2. Press the Surface Sections.svg Surface sections button.
    3. Press Add edge.
    4. Use the pointer to pick the desired edges in the 3D view; a preview of the final shape will be shown after selecting two valid edges.
    5. Press OK to complete the operation.


    • Add edge: press once to start picking edges in the 3D view. Individual lines such as Draft BSpline.svg Draft BSplines and Sketcher CreateBSpline.svg Sketcher BSplines can be chosen, as well as any edge from solid objects, like those of PartDesign Body.svg PartDesign Bodies and Part Primitives.svg Part Primitives.
    • Remove edge: press once to start picking edges in the 3D view; these must be edges that were previously picked with Add edge.
    • Right mouse button: open the context menu and select Remove, or press Del in the keyboard, to remove the currently selected edge in the list.
    • Drag: drag the currently selected element in the list in order to change the order in which it will be processed; the list is processed from top to bottom.
    • Press Cancel or Esc to abort the current operation.


    A Surface Sections (Surface::Sections class) is derived from the basic Part Feature (Part::Feature class, through the Part::Spline subclass), therefore it shares all the latter's properties.

    In addition to the properties described in Part Feature, the Surface Sections has the following properties in the property editor.



    • DataNSections (LinkSubList): a list of edges that will be used to build the surface.



    • ViewControl Points (Bool): it defaults to false; if set to true, it will show an overlay with the control points of the surface.

    Twisting of the surface

    The shape of the surface depends on the direction of the chosen edges; if edges are selected and the result is a surface that "twists" on itself, one of the edges may need its list of vertices in the reverse order. See the information in Surface GeomFillSurface.svg GeomFillSurface for a more complete explanation.

    Surface twisting example smooth.png Surface twisting example twisted.png


    See also: FreeCAD Scripting Basics.

    The Surface Sections tool can be used in macros and from the Python console by adding the Surface::Sections object.

    • The edges to be used to define the surface must be assigned as a LinkSubList to the NSections property of the object.
    • All objects with edges need to be computed before they can be used as input for the properties of the Sections object.
    import FreeCAD as App
    import Draft
    doc = App.newDocument()
    pl1 = App.Placement()
    obj1 = Draft.make_circle(50, placement=pl1, face=False, startangle=0, endangle=180)
    pl2 = App.Placement(App.Vector(0, 0, 25), App.Rotation())
    obj2 = Draft.make_circle(30, placement=pl2, face=False, startangle=0, endangle=180)
    points3 = [App.Vector(18, -10, 50),
               App.Vector(12, 10, 50),
               App.Vector(-12, 10, 50),
               App.Vector(-18, -10, 50)]
    obj3 = Draft.make_bspline(points3)
    points4 = [App.Vector(15, -20, 100),
               App.Vector(0, 6, 100),
               App.Vector(-15, -20, 100)]
    obj4 = Draft.make_bspline(points4)
    surf = doc.addObject("Surface::Sections", "Surface")
    surf.NSections = [(obj1, "Edge1"),
                      (obj2, "Edge1"),
                      (obj3, "Edge1"),
                      (obj4, "Edge1")]