Creating a Void to Cut Family Geometry

In a comment to “Calculating the glass in a door“, the question was posed:

“Let’s say I have a 7′ tall, full glass door. How complicated would it be to add constraints, or limits, to the area in which you want to calculate? Say I want to calculate the total are of glass between 2′ and 6′ (assuming the total glass area was greater than that).”

The place to start answering this question is with API code to create a void that eliminates the glass in the door below 2′. The image below was created with “Double-Glass 1.rfa”.


public void CreateExtrusionAndCutGlass()
    Document doc = this.ActiveUIDocument.Document;
    Autodesk.Revit.ApplicationServices.Application app = doc.Application;

    // Height of the void extrusion
    double height = 2;

    // Four points to define corners of the rectangle to extrude
    XYZ pnt1 = new XYZ(-10, -10, 0);
    XYZ pnt2 = new XYZ(10, -10, 0);
    XYZ pnt3 = new XYZ(10, 10, 0);
    XYZ pnt4 = new XYZ(-10, 10, 0);

    // Create the four lines of the rectangle
    // These are internal "Line" elements, not model lines or detail lines
    Line line1 = app.Create.NewLine(pnt1, pnt2, true);
    Line line2 = app.Create.NewLine(pnt2, pnt3, true);
    Line line3 = app.Create.NewLine(pnt3, pnt4, true);
    Line line4 = app.Create.NewLine(pnt4, pnt1, true);

    // Put these lines into a CurveArray
    CurveArray curveArray = new CurveArray();

    // Put this array into a CureArrArray (an array of CurveArrays)
    // Extrusion creation uses a CureArrArray so you can extrusion multiple loops 
    CurveArrArray curveArrayArray = new CurveArrArray();

    // Create a plane at the origin with a normal in the up direction
    XYZ planeNormal = XYZ.BasisZ;
    XYZ planeOrigin = XYZ.Zero;
    Plane plane = app.Create.NewPlane(planeNormal, planeOrigin);

    Extrusion extrusion = null;

    using (Transaction t = new Transaction(doc, "Create Extrusion"))
            // Create a sketch plane to be used for the extrusion
            SketchPlane sketchPlane = doc.FamilyCreate.NewSketchPlane(plane);
            // Create the extrusion. The "false" specifies that it will be a void
            extrusion = doc.FamilyCreate.NewExtrusion(false, curveArrayArray, sketchPlane, height);

    // Cut the other 3D elements with the new void using CombineElements and a CombinableElementArray
    CombinableElementArray ceArray = new CombinableElementArray();

    // Add the new void extrusion to the CombinableElementArray

    // Add all GenericForm elements with the Glass subcategory to a CombinableElementArray
    foreach (GenericForm genericForm in new FilteredElementCollector(doc).OfClass(typeof(GenericForm)).Cast<GenericForm>())
        Category category = genericForm.Subcategory;
        if (category != null && category.Name == "Glass")

    using (Transaction t = new Transaction(doc, "Combine Elements"))
            // Combine the elements so that the void will cut the solids
            GeomCombination geomCombination = doc.CombineElements(ceArray);

One thought on “Creating a Void to Cut Family Geometry

  1. […] Here are a few of my favourite posts from the Boost Your BIM site – check some of them out and using the method explained above, add them to your Revit application editor. Using 3D Section Box to set Plan View’s View Range, Divide Parts at Levels, Creating a Void to Cut Family Geometry. […]

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