Creating a Curved Beam

Here is a solution from my colleague Joe Ye on how to create a curved beam. This is also the first and so far only Building Coder sample that demonstrates the use of the Revit API DoubleArray and NurbSpline classes.

Question: I am creating curved beams using NURBS. When the spline in parallel to the XY plane, all works well:

When the curve is lying in the YZ or XZ plane, however, the resulting beam is straight:

How can I create the correct curved beam in all orientations?

Answer: This was actually a known issue in Revit 2009, and has been fixed in Revit 2010. I tested creating a nurbs-defined curved beam in the XZ plane in 2010 and it works well. Here is the resulting shape in front view:

This is the code of the Execute method used to create this beam, using a set of points in the XZ plane:

Application app = commandData.Application;
Document doc = app.ActiveDocument;
 
Level level = doc.ActiveView.Level;
 
FamilySymbol symbol = null;
 
string path = "C:/Documents and Settings"
  + "/All Users/Application Data/Autodesk"
  + "/RST 2009/Metric Library/Structural"
  + "/Framing/Steel/";
 
string family = "M_WWF-Welded Wide Flange";
 
string ext = ".rfa";
 
string filename = path + family + ext;
 
string symbolName = "WWF600x460";
 
if ( doc.LoadFamilySymbol( filename, symbolName, out symbol ) )
{
  Curve c = CreateNurbSpline( app );
 
  FamilyInstance inst 
    = doc.Create.NewFamilyInstance( 
      c, symbol, level, StructuralType.Beam );
 
  return IExternalCommand.Result.Succeeded;
}
else
{
  message = "Couldn't load " + filename;
  return IExternalCommand.Result.Failed;
}

The important step is the call to the CreateNurbSpline method, which generates the required input curve from a set of hard-coded points. Here is the definition of that method:

NurbSpline CreateNurbSpline( Application app )
{
  XYZArray ctrPoints = app.Create.NewXYZArray();
 
  XYZ xyz1 = new XYZ( -41.8 * 1, 0, -9.02 * 1 );
  XYZ xyz2 = new XYZ( -9.2 * 2, 0, 0.82 * 50 );
  XYZ xyz3 = new XYZ( 9.2 * 2, 0, -0.82 * 50 );
  XYZ xyz4 = new XYZ( 41.8 * 1, 0, 9.02 * 1 );
 
  ctrPoints.Append( xyz1 ); 
  ctrPoints.Append( xyz2 ); 
  ctrPoints.Append( xyz3 );
  ctrPoints.Append( xyz4 );
 
  DoubleArray weights = new DoubleArray();
 
  double w1 = 1, w2 = 1, w3 = 1, w4 = 1;
 
  weights.Append( ref w1 ); 
  weights.Append( ref w2 ); 
  weights.Append( ref w3 );
  weights.Append( ref w4 );
 
  DoubleArray knots = new DoubleArray();
 
  double k0 = 0, k1 = 0, k2 = 0, k3 = 0, 
    k4 = 34.425128, k5 = 34.425128, 
    k6 = 34.425128, k7 = 34.425128;
 
  knots.Append( ref k0 ); 
  knots.Append( ref k1 ); 
  knots.Append( ref k2 ); 
  knots.Append( ref k3 );
  knots.Append( ref k4 ); 
  knots.Append( ref k5 ); 
  knots.Append( ref k6 );
  knots.Append( ref k7 );
 
  NurbSpline detailNurbSpline 
    = app.Create.NewNurbSpline( 
    ctrPoints, weights, knots, 3, false, true );
 
  return detailNurbSpline;
}

Many thanks to Joe for providing this solution!