private FamilyInstanceCreationData GetCreationData(Autodesk.Revit.DB.Curve curve, Autodesk.Revit.DB.XYZ upVector, Autodesk.Revit.DB.Level level, Autodesk.Revit.DB.Structure.StructuralType structuralType, Autodesk.Revit.DB.FamilySymbol symbol)
{
//calculate the desired rotation
//we do this by finding the angle between the z axis
//and vector between the start of the beam and the target point
//both projected onto the start plane of the beam.
var zAxis = new XYZ(0, 0, 1);
var yAxis = new XYZ(0, 1, 0);
//flatten the beam line onto the XZ plane
//using the start's z coordinate
var start = curve.GetEndPoint(0);
var end = curve.GetEndPoint(1);
var newEnd = new XYZ(end.X, end.Y, start.Z); //drop end point to plane
//catch the case where the end is directly above
//the start, creating a normal with zero length
//in that case, use the Z axis
XYZ planeNormal = newEnd.IsAlmostEqualTo(start) ? zAxis : (newEnd - start).Normalize();
double gamma = upVector.AngleOnPlaneTo(zAxis.IsAlmostEqualTo(planeNormal) ? yAxis : zAxis, planeNormal);
return(new FamilyInstanceCreationData(curve, symbol, level, structuralType)
{
RotateAngle = gamma
});
}