Revit API选择三维视图上一点

start
[TransactionAttribute(Autodesk.Revit.Attributes.TransactionMode.Manual)]
public class cmdPickPointIn3d : IExternalCommand
{
public Result Execute(ExternalCommandData commandData, ref string messages, ElementSet elements)
{
UIApplication app = commandData.Application;
Document doc = app.ActiveUIDocument.Document;

XYZ point_in_3d;

if (PickFaceSetWorkPlaneAndPickPoint( app.ActiveUIDocument, out point_in_3d))
{
TaskDialog.Show("3D Point Selected",
"3D point picked on the plane"
+ " defined by the selected face: "
+ PointString(point_in_3d));

return Result.Succeeded;
}
else
{
messages = "3D point selection failed";
return Result.Failed;
}

return Result.Succeeded;
}
string PointString(XYZ p)
{
return string.Format("({0},{1},{2})",
RealString(p.X),
RealString(p.Y),
RealString(p.Z));
}
string PointString(UV p)
{
return string.Format("({0},{1})",
RealString(p.U),
RealString(p.V));
}
string RealString(double a)
{
return a.ToString("0.##");
}
bool PickFaceSetWorkPlaneAndPickPoint(UIDocument uidoc, out XYZ point_in_3d)
{
point_in_3d = null;

Document doc = uidoc.Document;

Reference r = uidoc.Selection.PickObject(
ObjectType.Face,
"Please select a planar face to define work plane");

Element e = doc.get_Element(r.ElementId);

if (null != e)
{
PlanarFace face
= e.GetGeometryObjectFromReference(r)
as PlanarFace;

if (face != null)
{
Plane plane = new Plane(
face.Normal, face.Origin);

Transaction t = new Transaction(doc);

t.Start("Temporarily set work plane"
+ " to pick point in 3D");

SketchPlane sp = doc.Create.NewSketchPlane(
plane);

uidoc.ActiveView.SketchPlane = sp;
uidoc.ActiveView.ShowActiveWorkPlane();

try
{
point_in_3d = uidoc.Selection.PickPoint(
"Please pick a point on the plane"
+ " defined by the selected face");
}
catch (OperationCanceledException)
{
}

t.RollBack();
}
}
return null != point_in_3d;
}
}url：http://greatverve.cnblogs.com/p/pick-a-point-in-3d.html