AEC DevBlog（Revit 二次开发）- 使用 Revit API 选取三维点

原文链接： Picking 3D points using Revit API

作为 Revit 二次开发人员，我们很熟悉如何使用 Selection.PickPoint() 在二维平面上选取一个点。由于 Revit API 并不直接支持在三维坐标系中选取一个点，我们需要采用稍微复杂一点儿的方法来实现：
1. 首先借助 View.SketchPlane 属性设置当前工作平面；
2. 然后使用 Selection.PickPoint() 在当前工作平面上选取点

代码如下：

[Autodesk.Revit.Attributes.Transaction(Autodesk.Revit.Attributes.TransactionMode.Manual)]
public class Command : IExternalCommand
{     
	public Autodesk.Revit.UI.Result Execute(
		ExternalCommandData commandData,
		ref string message, 
		Autodesk.Revit.DB.ElementSet elements)
	{
		UIApplication uiapp = commandData.Application;
		UIDocument uidoc = uiapp.ActiveUIDocument;
		Application app = uiapp.Application;
		Document doc = uidoc.Document;

		XYZ point_in_3d;

		if (SetWorkPlaneAndPickObject(uidoc, out point_in_3d))
		{
			TaskDialog.Show("3D Point Selected",
				"3D point picked on the plane"
				+ " defined by the selected face: "
				+ "X: " + point_in_3d.X.ToString()
				+ ", Y: " + point_in_3d.Y.ToString()
				+ ", Z: " + point_in_3d.Z.ToString());

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

	/// 

	/// 返回一个三维坐标系中的点
	//  用户首先被要求选取某个元素的一个面（工作平面），然后用户在这个面上选取一个点
	/// 
	public bool SetWorkPlaneAndPickObject(
		UIDocument uidoc,
		out XYZ point_in_3d)
	{
		point_in_3d = null;
		Document doc = uidoc.Document;

		Reference r = uidoc.Selection.PickObject(
			Autodesk.Revit.UI.Selection.ObjectType.Face,
			"Please select a planar face to define work plane");
		Element e = doc.GetElement(r.ElementId); 
		if (null != e)
		{
			PlanarFace face = e.GetGeometryObjectFromReference(r)
			as PlanarFace;

			GeometryElement geoEle = e.get_Geometry(new Options());
			Transform transform = null;

			// 译者注：这段代码应该是基于 Revit 2012。在 Revit 2013 中，geoEle 本身就实现了 IEnumerable 接口，所以直接使用 geoEle 遍历即可
			foreach (GeometryObject gObj in geoEle.Objects)
			{
				GeometryInstance gInst = gObj as GeometryInstance;
				if (null != gInst)
				{
					transform = gInst.Transform;
				}
			}

			if (face != null)
			{
				Plane plane = null;

				// 译者注：这个 transform 很关键。它是表示元素自身的坐标系和当前文档的坐标系是否有差异。
				// 因为面的法线向量和面的原点的值都是基于元素自身的坐标系的。如果元素自身的坐标系和当前文档的坐标系有差异，则我们必须使用
				// 坐标系差异(transform)来将面的法线向量和面的原点的值转换成基于当前文档坐标系的值。
				if (null != transform)
				{
					plane = new Plane(transform.OfVector(face.Normal), transform.OfPoint(face.Origin));
				}
				else
				{
					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)
				{
				}

				// 译者注：回滚事务意味着之前创建的草图平面(SketchPlane)也自动被删除了
				t.RollBack();
			}
		}
		return null != point_in_3d;
	}