Re: select elements witch cut by the view

You can use a BoundingBoxIntersectsFilter.

BoundingBoxIntersectsFilter CutPlaneFilter = new BoundingBoxIntersectsFilter(_outline);

List<Element>  ElemsInCutPlane =

   new FilteredElementCollector(doc, ActiveView.Id)

      .WhereElementIsNotElementType()

      .WherePasses(CutPlaneFilter)

      .ToList<Element>();

where _outline is made from the points of a region in the cutplane , for instance the Crop Region