Autocad 2018 - Select elements within a POLYLINE

select_within_polyline.lsp

; Script courtesy of wronzky @ http://ww3.cad.de/foren/ubb/Forum54/HTML/018135.shtml
; Use a polyline (supposedly only LWPOLYLINE) as a selector. Will select all items inside.
; If you have a Region, try to EXPLODE, QSELECT lines then JOIN to form a single POLYLINE
; Use BOUNDARY to create a new POLYLINE from an enclosed area.
; Follow the command with WBLOCK to write elements to a new file.
; Modified by joakimsk, tested on Autocad 2018 OS X

(defun c:lcp ( / ) ; lcp selects all elements crossing or is inside the polyline (Crossing Polygon)
  (sssetfirst nil (ssget "_CP" (vox-get-points (car (entsel "\nSelect 'Crossing Polygon' POLYLINE:")))))
)
(defun c:lwp ( / ) ; lwp selects all elements fully inside the polyline (Window Polygon)
  (sssetfirst nil (ssget "_WP" (vox-get-points (car (entsel "\nSelect 'Window Polygon' POLYLINE:")))))
)
(defun vox-get-points (ele) ; subroutine that remove all points that are outside the polyline area
  (mapcar 'cdr  (vl-remove-if '(lambda(x) (/= (car x) 10)) (entget ele)))
)