Leaderboard

The geometric center (a.k.a. centroid) of an open polyline is deteremined by summing the length of each line segment times the coordinates of the midpoint of the respective segment. The result is then divided by the total length of the polyline. It is NOT the average of the point locations. ; Calculates the centroid for an open lwpolyline ; lrm 8/9/2025 (defun c:pl_centroid (/ ss pt_lst sum_x sum_y sum_d n i d mid_pt centroid) (setq ss (entget (car (Entsel "\nSelect Open Polyline"))) pt_lst (mapcar 'cdr (vl-remove-if-not '(lambda (x) (= (car x) 10)) ss) ) ) (setq sum_x 0 sum_y 0 sum_d 0.0 n (length pt_lst) i 0 ) (while (<= i (- n 2)) (setq d (distance (nth i pt_lst) (nth (+ i 1) pt_lst))) (setq mid_pt (mapcar '/ (mapcar '+ (nth i pt_lst) (nth (+ i 1) pt_lst)) '(2 2 2) ) ) (setq sum_x (+ sum_x (* (car mid_pt) d)) sum_y (+ sum_y (* (cadr mid_pt) d)) sum_d (+ d sum_d) i (+ i 1) ) ) (setq centroid (list (/ sum_x sum_d) (/ sum_y sum_d) ) ) (princ "\n Centroid at: ") (princ centroid) (command "_point" "_non" centroid) (princ) )