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# 3D Polyline to 2D Polyline with different Z

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Hello, I have a city map with lots of building plans, most of them are 3D polylines and all of them has different Z values, according to their heights. I want to make a 3D model out of it by simply extruding them. But those 3D polylines have vertexes on different elevations. Is there a way to find a geometric center for each of those 3D polylines and flatten them into 2D polylines that has the Z value of that geometric center. So that I would have 2D polylines with different Z values. (I don't want to flatten everything to Z=0) Thanks in advance!

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Hi  tolgydd . For better understanding, and  maybe get further help, please upload such sample.dwg

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Perhaps simplest is get co-ords of 3dpoly, take average of z, then make a new normal pline but with ELEV set at the Z value THICKNESS can be height of building.

If you want a top look into "pface"

```; this works for 3dpoly and bricscad
; co-ords by by lee-mac
; 3dpoly to 2dpoly with thickness
; by Alanh Sep 2020

(defun c:test ( / e lst v x tot x z)
(while (setq e (car (entsel "\nSelect polyline: ")))
(if  (= "POLYLINE" (cdr (assoc 0 (setq x (entget e)))))
(progn
(setq lst '())
(setq v (entnext e)
x (entget  v)
)
(while (= "VERTEX" (cdr (assoc 0 x)))
(setq lst (cons (cdr (assoc 10 x)) lst)
v (entnext v)
x (entget  v)
)
)

(setq tot 0.0 x (length lst))

(repeat (length lst)
(setq tot (+ (nth 2 (nth (setq x (- x 1)) lst)) tot))
)

(setvar 'thickness (getreal "\nEnter building height "))
(entmakex (append (list (cons 0 "LWPOLYLINE")
(cons 100 "AcDbEntity")
(cons 100 "AcDbPolyline")
(cons 90 (length lst))
(cons 70 1))
(mapcar (function (lambda (p) (cons 10 p))) lst)))

(setq z (atof (rtos (length lst) 2 3)))
(command "move" "last" "" "0,0,0" (list 0 0 (/ tot z)))

(setvar 'thickness 0.0)
)
(princ "\nThe selected object is not a 2d or 3D polyline.")
)

)
(princ)
)
(c:test)```

Edited by BIGAL

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