Getting the centroid of closed polyline

[csgohjmj]

Hi;
I am trying get the coordinates of the centroid of a closed polyline but do not have any idea at all. Is there any lisp routine whereby the coordinate can be obtained? Any help is much appreciated. Thanks.

csgoh
9-7-04

[David.Hoole]

Hi csgoh

Use the REGION command to convert the Polyline to a Region, then use the MASSPROP command to list its physical properties, which include the centroid.

[csgohjmj]

Hi David,
Thanks for the tip but using massprop only lists out the properties. But I need to get the centroid coordinates in order to insert text at this point and how can I do this?
Thanks.

csgoh

[David.Hoole]

Hi csgoh

Sorry, forgot we were in a programming forum! Try this:

(setq obj (vlax-ename->vla-object (car (entsel))))
(setq centroid (vlax-safearray->list (vlax-variant-value (vla-get-centroid obj))))

Hope I got the code window right! Fluffed it last time

[David.Hoole]

Hi csgoh

Looks like I fluffed the text window again . I may have to read the instructions

Thought you might find a practical example useful:

(defun c:get_centroid ( / ename obj centroid)
(setq ename (car (entsel "\nSelect polyline:")))
(command "region" ename "")
(setq ename (entlast))
(setq obj (vlax-ename->vla-object ename))
(setq centroid (vlax-safearray->list (vlax-variant-value (vla-get-centroid obj))))
(command "undo" "")
(command "text" "j" "mc" centroid 2.5 0.0 "CENTROID")
(princ)
)

[csgohjmj]

Dear David;
Thanks but the code that you have given is good for ACAD 2K & above. How about those older version like Autocad R14 version. I have tried using entget to retrieve the centroid but to no avail and I hope you could help me.

Thanks again.

csgoh
11-7-04

[csgohjmj]

Hi;
I have tried David's code on ACAD R14 and 2002 by entering the code at command line.
However it gives me an [error: null function in ACAD R14 and no function definition in ACAD 2002] when I key in these code [ (setq obj(vlax-ename->vla-object ename)) ].
Now what have I done wrong here? Is there anything else that I have to do in order to be able to use the vl/vla funtions? This is my first attempt to use the vl functions in autolisp and I hope to get some guidance on these.
Thanks.

csgoh

[Mike.Perry]

Hi

Try adding -

(vl-load-com)

at the beginning of David's routine ie

(vl-load-com)
(defun c:get_centroid ( / ename obj centroid)
....

Have a good one, Mike

[csgohjmj]

Thanks Mike but it does not work in ACAD R14. Guess ACAD R14 does not support vl functions. Seems that I have to save the massprop into a file and retrieve the centroid - a longer process as compared to ACAD 2002.
Thanks.

csgoh

[Mike.Perry]

Hi

For a little Visual LISP history regarding AutoCAD R14 check out the following links -

Visual LISP For AutoCAD R14

AutoCAD Customization Overview

History of AutoLISP

Have a good one, Mike