AutoCAD 2007/2008/2009

AutoCAD 2007/2008/2009

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New Member
Illustartor_101
Posts: 1
Registered: ‎08-06-2008
Message 1 of 8 (1,658 Views)

Degenerate Geometry

1658 Views, 7 Replies
08-06-2008 11:19 AM
I use AutoCAD to do 3D Tech Illustration. I don’t spend a lot of time creating 3D models, instead I keep them simple. I save them as “flat” views and finish them off using trimetrics with some artistic flare. Consequently I end up working with and editing a lot of ellipses. The problem I constantly have is when I try to modify properties to change the start and stop points and close an open ellipse (start 0, end 360) I get a “degenerate geometry” error message. The weird thing is that I don’t always get the error message. Sometimes I can close the ellipse and sometimes I can’t.

Does anyone know what is meant by “degenerate geometry”, and does anyone know how to correct it???
*Expert Elite*
drjohn
Posts: 1,762
Registered: ‎03-01-2006
Message 2 of 8 (1,658 Views)

Re: Degenerate Geometry

08-06-2008 11:24 AM in reply to: Illustartor_101
Degeneracies arise in geometric data due to the special position of two or more objects. Well-known examples in three-dimensions include co-planar, co-linear, or co-located points, and its even possible for two line segments to intersect exactly in three dimensions. More diabolical cases include those where two line segments in special position overlap without sharing an end point, or even having the decency to be co-linear. While seemingly unlikely (mathematically) degenerate data is common in the real world, and especially the somewhat quantized world of computational geometry.

Source: http://people.nas.nasa.gov/~aftosmis/cart3d/degen_ex.html

(Google is your friend :-) )

From this I am assuming that you have geometry that is crossing or intersecting incorrectly.
New Member
Illustrator_101
Posts: 2
Registered: ‎08-06-2008
Message 3 of 8 (1,658 Views)

Re: Degenerate Geometry

08-07-2008 11:58 AM in reply to: Illustartor_101
Thanks for the reply and link, but to be honest I am now more confused than ever???????????
Distinguished Contributor
zzz144
Posts: 184
Registered: ‎06-12-2008
Message 4 of 8 (1,658 Views)

Re: Degenerate Geometry

08-07-2008 12:07 PM in reply to: Illustartor_101
confused.... lol me too

try setting you closing angle to 359.9999 degrees

what do you mean i finish w/ trimetrics with some artistic flare
Distinguished Contributor
C O Jones
Posts: 1,635
Registered: ‎01-20-2006
Message 5 of 8 (1,658 Views)

Re: Degenerate Geometry

08-07-2008 01:14 PM in reply to: Illustartor_101
http://en.wikipedia.org/wiki/Trimetric_projection
New Member
Illustrator_101
Posts: 2
Registered: ‎08-06-2008
Message 6 of 8 (1,658 Views)

Re: Degenerate Geometry

08-11-2008 01:45 PM in reply to: Illustartor_101
"what do you mean i finish w/ trimetrics with some artistic flare"

Unlike isometric projection, trimetric projection uses 3 different ellipses. Once I have a 3D model roughed in, I set it to my Trimetric view angles and save it out as a flat view. Then I finish the detail pretty much the same way I use to do it on a drafting board. I hope I am not dating myself too much. But for the type of work I do it is much quicker than trying to do all that detail on a 3D model……..
*Dilip Damle
Message 7 of 8 (1,658 Views)

Re: Degenerate Geometry

08-16-2008 01:05 AM in reply to: Illustartor_101
On Wed, 06 Aug 2008 23:49:29 +0530, Illustartor_101 wrote:

> I use AutoCAD to do 3D Tech Illustration. I don’t spend a lot of time creating 3D models, instead I keep them simple. I save them as “flat” views and finish them off using trimetrics with some artistic flare. Consequently I end up working with and editing a lot of ellipses. The problem I constantly have is when I try to modify properties to change the start and stop points and close an open ellipse (start 0, end 360) I get a “degenerate geometry” error message.


In Autocad you can not edit an ARC so that it becomes a 360 degree ARC or a full circle
the same thing is with Elliptical ARCS you can not have then 360 degree.


> The weird thing is that I don’t always get the error message. Sometimes I can close the ellipse and sometimes I can’t.

I do not think you can ever close the ellipse

Whenever you feel you can close it please check it might actually be Two separate Elliptical ARCS
and not One

> Does anyone know what is meant by “degenerate geometry”, and does anyone know how to correct it???
>


--
rgds
Dilip Damle
--------------------------------------------------------------------
Life will be much easier if we just have a printout of
all the commands that exist in Autocad kept handy.
New Member
mikelynch
Posts: 1
Registered: ‎11-03-2012
Message 8 of 8 (1,408 Views)

Re: Degenerate Geometry

11-03-2012 02:51 PM in reply to: Illustartor_101

If you change the endangle to 359, then the start to 0, then the end back to 360 you can close the ellipse...

 

regards

 

Mike

 

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