cutting up an oval into perimeter segments?

[Ethan R.]

I have an oval room that I measured around the perimeter as to door

placement .. now that I am back in my office, I am attempting to plot out

where the doors fall on the ellipse.

The oval is 85'w x 116'L

with breaks for Doors from 0 (being the bottom center quad of the ellipse)

as follows:

0 --> 38.5

13'4 --> 16'6

30'11 -->34'4

along the circumference of the ellipse / perimeter of the room

any ideas on how to plot this out?

thanks,

Ethan

[jan15]

The math for ellipses is pretty tough. See http://www.geom.umn.edu/docs/reference/CRC-formulas/node29.html

So I would probably approximate it iteratively with circular arcs.

To find a point 13'-4" = 160" = 13.33' from point P on the ellipse:

1. Draw a circle with center at P and radius 160.

2. Draw an arc (3 pt method) that approximates the elliptical arc between P and the intersection of the ellipse and the circle.

3. Check its arc length in ObjInfo

4. Adjust the arc's length with the Select tool till it equals 13.33'

5. If necessary, draw a new arc that more closely approximates the shape of the elliptical arc and repeat steps 3 and 4.

6. Repeat step 5 till you feel you're close enough.

[P Retondo]

quote:

---

Originally posted by jan15:

The math for ellipses is pretty tough.

---

NNA: here's a pretty good reason to consider including a way to divide a curved line into segments, as someone has requested recently. The math is tough, unless a computer can do it for us.

BTW, I wonder if your programmers have ever used the C++ library that MatLab provides. Makes this kind of thing relatively easy.

[ 02-27-2003, 01:55 AM: Message edited by: P Retondo ]

[Ethan R.]

Wow .. That is math I haven't calculated out since calculus in high school! Too much for me to figure out with the deadline at hand.

Instead, I am flipping over to AutoCAD and utilizing the measure & Divide commands - then re-importing back to Vworks

thanks for the help!

E

[jfmarch]

Your client's last name wouldn't be Bush would it?

[jan15]

The method I described above may sound complicated, but it's really very easy.

I tried it before writing it down. The first circular arc I drew looked more than close enough for any construction purpose. The whole procedure took about fifteen seconds in VectorWorks 8. It probably wouldn't take much more than a minute in version 10.

Note that the incredibly complex math on that web site also produces only an approximate value.