Re: ellipse code

["Chris Cheatham" <chris@xxxxxxxxxxxxxxxxxx>]

Again, thanks everyone. The more I ponder this, seems the better way to do
it (my project anyway) is as a plot, esp considering ts adding the # of
plots soon. I've got a good head start thanks to those who wrote. I'll pass
along what I come up with.

Best,
Chris
----- Original Message ----- 
From: "Alex Matulich" <alex@xxxxxxxxxxxxxx>
To: <omega-list@xxxxxxxxxx>
Sent: Monday, January 24, 2005 8:16 PM
Subject: Re: ellipse code


> >Anyone have any code to draw ellipses (really hexagons or octagons or
> >bleep-a-gons) that they would be willing to share?
>
> For an ellipse with horizontal axis 2a and vertical axis 2b, the
> radius r from the center at an angle theta from horizontal is
>
> ct = cos(theta)
> st = sin(theta)
> r = SquareRoot(b*b*a*a / (b*b*ct*ct + a*a*st*st))
>
> Then the x and y coordinates to plot are simply
>
> x = x0 + r*ct
> y = y0 + r*st
>
> where x0 and y0 are the origin.
>
> So, we can use trendlines to plot an ellipse having an axis of 2a bars
> horizontally and 2b price units vertically.  The downside is that you
> can't draw trendlines on future dates, so all points on the ellipse
> would have to exist on historical bars, not future bars.  A function to
> plot an ellipse might look something like this (untested):
>
> ===================================================================
> {function ellipse - untested}
> inputs: bars_ago(NumericSimple),    {bars ago for center of ellipse}
>         centerprice(NumericSimple), {price for center of ellipse}
>         a(NumericSimple),           {half of horizontal axis in bars}
>         b(NumericSimple),           {half of vertical axis in bars}
>         anglestep(NumericSimple);   {ellipse angle step (divides into
360)}
>
> var: theta(0), r(0), ct(0), st(0), xl(0),yl(0), x(0), y(0), TL(0);
>
> xl = bars_ago+a;
> yl = centerprice;
> for theta = anglestep to 360 begin
>    ct = cosine(theta);
>    st = sine(theta);
>    r = SquareRoot(b*b*a*a / (b*b*ct*ct + a*a*st*st));
>    x = date(int(bars_ago + 0.5 + r*ct));
>    y = centerprice + r*st;
>    TL = TL_New(date(xl),time(xl),yl,date(x),time(x),y);
>    xl = x;
>    yl = y;
>    theta = theta+anglestep-1; {force theta increment by anglestep each
loop}
> end;
> ===================================================================
>
> -Alex
>