From: Oliver Burghard <OliverBurghard@...>
Date: 2008-11-30T10:08:43+09:00
Subject: Re: rmagick and circles

Yes, x_0 and y_0 are the coordinates of the center of the circle.


I am glad if I could help you. :)

Oliver


Am Sonntag, den 30.11.2008, 08:35 +0900 schrieb shawn bright:
> Thanks much
> tinkered around with my numbers in your formula, and it worked.
> 
> shawn
> 
> On Sat, Nov 29, 2008 at 2:48 PM, shawn bright <nephish@gmail.com> wrote:
> > This is great, thanks Oliver.
> > One question,
> >
> > what is meant by x_0 and y_0, are those the plot points for the center
> > of the graph?
> > thanks.
> > shawn
> >
> > On Sat, Nov 29, 2008 at 2:34 PM, Oliver Burghard <OliverBurghard@web.de> wrote:
> >> Hey,
> >>
> >> I am not sure what you want. If you only want one point it is easy:
> >>
> >> x = x_0 + radius * Math.cos(angle * 2.0 * Math::PI / 360.0)
> >> y = y_0 + radius * Math.sin(angle * 2.0 * Math::PI / 360.0)
> >>
> >> This is for the angle in degrees. Like this you can get any point on the
> >> circle. Now if you want to get the points of an arc you could just
> >> increase the angle a bit at a time and plot the points. But that would
> >> not be a very nice circle and would be slow.
> >>
> >> An option would be to get a starting point with the formula above and
> >> then iterate with x**2 + y**2 = r**2. For example in the first part of
> >> the circle between 0 and 45 degrees y is growing faster than x.
> >>
> >> You would start with an y and increase it once by one.
> >> ( leave away the translation for easiness )
> >>
> >> y' <- y + 1
> >> x' <- sqrt( r**2 - (y+1)**2 ) = sqrt( r**2 - y**2 -2*y - 1)
> >>        = sqrt( x**2 - 2 * y - 1)
> >>
> >> Hope it gives some ideas.
> >>
> >> Oliver
> >>
> >> Am Sonntag, den 30.11.2008, 04:45 +0900 schrieb shawn bright:
> >>> Hey there all,
> >>>
> >>> I am using RMagick to draw some circles.
> >>> what i need though is a math formula to give me a pair of plot points
> >>> for an angle.
> >>>
> >>> Say a circle is 40 x 40 on a sheet of graph paper.
> >>> this would put the center of the circle at x=20, y=20
> >>> and it would make the radius = 20.
> >>>
> >>> now, i need to be able to pass in a number like say, 20 degrees and
> >>> return the x and y plots of this on the circle.
> >>>
> >>> i know, more a math problem than ruby, but i could use any suggestions.
> >>>
> >>> thanks,
> >>> shawn
> >>>
> >>
> >>
> >>
> >
> >
>