From: Xin Zheng <crazygecko@...>
Date: 2008-01-16T21:26:23+09:00
Subject: Re: spatial search & search radius circumference with Geokit

Andre Lewis wrote:
> Hi Xin, here is an example of plotting a circle (from centerpoint and 
> radius) in Javascript : 
> http://www.ovationmarketing.com/GMaps/MapCircle.asp . You can find other 
> examples out there too by googling around.


Thanks for the link Andre. This is a lot easier to understand than the 
xmaps (http://xmaps.busmonster.com/) code I was looking at.


I have now converted this into Ruby. Most of the time the circle polygon 
I draw matches with the results returned from Geokit. But sometimes 
results fall outside of it.

Here's my code:
      def circle_points(center_x, center_y, radius, quality = 3)

        points = []
        radians = Math::PI / 180

        0.step(360, quality) do |i|
          x = center_x + (radius * Math.cos(i * radians))
          y = center_y + (radius * Math.sin(i * radians))
          points << [x,y]
        end
        points
      end

radius = miles * (360 / 24901.463)
where 24901.463 is the circumference of Earth in miles I'm using. I took 
this from Wikipedia.

Are you using the same algorithm?

Are you using the same circumference?

Thanks for helping!

Xin




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