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Asked: 2026-05-22T11:30:41+00:00

I have been using this this oval function (that I found at Wikipedia http://en.wikipedia.org/wiki/Ellipse

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I have been using this this oval function (that I found at Wikipedia http://en.wikipedia.org/wiki/Ellipse) for plotting points in a layout. I have been laying things out with two to five points plotted around an oval without any problem. The function has a parameter called ‘steps’; the ‘steps’ parameter sets the quantity of points to plot around the oval.

Here’s the main problem: If ‘steps’ (the number of points to plot) is equal to the numbers 7, 11, 13 or 14, it breaks. It’s been a few years since I took trigonometry, so basically I am stuck.

Second minor issue: I had the code printing out all points, but when I copied/pasted and removed extraneous code to post here, it only prints out the last plotting point (not sure why).

<html>
<head>
<script type="text/javascript">
    var elipticalLayout=new Array();
    for (i=0; i <36; i++){
        elipticalLayout[i]=new Array(2);
    }

    /*
    * This functions returns an array containing the specified 
    *    number of 'steps' (points) to draw an ellipse.
    *
    * @param x {double} X coordinate
    * @param y {double} Y coordinate
    * @param a {double} Semimajor axis
    * @param b {double} Semiminor axis
    * @param angle {double} Angle of the ellipse
    *
    * Attribution: This function is from http://en.wikipedia.org/wiki/Ellipse
    */
    function calculateEllipticalLayout(x, y, a, b, angle, steps) {

      var points = [];

      // Angle is given by Degree Value
      var beta = -angle * (Math.PI / 180); //(Math.PI/180) converts Degree Value into Radians
      var sinbeta = Math.sin(beta);
      var cosbeta = Math.cos(beta);

      for (var i = 0; i < 360; i += 360 / steps) //{
        var alpha = i * (Math.PI / 180) ;
        var sinalpha = Math.sin(alpha);
        var cosalpha = Math.cos(alpha);

        var X = x + (a * cosalpha * cosbeta - b * sinalpha * sinbeta);
        var Y = y + (a * cosalpha * sinbeta + b * sinalpha * cosbeta);
        elipticalLayout[i/(360/steps)][0]=X;
        elipticalLayout[i/(360/steps)][1]=Y;
    }

    </script>
</head>
<body>
    <script type="text/javascript">

        calculateEllipticalLayout(300, 300, 245, 125,  15,    15);

        for (i=0; i<elipticalLayout.length; i++){
            document.write(i + ", " + elipticalLayout[i][0] + ", " + elipticalLayout[i][1] + "<br>");
        }
    </script>

</body>
</html>
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1 Answer

  1. Editorial Team

    You fill only steps number of elements in elipticalLayout.
    But trying to output 36 of them.

    This elipticalLayout[i/(360/steps)][0]=X; is wrong as will lead to “holes” in the sequence due to float to int rounding.

    You should have something like this:

    var n = 0;
for(...)
   elipticalLayout[n][0]=X;
   elipticalLayout[n][1]=Y;
   ++n;
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