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POget points on an arc or oval in Android
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copied!<p>I'm trying to create something like the "Big Wheel" off of the price is right. Kinda like this:</p> <p><img src="https://i.stack.imgur.com/5JeN4.png" alt="big wheel"></p> <p>I've got the left oval, the right arc and the top and bottom posts done. Where I am lost at is how to create the inner lines without resorting to a bunch of complicated math. I figure that if I can get the points on my shapes somehow I can fairly easily make my lines this way. However, I am not finding anything in the Android SDK that gives me this. </p> <p>Is there any way to get the points of drawn objects in Android? If not, is there a simpler solution that I'm not seeing?</p> <p>Thanks in advance!</p> <p><strong>EDIT #1:</strong></p> <p>With the post below I took a whack at the math and I can't seem to get it to work :(</p> <p>This is what I have so far:</p> <pre><code> float a = (leftOval.bottom - leftOval.top) / 2; float b = (leftOval.right - leftOval.left) / 2; float x1 = (float) getXForOval(a, b, top + 50); float y1 = top + 50; float x2 = x1 + 50; float y2 = y1; Log.d("coords", "compute: " + getXForOval(a, b, top + 50) + ""); Log.d("coords", "leftOval.top: " + leftOval.top + ""); Log.d("coords", "leftOval.bottom: " + leftOval.bottom + ""); Log.d("coords", "leftOval.right: " + leftOval.right + ""); Log.d("coords", "leftOval.left: " + leftOval.left + ""); Log.d("coords", "a: " + a + ""); Log.d("coords", "b: " + b + ""); Log.d("coords", "x1: " + x1 + ""); Log.d("coords", "y1: " + y1 + ""); Log.d("coords", "x2: " + x2 + ""); Log.d("coords", "y2: " + y2 + ""); canvas.drawLine(x1, y1, x2, y2, paint); private double getXForOval(float a, float b, float y) { // sqrt ( a^2 * (1 - y^2 / b^2) ) // @formatter:off return Math.sqrt( Math.abs( Math.pow(a, 2) * ( 1 - ( Math.pow(y, 2) / Math.pow(b, 2) ) ) ) ); // @formatter:on } </code></pre> <p>But the X value is coming out way large. What am I doing wrong?</p> <pre><code>08-27 18:16:56.574: DEBUG/coords(2785): compute: 2743.647207641682 08-27 18:16:56.584: DEBUG/coords(2785): leftOval.top: 180.0 08-27 18:16:56.584: DEBUG/coords(2785): leftOval.bottom: 780.0 08-27 18:16:56.584: DEBUG/coords(2785): leftOval.right: 185.0 08-27 18:16:56.584: DEBUG/coords(2785): leftOval.left: 135.0 08-27 18:16:56.584: DEBUG/coords(2785): a: 300.0 08-27 18:16:56.584: DEBUG/coords(2785): b: 25.0 08-27 18:16:56.584: DEBUG/coords(2785): x1: 2743.6472 08-27 18:16:56.584: DEBUG/coords(2785): y1: 230.0 08-27 18:16:56.584: DEBUG/coords(2785): x2: 2793.6472 08-27 18:16:56.584: DEBUG/coords(2785): y2: 230.0 </code></pre>

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