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  1. PO
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    <p>I have given up with the winding number code, it really has got me! If anyone does find the solution I would still be amazingly grateful. I am now trying with point in poly detection using the crossing number algorithm. I kept the pesudo code in the comments, again from softsurfer....</p> <pre><code>int cn_PnPoly( Point P, Building &amp; b, int n ) { int cn = 0; // the crossing number counter int rem = 0; vector&lt;float&gt;x; vector&lt;float&gt;y; x.swap(b.getX()); y.swap(b.getY()); //// loop through all edges of the polygon //for (int i=0; i&lt;n; i++) { // edge from V[i] to V[i+1] // if (((V[i].y &lt;= P.y) &amp;&amp; (V[i+1].y &gt; P.y)) // an upward crossing // || ((V[i].y &gt; P.y) &amp;&amp; (V[i+1].y &lt;= P.y))) { // a downward crossing // // compute the actual edge-ray intersect x-coordinate // float vt = (float)(P.y - V[i].y) / (V[i+1].y - V[i].y); // if (P.x &lt; V[i].x + vt * (V[i+1].x - V[i].x)) // P.x &lt; intersect // ++cn; // a valid crossing of y=P.y right of P.x // } //} //return (cn&amp;1); // 0 if even (out), and 1 if odd (in) // loop through all edges of the polygon for (int i=0; i&lt;n-1; i++) { // edge from V[i] to V[i+1] if (((y.at(i) &lt;= P.y) &amp;&amp; (y.at(i+1) &gt; P.y)) // an upward crossing || ((y.at(i) &gt; P.y) &amp;&amp; (y.at(i+1) &lt;= P.y))) { // a downward crossing // compute the actual edge-ray intersect x-coordinate float vt = (float)(P.y - y.at(i)) / (y.at(i+1) - y.at(i)); if (P.x &lt; x.at(i) + vt * (x.at(i+1) - x.at(i))) // P.x &lt; intersect ++cn; // a valid crossing of y=P.y right of P.x } } rem = cn % 1; return (rem); // 0 if even (out), and 1 if odd (in) } </code></pre> <p>Again this always returns zero, I am unsure why!?! Have I converted the algorithm incorrectly? Does it matter which direction the points are tested (i.e. clockwise, anti-clockwise)?</p>
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    1. POError, Implementing Winding Number Algorithm, (OpenGL, C++)
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    1. USbinarycreations
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    1. COAll I can say is that you should really try to understand the algorithm. Once you do, you'll be able to debug the code. It's just basic geometry + common sense, after all.
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