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--- code:uk_polygon [2009/06/27 11:19] – rocketboy
+++ code:uk_polygon [2010/10/15 06:58] (current) – Add C code to test if point is inside polygon fsphil
@@ Line 1: / Line 1: @@
 Code and KML for partial UK polygon.
+{{code:smalluk.jpg|}}
@@ Line 25: / Line 27: @@
 };
-</code KML>
+</code>
+<code KML>
 <kml xmlns="http://earth.google.com/kml/2.0">
 <Placemark>
-  <name>Small Map</name>
+  <name>Small UK</name>
   <Style>
     <LineStyle>
@@ Line 62: / Line 65: @@
 </code>
+====== C ======
+A C function to test if a point (x, y) is inside a polygon (poly, points). Returns 0 if outside, !0 if inside the polygon. poly points to an array of x, y coordinates of the polygon. points is the number of points in the array.
+<code c>
+int pointinpoly(float *poly, int points, float x, float y)
+{
+        float *p = poly;
+        float *l = &poly[points * 2 - 2];
+        int c = 0;
+        for(; points; points--, l = p, p += 2)
+        {
+                if(y < p[1] && y < l[1]) continue;
+                if(y >= p[1] && y >= l[1]) continue;
+                if(x < p[0] + (l[0] - p[0]) * (y - p[1]) / (l[1] - p[1])) continue;
+                c = !c;
+        }
+        return(c);
+}
+</code>