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--- code:uk_polygon [2009/06/27 11:05] – created rocketboy
+++ code:uk_polygon [2010/10/15 06:58] (current) – Add C code to test if point is inside polygon fsphil
@@ Line 2: / Line 2: @@
 Code and KML for partial UK polygon.
+{{code:smalluk.jpg|}}
+<code UKpolygon>
 coordinate cutdownpoly[17] =
 { // Latitude,Longtitude
@@ Line 23: / Line 27: @@
 };
+</code>
+<code KML>
+<kml xmlns="http://earth.google.com/kml/2.0">
+<Placemark>
+  <name>Small UK</name>
+  <Style>
+    <LineStyle>
+      <color>ff0000ff</color>
+    </LineStyle>
+  </Style>
+  <LineString>
+<altitudeMode>absolute</altitudeMode>
+    <coordinates>
+ -2.166,53.166
+ -0.1,53.166
+ -0.1,52.833
+.333,52.7
+.7,52.87
+.25,52.833
+.5,52.666
+.5,52.416
+.166,52.083
+.3,51.666
+ -0.666,51.666
+ -0.666,51.166
+ -2.166,51.166
+ -2.166,52.333
+ -1.666,52.333
+ -1.666,52.666
+ -2.166,52.666
+    </coordinates>
+  </LineString>
+</Placemark>
+</kml>
+</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>