Point In Polygon

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Andy_A	Created : 23 May 2008 Edited : 23 May 2008 Language : Blitz Point In Polygon Check if point is inside of polygon
Here's a fast way to check if a point is inside of a polygon. On my ancient machine I can check about one thousand points per millisecond (your mileage will vary...) AppTitle "Point in Polygon" Global sw% = 640 Global sh% = 480 Graphics sw%, sh%, 32, 1 SeedRnd MilliSecs() Dim xp#(99), yp#(99) ClsColor 0,40,64 Repeat Cls pip% = 0 minX# = sw% maxX# = 0 minY# = sh% maxY# = 0 drawGrid() st% = MilliSecs() numPoints% = Rand(3,10) For i% = 0 To numPoints%-1 xp(i%) = Rnd(100,540) yp(i%) = Rnd(60,420) minX = min(minX, xp(i%)) maxX = max(maxX, xp(i%)) minY = min(minY, yp(i%)) maxY = max(maxY, yp(i%)) Next Color 0,255,255 Text 5,0,"Number of points = "+numPoints Color 255,0,32 For x# = minX To maxX r# = 255.0 Color r,0,32 For y# = minY To maxY If y And 1 Then r = r - 1.4 Color r,0,32 End If If pointInPoly(x,y,numPoints%) Then Plot x,y: pip% = pip% + 1 Next Next Color 255,255,255 For i% = 0 To numPoints%-2 Line xp(i%), yp(i%), xp(i%+1), yp(i%+1) Next Line xp(numPoints%-1), yp(numPoints%-1), xp(0), yp(0) Color 0,255,255 et = MilliSecs()-st Text 5,15,"ET: "+et+" ms Number of points in Poly: "+pip% Text 150,460,"Press a key to continue. Press [ESC] to exit." ;================================================================== ;== Comment to remove bounding rectangle (minX,minY - maxX,maxY) == ;================================================================== Rect minX, minY, maxX-minX+1, maxY-minY+1, False ;================================================================== Flip WaitKey Until KeyHit(1) End Function pointInPoly(x#, y#, points%) Local i%, j%, c% Local v1#, v2#, v3#, v4#, v5#, v6#, v7# c = 0 For i = 0 To points-1 j = (i+1) Mod points v1 = (yp(i) <= y) v2 = (y < yp(j)) v3 = (yp(j) <= y) v4 = (y < yp(i)) v5 = ( xp(j)-xp(i) ) * ( y-yp(i) ) v6 = (yp(j)-yp(i)) If v6 = 0.0 Then v6 = 0.0001 v7 = xp(i) If ( ( (v1 And v2) Or ( v3 And v4) ) And ( x < v5 / v6 + v7) ) Then c = 1 - c Next Return c End Function Function min#(flt1#, flt2#) If flt1 < flt2 Then Return flt1 Else Return flt2 End Function Function max#(flt1#, flt2#) If flt2 > flt1 Then Return flt2 Else Return flt1 End Function Function drawGrid() Color 128,128,192 For x = 20 To sw-20 Step 20 Line x,40,x, sh-40 Next For y = 40 To sh-40 Step 20 Line 20,y,sw-20,y Next End Function --v

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Point In Polygon

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