Intersection Points of Two Circles

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Andy_A	Created : 01 April 2011 System : Windows Language : Blitz Intersection Points of Two Circles Get the intersection coords
I posted this in response to a question on BRL forum. ; Source: https://paulbourke.net/geometry/2circle/ ; C source code example by Tim Voght ; Ported to BlitzPlus 2011.04.01 ; by Andy_A AppTitle "Circle to Circle intersection points" Graphics 800,600,32,2 SetBuffer BackBuffer() SeedRnd MilliSecs() Global xi1#, yi1#, xi2#, yi2# ;the intersection coords While Not(KeyHit(1)) Cls rad1# = Rand(10,20)10.0 rad2# = Rand(10,20)10.0 cx1# = Rand(rad1, 800-rad1) cy1# = Rand(rad1, 600-rad1) cx2# = Rand(rad2, 800-rad2) cy2# = Rand(rad2, 600-rad2) ;show the circle center points Color 255,0,0 Oval cx1-3,cy1-3,6,6,True Oval cx2-3,cy2-3,6,6,True ;show the circles Color 255, 255, 0 Oval cx1-rad1, cy1-rad1, rad12, rad12,False Oval cx2-rad2, cy2-rad2, rad22, rad22,False ;check for intersection of circles chk% = c2c(cx1,cy1,rad1,cx2,cy2,rad2) Select chk Case -1 Color 255,0,0 Text 5,20,"One circle contains the other, no intersection" Case 0 Color 255,255,0 Text 5,20,"Circles do not intersect' Case 1 ;show the coordinates and draw a line connecting intersection points Color 0,255,0 Text 5,20,"The circles intersect at:" Text 5,40,xi1+", "+yi1 Text 5,60,xi2+", "+yi2 Oval xi1-3, yi1-3, 6, 6, True Oval xi2-3, yi2-3, 6, 6, True Color 255, 0, 255 Line(xi1, yi1, xi2, yi2) End Select Color 255,255,255 Text 400,580,"Press a key for more examples, [ESC] to exit",True Flip WaitKey() Wend End Function c2c(x0#, y0#, r0#, x1#, y1#, r1#) Local a#, dx#, dy#, d#, h#, rx#, ry#, x2#, y2# ; This function checks for the intersection of two circles. ; If one circle is wholly contained within the other a -1 is returned ; If there is no intersection of the two circles a 0 is returned ; If the circles intersect a 1 is returned and ; the coordinates are placed in xi1, yi1, xi2, yi2 ; dx and dy are the vertical And horizontal distances between ; the circle centers. dx = x1 - x0 dy = y1 - y0 ; Determine the straight-Line distance between the centers. d = Sqr((dydy) + (dxdx)) ; Check for solvability. If (d > (r0 + r1)) Then ;no solution. circles do Not intersect Return 0; End If If (d < Abs(r0 - r1)) Then ; no solution. one circle is contained in the other Return -1 End If ; 'point 2' is the point where the Line through the circle ; intersection points crosses the Line between the circle ; centers. ; Determine the distance from point 0 To point 2. a = ((r0r0) - (r1r1) + (dd)) / (2.0 d) ; Determine the coordinates of point 2. x2 = x0 + (dx * a/d) y2 = y0 + (dy * a/d) ; Determine the distance from point 2 To either of the ; intersection points. h = Sqr((r0r0) - (aa)) ; Now determine the offsets of the intersection points from ; point 2. rx = -dy * (h/d) ry = dx * (h/d) ; Determine the absolute intersection points. xi1 = x2 + rx xi2 = x2 - rx yi1 = y2 + ry yi2 = y2 - ry Return 1 End Function --v

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Intersection Points of Two Circles

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