# Distance Between Point and Line Segment

Actionscript:
1. /**
2. Original function by Pieter Iserbyt:
3. http://local.wasp.uwa.edu.au/~pbourke/geometry/pointline/DistancePoint.java
4. from Paul Bourke's website:
5. http://local.wasp.uwa.edu.au/~pbourke/geometry/pointline/
6. */
7. function pointToLineDistance(p1:Sprite, p2:Sprite, p3:Sprite):Number {
8.     var xDelta:Number = p2.x - p1.x;
9.     var yDelta:Number = p2.y - p1.y;
10.     if ((xDelta == 0) && (yDelta == 0)) {
11.         // p1 and p2 cannot be the same point
12.         p2.x += 1;
13.         p2.y += 1;
14.         xDelta = 1;
15.             yDelta = 1;
16.     }
17.     var u:Number = ((p3.x - p1.x) * xDelta + (p3.y - p1.y) * yDelta) / (xDelta * xDelta + yDelta * yDelta);
18.     var closestPoint:Point;
19.     if (u <0) {
20.         closestPoint = new Point(p1.x, p1.y);
21.     } else if (u> 1) {
22.         closestPoint = new Point(p2.x, p2.y);
23.     } else {
24.         closestPoint = new Point(p1.x + u * xDelta, p1.y + u * yDelta);
25.     }
26.     return Point.distance(closestPoint, new Point(p3.x, p3.y));
27. }
28.
29. /**
30. Test out the function
31. */
32.
33. var dotA:Sprite = dot(100, 100);
34. var dotB:Sprite = dot(200, 200);
35. var dotC:Sprite = dot(150, 100, 0x0000FF);
36. var txt:TextField = TextField(dotC.addChild(new TextField()));
37. with(txt) x = 5, y = 5, autoSize = "left", selectable = false, mouseEnabled = false;
38.
40. function onLoop(evt:Event):void {
41.     graphics.clear();
42.     graphics.lineStyle(0,0x000000);
43.     graphics.moveTo(dotA.x, dotA.y);
44.     graphics.lineTo(dotB.x, dotB.y);
45.     txt.text = pointToLineDistance(dotA, dotB, dotC).toFixed(2);
46. }
47.
48. // draggable dot
49. function dot(xp:Number, yp:Number, col:uint = 0xFF0000, rad:Number=4):Sprite {
50.     var s:Sprite = Sprite(addChild(new Sprite));
51.     s.x = xp;
52.     s.y = yp;
54.     s.buttonMode = true;
56.     return s;
57. }
58. function onDrag(evt:MouseEvent):void { evt.currentTarget.startDrag() }
60. function onUp(evt:MouseEvent):void{stopDrag() }

Last night I was working late and found myself in need of a way to calculate the distance between a point and a line. After a quick google search I found myself once again on Paul Bourke's extremely useful website. I was in a rush, so I just quickly ported the java code (by Pieter Iserbyt) and wrote this test snippet to make sure it works.

This code could be optimized a bit, but it works nicely.

I needed this for a commercial project, but as I was porting the code I thought of an interesting way to use this code to draw a gradient - may write and post that tomorrow.

1. elisa whitlock
Posted August 5, 2009 at 6:25 pm | Permalink

this is not helpful at all

2. Zevan
Posted August 5, 2009 at 6:29 pm | Permalink

hey elisa, I assume your not an actionscript programmer - and were just looking for the math… and if thats the case this link should be helful:

http://local.wasp.uwa.edu.au/~pbourke/geometry/pointline/

3. dfrdf
Posted April 21, 2011 at 4:26 pm | Permalink

Thanks for the code, it was really helpful, along with your line intersection code.

4. Pablo
Posted May 6, 2011 at 1:04 pm | Permalink

This was truly useful to me! It worked great!
Thanks! ^^

5. Ivan
Posted December 27, 2011 at 5:41 am | Permalink

Thanks, its great.

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