Point in Polgon

pointInPolygon.js

// https://github.com/zz85/
// implements Point - in - Polygon 
// described in "A Winding Number and Point-in-Polygon Algorithm"
// returns 0 if point is not in polygon
// returns n > 0 if contour winds around point in counter-clockwise manner n times
// returns n < 0 if contour winds around point in clockwise manner -n times
function pointInPolygon(point, contour) {
    // Creates a copy of contour
    var adjustedContour = [];
    var i,il;
    for (i=0, il=contour.length; i<il; i++ ) {
        adjustedContour[i] = contour.clone().subSelf(point);
    }
    
    var w = 0; // Init winding number to 0;
    
    var j;
    for (i=0, j=1;i<il;i++,j++) {
        
        if (j==il) {
            j = 0;
        }
        
        var v1 = adjustedContour[i];
        var v2 = adjustedContour[j];
        if (v1.y * v2.y < 0) {
            // line crosses x axis 
            var r = v1.x + v1.y * (v2.x - v1.x)/(v1.y - v2.y);
            
            // r is x-coordinate intersection of v1-v2 with x axis
            if (r>0) {
                // line cross positive x-axis
                if (v1.y<0) {
                    w++;
                } else {
                    w--;
                }
            }
        } else if ((v1.y==0) && (v1.x > 0)) {
            // v1 is on positive x axis
            if (v2.y > 0 ) {
                w += 0.5;
            } else {
                w -= 0.5;
            }
        } else if ((v2.y==0) && (v2.x>0)) {
            // v2 is on the positive x axis
            if (v1.y < 0) {
                w += 0.5;
            } else {
                w -= 0.5;
            }
        }
    }
    
    return w;

}