Polygon overlap detection, javascript

PolygonOverlap.js

function determinant(vector1, vector2)
                    {
                        
                        return vector1.x * vector2.y - vector1.y * vector2.x;
                    }
                
                function lineSegmentsIntersect(_segment1_Start, _segment1_End, _segment2_Start, _segment2_End)
                    {  //note the use of 'subtract'
                        det = determinant(_segment1_End.subtract(_segment1_Start), _segment2_Start.subtract(_segment2_End));
                        t = determinant(_segment2_Start.subtract(_segment1_Start), _segment2_Start.subtract(_segment2_End)) / det;
                        u = determinant(_segment1_End.subtract(_segment1_Start), _segment2_Start.subtract(_segment1_Start)) / det;
                        return (t >= 0) && (u >= 0) && (t <= 1) && (u <= 1);
                    }
                
                
                    
                function PointCollectionContainsPoint(area, point)
                    {
                        start = new Point(-100, -100);
                        intersections = 0;
                    
                        for (i = 0; i < area.length; i++)
                        {
                            if (lineSegmentsIntersect(area[i], area[(i + 1) % area.length], start, point))
                            {
                                intersections++;
                            }
                        }
                    
                        return (intersections % 2) == 1;
                    }
                    
                function PointCollectionsOverlap_Fast(area1, area2)
                    {
                        for (i = 0; i < area1.length; i++)
                        {
                            for (j = 0; j < area2.length; j++)
                            {
                                if (lineSegmentsIntersect(area1[i], area1[(i + 1) % area1.length], area2[j], area2[(j + 1) % area2.length]))
                                {
                                    return true;
                                }
                            }
                        }
                    
                        if (PointCollectionContainsPoint(area1, area2[0]) ||
                            PointCollectionContainsPoint(area2, area1[0]))
                        {
                            return true;
                        }
                    
                        return false;
                    }
                    

                //Building array of points  -- probably won't be relevant to your needs. 
         //I'm breaking apart google api objects here
                
                count = 0;
                area1= new Array(); //to be a collection of points
                while(count< vertex.length){
                    innercount = 0;
                    
                    lat = vertex[count]['$a'];
                    lng = vertex[count]['ab'];
                    
                    pAdd = new Point(lng, lat);
                    
                    if(area1.length < 1){
                            area1 = [pAdd];
                        } else
                        {
                            area1.push(pAdd);
                            }
                    
                    count++;
                }
                
                count = 0;
                area2=[]; //collection of points


                area2= new Array();
                count = 0;
                while(count < compareArray.length){
                    
                //for each compared polygon
                    innercount = 0;
                    while(innercount< compareArray[count].length){
                    //console.log('compareArray');
                    //console.debug(compareArray[count][innercount]);
                    lat = compareArray[count][innercount]['$a'];
                    lng = compareArray[count][innercount]['ab'];
                    
                    pAdd = new Point(lng, lat);
                    
                    if(area1.length < 1){
                            area2 = [pAdd];
                        } else {
                            area2.push(pAdd);
                            }
                    
                    innercount++;
                    }
                

                
                PointCollectionsOverlap_Fast(area1, area2);