Distance between point and finite line in objective-c - objective-c

Question

I've looked up some formulas relating to finding the distance a point and a line. On this page, I used example 14
http://mathworld.wolfram.com/Point-LineDistance2-Dimensional.html
I have a method that has turned into this:
+(bool) checkPointNearBetweenPointsWithPointA:(CGPoint)pointA withPointB:(CGPoint)pointB withPointC:(CGPoint)pointC withLimit:(float)limit {
float A = pointB.x - pointA.x;
float B = pointA.y - pointC.y;
float C = pointA.x - pointC.x;
float D = pointB.y - pointA.y;
float dividend = fabs( A * B ) - ( C * D );
float divisor = sqrt(pow(A,2) + pow(D,2));
float distanceBetweenPointAndLine = dividend / divisor;
if(distanceBetweenPointAndLine < limit){
NSLog(#"distanceBetweenPointAndLine = %f",distanceBetweenPointAndLine);
return YES;
}
return NO;
}
The problem is that it still returns YES if I'm passed point B, if the line segment is drawn like B----A. Other screwed up things happen to depending on which angle the line is drawn. Just wondering if I need to consider anything else if testing to see if a point is near a finite line. Most examples I see online deal with lines of infinite length.

Answer 1

try my code below. line is considered to exist between points A & B (regardless of how you draw it B->A or A->B ) and point C is the point in consideration to measure the distance.
+ (bool) checkPointNearBetweenPointsWithPointA:(CGPoint)pointA
withPointB:(CGPoint)pointB
withPointC:(CGPoint)pointC
withLimit:(float)limit
{
CGFloat slopeLine = atan((pointB.y-pointA.y)/(pointB.x-pointA.x) );
CGFloat slopePointToPointA = -1 *atan((pointC.y-pointA.y)/(pointC.x-pointA.x));
CGFloat innerAngle = slopeLine + slopePointToPointA;
CGFloat distanceAC = sqrtf(pow(pointC.y-pointA.y,2) + pow(pointC.x-pointA.x,2));
CGFloat distanceBetweenPointAndLine = fabs(distanceAC * sin(innerAngle));
NSLog(#"distanceBetweenPointAndLine = %f",distanceBetweenPointAndLine);
NSLog(#"is exceeding limit ? %#",distanceBetweenPointAndLine > limit ? #"YES":#"NO");
if(distanceBetweenPointAndLine < limit)
{
return YES;
}
return NO;
}