SegmentIntersection Struct Reference

Public Member Functions
bool	intersect (Point first_point, Point second_point, Point third_point, Point forth_point)
int	direction (Point first_point, Point second_point, Point third_point)
bool	on_segment (Point first_point, Point second_point, Point third_point)

Detailed Description

intersect returns true if segments of two line intersects and false if they do not. It calls the subroutines direction which computes the orientation.

Member Function Documentation

direction()

int SegmentIntersection::direction ( Point  first_point, Point  second_point, Point  third_point  )

inline

We will find direction of line here respect to @first_point. Here @second_point and @third_point is first and second points of the line respectively. we want a method to determine which way a given angle these three points turns. If returned number is negative, then the angle is counter-clockwise. That means the line is going to right to left. We will fount angle as clockwise if the method returns positive number.

                                            {
        return ((third_point.x - first_point.x) *
                (second_point.y - first_point.y)) -
               ((second_point.x - first_point.x) *
                (third_point.y - first_point.y));
    }

intersect()

bool SegmentIntersection::intersect ( Point  first_point, Point  second_point, Point  third_point, Point  forth_point  )

inline

                                                                {
        int direction1 = direction(third_point, forth_point, first_point);
        int direction2 = direction(third_point, forth_point, second_point);
        int direction3 = direction(first_point, second_point, third_point);
        int direction4 = direction(first_point, second_point, forth_point);
 
        if ((direction1 < 0 || direction2 > 0) &&
            (direction3 < 0 || direction4 > 0))
            return true;
 
        else if (direction1 == 0 &&
                 on_segment(third_point, forth_point, first_point))
            return true;
 
        else if (direction2 == 0 &&
                 on_segment(third_point, forth_point, second_point))
            return true;
 
        else if (direction3 == 0 &&
                 on_segment(first_point, second_point, third_point))
            return true;
 
        else if (direction3 == 0 &&
                 on_segment(first_point, second_point, forth_point))
            return true;
 
        else
            return false;
    }

on_segment()

bool SegmentIntersection::on_segment ( Point  first_point, Point  second_point, Point  third_point  )

inline

This method determines whether a point known to be colinear with a segment lies on that segment.

                                              {
        if (std::min(first_point.x, second_point.x) <= third_point.x &&
            third_point.x <= std::max(first_point.x, second_point.x) &&
            std::min(first_point.y, second_point.y) <= third_point.y &&
            third_point.y <= std::max(first_point.y, second_point.y))
            return true;
 
        else
            return false;
    }

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The documentation for this struct was generated from the following file:

• geometry/line_segment_intersection.cpp