How to find points with specific degree on the contour (Opencv) - opencv

Question

I have the points of the contour and i want to get the (x,y) of the points that are on specific degree. From the attached image, i want to get the yellow points.

Answer 1

I used the hint that #Aleksander and #Zaw gave me.
The centroid of the contour was used as one point to draw the lines and i used the line equations to get the second point of each line and draw it.
y - y1 = m (x - x1)
to get m we used the following equations
arctan( **y** of the centroid / **x** of the centroid) - angle in radiant = Phi
tan(Phi) = m
then i used
y = m (x - x1) + y1
when x1 and y1 is the centroid point, and x is the assumed coordinate of the second point needed to draw the line.
void MyDraw (Mat Draw, vector<Point> hull,Scalar color,int thickness){
std::vector<std::vector<cv::Point> > T = std::vector<std::vector<cv::Point> >(1,hull);
drawContours(Draw, T, -1, color, thickness);}
Point GetCentroidOfConvexHull(vector<Point> Hull){
// Get the moments
Moments mu;
mu= moments(Hull, false );
// Get the mass centers:
return Point( mu.m10/mu.m00 , mu.m01/mu.m00 );}
void _tmain(int argc, _TCHAR* argv[]){
vector<vector<Point>> contours;
vector<Point> hull;
Mat testContour = Mat::zeros(width, height,CV_8UC3);
Mat testLine = Mat::zeros(width, height,CV_8UC3);
Mat andResult;
Point centroid;
findContours(Dilated,contour,hierarchy,CV_RETR_EXTERNAL,CV_CHAIN_APPROX_NONE,Point (0,0));
convexHull(contour,hull,false);
centroid = GetCentroidOfConvexHull(hull);
MyDraw(testContour,hull,White,1);
Rect myRect = boundingRect(hull);
imshow("test contour",testContour);
waitKey(0);
float degrees[8] = {0,45,90,135,180,225,270,315};
Point point;
// for each degree
for (int d = 0 ; d < 8 ; d++){
//Get line equation from the slope and the center point of the contour
float m = std::tan( std::atan2((double)centroid.y,(double)centroid.x) - (degrees[d]*3.14/180));
// using the upper left and lower right points to get the x of the other point
if ((d >= 0 && d <= 2) || d == 7) point.x = myRect.tl().x;
else point.x = myRect.br().x;
point.y = (int)(m * (float)(point.x - centroid.x) + centroid.y);
line(testLine,centroid,point,White,1,8);}
imshow("test Line",testLine);
waitKey(0);
// and operation
andResult = testContour & testLine;
imshow("Anding Result",andResult);
waitKey(0);}
After drawing the contour and the lines, i did a bit wise AND operation to get the intersection between the lines and the contour.