Method getSymmetryAxis

jni/venus/Extractor.cpp:182–271

}

cv::Vec4f Extractor::getSymmetryAxis(const std::vector<cv::Point2f>& points)
{
#if 0
	// right eye index 42, left eye index 48.
	// Make sure that right eye is one the right side. (no pun intended)
	assert(points[48].x - points[42].x > 1/* pixel */);

	cv::Point2f middle = (points[48] + points[42].x)/2;
	cv::Vec4f line;  // (vx, vy, x0, y0)  where (vx, vy) is a normalized vector collinear to the line and (x0, y0) is a point on the line.
	line[2] = middle.x;
	line[3] = middle.y;

	float k = (points[48].y - points[42].y) / (points[48].x - points[42].x);

	// atan(x) return angle in [-pi/2, pi/2], while atan2(y, x) return angle in [-pi, pi].
	// But we know that our x > 0, we can use atan directly.
	float theta = std::atan(k);
	line[0] = std::cos(theta);
	line[1] = std::sin(theta);
#else
	
	// those points are one the vertical line.
	std::vector<cv::Point2f> points_on_line;
	points_on_line.push_back(points[16]);
	points_on_line.push_back(points[ 6]);

	// right 15 14 13 12 11 10  9  8  7
	// left  17 18 19  0  1  2  3  4  5
	// (right + left)/2 are approximately on the line
	for(int i = 15, j = 17; i >= 7; --i, j = (j+1)%20)
		points_on_line.push_back((points[i] + points[j])/2);
	
	// eye brow
	for(int i = 20; i <= 24; ++i)
		points_on_line.push_back((points[i] + points[i + 7])/2);

	// eye, currently STASM doesn't detect left eyes precisely.
	// besides, iris is not fixed in center, not suitable for computing.
/*
	for(int i = 34; i <= 41; ++i)
		points_on_line.push_back((points[i] + points[i + 10])/2);
	points_on_line.push_back((points[42] + points[43])/2);
*/
	// nose
	points_on_line.push_back(points[53]);
	points_on_line.push_back((points[52] + points[54])/2);
	points_on_line.push_back(points[56]);
	points_on_line.push_back((points[62] + points[58])/2);
	points_on_line.push_back((points[55] + points[57])/2);
	points_on_line.push_back((points[61] + points[59])/2);
	points_on_line.push_back(points[60]);

	// mouth
	// mouth can varies a lot with respect to different expressions, so overlook lower lip.
	points_on_line.push_back(points[66]);
	points_on_line.push_back(points[71]);
	points_on_line.push_back((points[65] + points[67])/2);
	points_on_line.push_back((points[64] + points[68])/2);