angle

I have coded as below for half circle in iOS using UIBezierPath and CAShapeLayer . clockWiseLayer = [[CAShapeLayer alloc] init]; CGFloat startAngle = -M_PI_2; CGFloat endAngle = M_PI + M_PI_2; CGFloat width = CGRectGetWidth(imageView.frame)/2.0f + 30; CGFloat height = CGRectGetHeight(imageView.frame)/2.0f +50; CGPoint centerPoint = CGPointMake(width, height); float radius = CGRectGetWidth(imageView.frame)/2+10; clockWiseLayer.path = [UIBezierPath bezierPathWithArcCenter:centerPoint radius:radius startAngle:startAngle endAngle:endAngle clockwise:YES].CGPath; clockWiseLayer.fillColor = [UIColor

I want to reverse a sin / cos operation to get back an angle, but I can't figure out what I should be doing. I have used sin and cos on an angle in radians to get the x/y vector as such: double angle = 90.0 * M_PI / 180.0; // 90 deg. to rad. double s_x = cos( angle ); double s_y = sin( angle ); Given s_x and s_y , is it possible to get back the angle? I thought atan2 was the function to use, but I'm not getting the expected results. atan2(s_y, s_x) should give you the correct angle. Maybe you have reversed the order of s_x and s_y . Also, you can use the acos and asin functions directly on s_x

I am working on a spatial analysis problem and part of this workflow is to calculate the angle between connected line segments. Each line segment is composed of only two points, and each point has a pair of XY coordinates (Cartesian). Here is the image from GeoGebra. I am always interested in getting a positive angle in 0 to 180 range . However, I get all kind of angles depending on the order of vertices in input line segments. The input data I work with is provided as tuples of coordinates. Depending on the vertex creation order, the last/end point for each line segment can be different. Here

In svg we have method element.getCTM() which returns a SVGMatrix as: [a c e][b d f][0 0 1] I want to calculate sx , sy and angle of rotation from this matrix. There is a lot to read and learn on this subject. I'll give a basic answer, but be aware, if you are trying to do a game or animations this is NOT the way to do it. a == sx and d == sy , so you'll access these like this: var r, ctm, sx, sy, rotation; r = document.querySelector('rect'); // access the first rect element ctm = r.getCTM(); sx = ctm.a; sy = ctm.d; Now for the rotation a == cos(angle) and b == sin(angle) . Asin and acos can't