objective c - Distance between two points on circle in specific direction -

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i have 2 points on circle, (x1y1) , (x2y2). how calculate distance between them in counter , clock wise direction. currently, using following formula calculate distance between 2 points on circle. please suggest.

- (cgfloat)calculatedistancebetween:(cgpoint)point1 point2:(cgpoint)point2 {     cgfloat dx = point2.x - point1.x;     cgfloat dy = point2.y - point1.y;     return sqrt(dx*dx + dy*dy ); }

this maths question really. you're looking arc length (which equals angle in radians multiplied radius)

your function stands can't calculate arc length, because doesn't know circle (it takes 3 points define circle).

- (cgfloat)calculateshortestarcdistancebetween:(cgpoint)point1 point2:(cgpoint)point2 center:(cgpoint)center {     cgfloat dx1 = point1.x - center.x;     cgfloat dy1 = point1.y - center.y;     cgfloat dx2 = point2.x - center.x;     cgfloat dy2 = point2.y - center.y;     cgfloat angle1 = atan2f( dy1, dx1 );     cgfloat angle2 = atan2f( dy2, dx2 );     cgfloat angle = angle1 - angle2;     if(      angle >  m_pi ) angle -= m_pi * 2;     else if( angle < -m_pi ) angle += m_pi * 2;     return fabs( angle ) * sqrtf( dx1 * dx1 + dy1 * dy1 ); }  - (cgfloat)calculatedirectedarcdistancebetween:(cgpoint)point1 point2:(cgpoint)point2 center:(cgpoint)center {     cgfloat dx1 = point1.x - center.x;     cgfloat dy1 = point1.y - center.y;     cgfloat dx2 = point2.x - center.x;     cgfloat dy2 = point2.y - center.y;     cgfloat angle1 = atan2f( dy1, dx1 );     cgfloat angle2 = atan2f( dy2, dx2 );     cgfloat angle = angle1 - angle2;     if( angle < 0 ) angle += m_pi * 2;     return angle * sqrtf( dx1 * dx1 + dy1 * dy1 ); }

most of tricky bit making sure ranges correct (atan2 gives values -pi +pi, after getting difference between 2 angles must re-normalise them)


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