QgsCircle QgsCircle::from3Points( const QgsPoint &pt1, const QgsPoint &pt2, const QgsPoint &pt3, double epsilon )
{
QgsPoint p1, p2, p3;
if ( !isPerpendicular( pt1, pt2, pt3, epsilon ) )
{
p1 = pt1;
p2 = pt2;
p3 = pt3;
}
else if ( !isPerpendicular( pt1, pt3, pt2, epsilon ) )
{
p1 = pt1;
p2 = pt3;
p3 = pt2;
}
else if ( !isPerpendicular( pt2, pt1, pt3, epsilon ) )
{
p1 = pt2;
p2 = pt1;
p3 = pt3;
}
else if ( !isPerpendicular( pt2, pt3, pt1, epsilon ) )
{
p1 = pt2;
p2 = pt3;
p3 = pt1;
}
else if ( !isPerpendicular( pt3, pt2, pt1, epsilon ) )
{
p1 = pt3;
p2 = pt2;
p3 = pt1;
}
else if ( !isPerpendicular( pt3, pt1, pt2, epsilon ) )
{
p1 = pt3;
p2 = pt1;
p3 = pt2;
}
else
{
return QgsCircle();
}
QgsPoint center = QgsPoint();
double radius = -0.0;
// Paul Bourke's algorithm
double yDelta_a = p2.y() - p1.y();
double xDelta_a = p2.x() - p1.x();
double yDelta_b = p3.y() - p2.y();
double xDelta_b = p3.x() - p2.x();
if ( qgsDoubleNear( xDelta_a, 0.0, epsilon ) || qgsDoubleNear( xDelta_b, 0.0, epsilon ) )
{
return QgsCircle();
}
double aSlope = yDelta_a / xDelta_a;
double bSlope = yDelta_b / xDelta_b;
if ( ( qAbs( xDelta_a ) <= epsilon ) && ( qAbs( yDelta_b ) <= epsilon ) )
{
center.setX( 0.5 * ( p2.x() + p3.x() ) );
center.setY( 0.5 * ( p1.y() + p2.y() ) );
radius = center.distance( pt1 );
return QgsCircle( center, radius );
}
if ( qAbs( aSlope - bSlope ) <= epsilon )
{
return QgsCircle();
}
center.setX(
( aSlope * bSlope * ( p1.y() - p3.y() ) +
bSlope * ( p1.x() + p2.x() ) -
aSlope * ( p2.x() + p3.x() ) ) /
( 2.0 * ( bSlope - aSlope ) )
);
center.setY(
-1.0 * ( center.x() - ( p1.x() + p2.x() ) / 2.0 ) /
aSlope + ( p1.y() + p2.y() ) / 2.0
);
radius = center.distance( p1 );
return QgsCircle( center, radius );
}
double angleBetweenLines(const Line &line) const {
if (isPerpendicular(line)) return PI / 2;
return atan((parameters.A * line.parameters.B - line.parameters.A * parameters.B) /
(parameters.A * line.parameters.A + parameters.B * line.parameters.B));
}
