public static double AngleVector0(
double x1, double y1,
double x2, double y2,
double x3, double y3)
{
return(Atan2(CrossProduct3Vector2DTests.CrossProductVector2D(x1, y1, x2, y2, x3, y3), DotProduct3Vector2DTests.DotProductVector2D(x1, y1, x2, y2, x3, y3)));
}
/// <summary>
/// For each set of three adjacent points A, B, C,
/// find the dot product AB · BC. If the sign of
/// all the dot products is the same, the angles
/// are all positive or negative (depending on the
/// order in which we visit them) so the polygon
/// is convex.
/// </summary>
/// <returns>
/// Return true if the polygon is convex.
/// </returns>
/// <acknowledgment>
/// http://csharphelper.com/blog/2014/07/determine-whether-a-polygon-is-convex-in-c/
/// </acknowledgment>
public static bool IsConvex(PolygonContour2D polygon)
{
var got_negative = false;
var got_positive = false;
var num_points = polygon.Points.Count;
int B, C;
for (var A = 0; A < num_points; A++)
{
B = (A + 1) % num_points;
C = (B + 1) % num_points;
var cross_product = CrossProduct3Vector2DTests.CrossProductVector2D(
polygon.Points[A].X, polygon.Points[A].Y,
polygon.Points[B].X, polygon.Points[B].Y,
polygon.Points[C].X, polygon.Points[C].Y);
if (cross_product < 0)
{
got_negative = true;
}
else
{
got_positive |= cross_product > 0;
}
if (got_negative && got_positive)
{
return(false);
}
}
// If we got this far, the polygon is convex.
return(true);
}
public static double AngleVector1(
double aX, double aY,
double bX, double bY,
double cX, double cY)
{
// Get the dot product.
var dotProduct = DotProduct3Vector2DTests.DotProductVector2D(aX, aY, bX, bY, cX, cY);
// Get the cross product.
var crossProduct = CrossProduct3Vector2DTests.CrossProductVector2D(aX, aY, bX, bY, cX, cY);
// Calculate the angle.
return(Atan2(crossProduct, dotProduct));
}
