/// <summary>
/// overrides <see cref="Surface.Normal(double, double)"/>.
/// </summary>
/// <param name="u">Specifies the parameter u in [0,1]</param>
/// <param name="v">Specifies the parameter v in [0,1]</param>
/// <returns>the normal vector.</returns>
public override xyz Normal(double u, double v)
{
if (Distance < 0)
{
return(BasisSurface.vDerivation(u, v) & BasisSurface.uDerivation(u, v));
}
return(BasisSurface.uDerivation(u, v) & BasisSurface.vDerivation(u, v));
}
/// <summary>
/// overrides <see cref="Surface.vDerivation(double, double)"/>
/// </summary>
/// <param name="u">Specifies the parameter u in [0,1]</param>
/// <param name="v">Specifies the parameter v in [0,1]</param>
/// <returns>partial v derivation</returns>
public override xyz vDerivation(double u, double v)
{
return(BasisSurface.vDerivation(u, v));
}