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 // Created on: 1991-10-10
 // Created by: Jean Claude VAUTHIER
 // Copyright (c) 1991-1999 Matra Datavision
 // Copyright (c) 1999-2014 OPEN CASCADE SAS
 //
 // This file is part of Open CASCADE Technology software library.
 //
 // This library is free software; you can redistribute it and/or modify it under
 // the terms of the GNU Lesser General Public License version 2.1 as published
 // by the Free Software Foundation, with special exception defined in the file
 // OCCT_LGPL_EXCEPTION.txt. Consult the file LICENSE_LGPL_21.txt included in OCCT
 // distribution for complete text of the license and disclaimer of any warranty.
 //
 // Alternatively, this file may be used under the terms of Open CASCADE
 // commercial license or contractual agreement.
 
 #ifndef _Convert_ParameterisationType_HeaderFile
 #define _Convert_ParameterisationType_HeaderFile
 
 //! Identifies a type of parameterization of a circle or ellipse represented as a BSpline curve.
 //! For a circle with a center C and a radius R (for example a Geom2d_Circle or a Geom_Circle),
 //! the natural parameterization is angular. It uses the angle Theta made by the vector CM with
 //! the 'X Axis' of the circle's local coordinate system as parameter for the current point M. The
 //! coordinates of the point M are as follows:
 //! X   =   R *cos ( Theta )
 //! y   =   R * sin ( Theta )
 //! Similarly, for an ellipse with a center C, a major radius R and a minor radius r, the circle
 //! Circ with center C and radius R (and located in the same plane as the ellipse) lends its natural
 //! angular parameterization to the ellipse. This is achieved by an affine transformation in the
 //! plane of the ellipse, in the ratio r / R, about the 'X Axis' of its local coordinate system. The
 //! coordinates of the current point M are as follows:
 //! X   =   R * cos ( Theta )
 //! y   =   r * sin ( Theta )
 //! The process of converting a circle or an ellipse into a rational or non-rational BSpline curve
 //! transforms the Theta angular parameter into a parameter t. This ensures the rational or
 //! polynomial parameterization of the resulting BSpline curve. Several types of parametric
 //! transformations are available.
 //! TgtThetaOver2
 //! The most usual method is Convert_TgtThetaOver2 where the parameter t on the BSpline
 //! curve is obtained by means of transformation of the following type:
 //! t = tan ( Theta / 2 )
 //! The result of this definition is:
 //! cos ( Theta ) = ( 1. - t**2 ) / ( 1. + t**2 )
 //! sin ( Theta ) =      2. * t / ( 1. + t**2 )
 //! which ensures the rational parameterization of the circle or the ellipse. However, this is not
 //! the most suitable parameterization method where the arc of the circle or ellipse has a large
 //! opening angle. In such cases, the curve will be represented by a BSpline with intermediate
 //! knots. Each span, i.e. each portion of curve between two different knot values, will use
 //! parameterization of this type. The number of spans is calculated using the following rule: ( 1.2
 //! * Delta / Pi ) + 1 where Delta is equal to the opening angle (in radians) of the arc of the
 //! circle (Delta is equal to 2.* Pi in the case of a complete circle). The resulting BSpline curve
 //! is "exact", i.e. computing any point of parameter t on the BSpline curve gives an exact point on
 //! the circle or the ellipse. TgtThetaOver2_N Where N is equal to 1, 2, 3 or 4, this ensures the
 //! same type of parameterization as Convert_TgtThetaOver2 but sets the number of spans in the
 //! resulting BSpline curve to N rather than allowing the algorithm to make this calculation.
 //! However, the opening angle Delta (parametric angle, given in radians) of the arc of the circle
 //! (or of the ellipse) must comply with the following:
 //! -   Delta <= 0.9999 * Pi for the Convert_TgtThetaOver2_1 method, or
 //! -   Delta <= 1.9999 * Pi for the Convert_TgtThetaOver2_2 method.
 //! QuasiAngular
 //! The Convert_QuasiAngular method of parameterization uses a different type of rational
 //! parameterization. This method ensures that the parameter t along the resulting BSpline curve is
 //! very close to the natural parameterization angle Theta of the circle or ellipse (i.e. which uses
 //! the functions sin ( Theta ) and cos ( Theta ).
 //! The resulting BSpline curve is "exact", i.e. computing any point of parameter t on the BSpline
 //! curve gives an exact point on the circle or the ellipse.
 //! RationalC1
 //! The Convert_RationalC1 method of parameterization uses a further type of rational
 //! parameterization. This method ensures that the equation relating to the resulting BSpline curve
 //! has a "C1" continuous denominator, which is not the case with the above methods. RationalC1
 //! enhances the degree of continuity at the junction point of the different spans of the curve.
 //! The resulting BSpline curve is "exact", i.e. computing any point of parameter t on the BSpline
 //! curve gives an exact point on the circle or the ellipse.
 //! Polynomial
 //! The Convert_Polynomial method is used to produce polynomial (i.e. non-rational)
 //! parameterization of the resulting BSpline curve with 8 poles (i.e. a polynomial degree equal to
 //! 7). However, the result is an approximation of the circle or ellipse (i.e. computing the point
 //! of parameter t on the BSpline curve does not give an exact point on the circle or the ellipse).
 enum Convert_ParameterisationType
 {
   Convert_TgtThetaOver2,
   Convert_TgtThetaOver2_1,
   Convert_TgtThetaOver2_2,
   Convert_TgtThetaOver2_3,
   Convert_TgtThetaOver2_4,
   Convert_QuasiAngular,
   Convert_RationalC1,
   Convert_Polynomial
 };
 
 #endif // _Convert_ParameterisationType_HeaderFile

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